LT5 miss at all speeds

[Big D]

Hi all, my 90 ZR1 is missing/rough running at all speeds especially when it reaches operating temp. Turning the poser key on and off made no difference. I get spark at all plugs but when I pulled the #3 wire the idle didn't change much. Let her cool down and pulled the plug and the plug showed little evidence of firing. Didn't smell much of fuel either. Pulled a couple of others and they looked good. Next step was to check injector resistance and it was as follows: 1:15.3, 2;14.5, 3:5.7, 4:14.7, 5:13.0. 6:17.8, 7:15.1 and 8:17.3. I replaced the #3 plug and still the same. this time I checked the injector resistance when it was still hot and got the following:1:18.2, 2;19.8, 3:8.0, 4:19.8, 5:11.0. 6:20.6, 7:18.8 and 8:20.4. Now I'm thinking maybe a bad injector at #3 and maybe #5. If so, looks like I'll be pulling the plenum for the first time, what fun. Any suggestions would be appreciated
Big D
'90 ZR1
'69 L46/M21

[TomZR1]

Change your coil packs,I had same problem.IDID all the tests,fuel pressure new plugs wires,even thought bad gas,

[Dynomite]

Hi all, my 90 ZR1 is missing/rough running at all speeds especially when it reaches operating temp. Big D
'90 ZR1
'69 L46/M21

Welcome to the Forum :handshak:

Injectors need replacing ;)

[tomcat]

I agree with all the above posts. Take your time, their are folks in Oregon & Washington that can help you.

Manfred E.......:fahne:
91 #906

[Paul Workman]

Jon at FIC can set you up with a new set of stainless injectors and gaskets and seals (Gaskets c/o Jerry's Gaskets, BTW). I use the Accel #150821s (from Summit Racing) with no complaints for 4 years running now.

Note: As for coil packs, I installed fresh coils with GM coil (direct replacement) "while I was in there" too. (When in doubt of what the readings should be, I measured resistance on both the primary and secondary windings, looking for consistency. However, one of the coils measured "open" between output terminals, so I replaced the all. All the readings then were the same across the lot, and the car runs great!) That was 6 years and 20k miles ago w/ no issues with them since.

[Big D]

thanks everyone for your inputs. Looks like I will be going under the plenum for the first time. Should be a good time....... Looking forward to getting her running back the way she should.

[Paul Workman]

Entering under the plenum is a "right of passage" for LT5 owners, it seems.

Might consider R&R'ing the started solenoid high-current contacts; set ya back around $10 or so.

Plug wires?

Vacuum lines, check valves, rubber unions = OK?

Secondary actuators and linkage works OK?

[Dynomite]

thanks everyone for your inputs. Looks like I will be going under the plenum for the first time. Should be a good time....... Looking forward to getting her running back the way she should.


Removing Plenum (including the 10 minute Plenum Removal) (http://forums.corvetteforum.com/c4-zr-1-discussion/3005470-tech-info-lt5-modifications-rebuild-tricks-500-hp-4.html#post1581663365)

Do as Paul suggests and clean the Valley Drain under the Starter when you are there. Other "stuff" in my signature :p

[Big D]

Looks like I'm going to go with the injectors from FIC. Can anyone suggest which brand of coils I should go with and where to get them.

thanks again everyone,
Big D

[efnfast]

OEM coils. Get them from Jerrys Gaskets.

[Jagdpanzer]

I like the MSD 8224 DIS coils.
Not that I notice any improved performance, I just like their red color
http://www.msdignition.com/Products/Coils/Stock_Replacement/8224_-_GM_Coil_Pack,_2_Tower_Style.aspx

[Billy Mild]

I bought mine from Advance Auto Parts. You can get MSD brand from them and usually have coupon deals to bring the cost down.

[efnfast]

Jerry supports the group. Buy them from Jerry.

[Mystic ZR-1]

A couple months ago, I got 4 new AC/Delco coils from Amazon $100 and a few cents delivered.

[Billy Mild]

A couple months ago, I got 4 new AC/Delco coils from Amazon $100 and a few cents delivered.

DANG. That is a good deal. I paid a little more for the BWD brand.

[Big D]

Ok everyone, Got the plenum off with no problem. Way easier then what I had imagined with all the good info on the Registry. Took about 40 minutes and broke nothing. However, I tried a suggested method for anti-freeze removal, just drain the plenum, and I would not advise that method. After releasing the plenum, antifreeze began bubbling up from the two holes in the injector housing. Plugged the holes quickly and then drained the radiator. Saving ten minutes at first cost me hours in cleanup. Dang, I hate antifreeze. The valley was extremely clean, prior to the antifreeze dump and all connectors and hoses are in very good shape. Well, at least I know the valley drain works just fine.Tested the wires and they come in at 7.5-9 K ohms for all, well within spec. Also checked the coils, all 4 coil resistance within spec. Also did a visual of the coils and they all look good, no signs of heat deterioration or cracking so I am going to let them go and just change out the injectors. I may end up regretting this decision but I was going to go with stock coils anyway so I don't see the advantage at this point. This is a very low mileage car. Looking forward to installing the new FIC injectors and getting her back on the road.

Big D
69 L46, M21
90 ZR1
95 Suzuki 1200 Bandit
2014 Triumph Thruxton

[Dynomite]

Never heard of draining the coolant from the plenum ;)

I would suggest blocking those two coolant passages in injector housings. That would then be an end to any messing with coolant when removing Plenum.

Oh. Just make sure when you get Plenum back on and coolant refilled that the two Injector Housing Coolant Manifolds are getting warm within a minute of firing up the engine :cheers:

[IMZZ]

I'll be doing the same thing this week. Let us know how everything turns out. Let me know what you think of the FIC injectors.

[Big D]

got the new FIC injectors in. So far so good. They look high quality and I think they will do the trick. Ordered them on Tues, got them Weds. Easy install. I released the old injectors from the fuel rails first and then removed them from the injector housings. Watch for fuel leaks. Have rags available. Seemed to be the easier way. Then installed the new injectors to the fuel rails and then installed them into the injector housings. All went together real easy. Taking your time is the best advice and follow all of the good info on this site. Helped tons. Took it out for a test beat and it screamed to 6500. Like a whole different car. I do have one problem, I have a slight miss when at idle or just idling down the road. Anything off idle up to floored and it doesn't miss at all. Wasn't able to get new plugs for it on Sunday so I had to re-install the old ones. Hoping maybe it is a bad plug. Didn't have time to troubleshoot any further either. All coils and wires checked out within specs. Won't be able to get back to it until next weekend.

[Big D]

hi everyone, couldn't figure out the miss so i put in new coil packs, wires and plugs. Still missing at low idle and while idling down the road. Also, get a bad hesitation off idle. Still screams to 7 grand though. So tonight, after putting the new plugs in, i have isolated the miss to number 6. Pulled the wires on all other plugs and the idle changes noticeably except for number 6. Pulled the #6 plug and it is bone dry, never saw any fuel in the short time it was running. The injector ohms out correct. Fuel pressure is good also, holds after shutdown. Could the new primary injector at # 6 be questionable?

[XfireZ51]

Looks like I'm going to go with the injectors from FIC. Can anyone suggest which brand of coils I should go with and where to get them.

thanks again everyone,
Big D

My MSDs have been running the motor for 7 years. :dancing
If you are diving under the plenum, may as well swap out the old stuff as a precaution.
Also clean the valley up and drill out the drain hole under the starter. Seal vacuum lines too.

[IMZZ]

You're making me nervous I'm doing the same thing and ordering injectors from FIC this week. Did you call them for advice about the injector? I know it would be a pain but you could swap injectors to see if the problem changes too.

[Paul Workman]

Curious about the current draw/limits for (FIC) injectors, I spoke with Jon (at FIC) briefly about your problem, and he mentioned that there have been cases where customers have inadvertently swapped the primary and secondary injector connectors.

Thinking about that, if your LT5 is NOT modified for secondary deletion, then I would expect what you are experiencing to be the case:


Primary injector not running at idle or little throttle causing a constant miss at lower throttle settings
Bogging when you "step on it"*
WOT works normal (aka "Screams, as you said!)


*With the primary injector in the secondary runner, fuel would not be getting to the cylinder at low throttle due to the SPT plate being closed. However, fuel would back up and pool in the injector housing runner; possibly flooding the runner, depending on how tight the SPT plate seals (and possibly causing other low speed issues too, should the runner fill and run over with fuel to back-fill and spill into the plenum where it would get drawn in by other cylinders...not good!

However, when the secondaries are signaled ON and the SPTs open, initially a slug of raw fuel drops into the cylinder, temporarily flooding it (hence a bog/stutter/miss/blue smoke, etc would likely occur. In a few seconds, the cylinder would pump out the excess fuel and with both injectors now running the engine would perform in normal WOT fashion.

Note: For LT5s modified to delete the SPTs, it shouldn't matter if the injectors are swapped, as they both run full time except at idle, but not having SPT restrictions, there will be no fuel pooling regardless, and it should idle fine, I would think.

If having the two injectors swapped is NOT thee problem, you will need to wring out the wiring/connector to the injector.

It might be easier to pull the plenum than mess with the relay and ECM connector pins, and thereby gaining direct access to the injector itself. Grounding the (black/yellow wire) side of the connector and providing an instantaneous on-off connection to the other side to power the injector, you should hear a audible "click" which would indicate the injector should be working normally...should be.

Page 6E3-A-5 (1990 FSM) is the scematic to help guide your troubleshooting.

Update when you can...

[Big D]

Hi Paul, I also talked to Jon this morning and he said that you had called him. Thank you. He was helpful and gave me the same information. I find it hard to believe that the injector would be bad but i have to check it. So, the plenum is off, again, gettting pretty good at this. The wire bundle is tight and would not allow mis-connection but i checked it anyway, per Jons instructions, and the connectors are to the correct injectors. Jon said to use a 9 volt battery to check the injector and it fired just fine, just like the others that I checked next to the questionable one.
The wire diagram in the manual is not all that helpful, i'll need greater detail now to figure out how to wring out the wiring. Since the other primary injectors appear to be working correctly i'll need to shoot the wire from the injector to the direct ignition housing. The manual just shows all injector wires going to what appears to be one splice or terminal.
and then on to the ignition and the Direct Ignition Housing. It would be helpful if i knew what fired the primary injectors, the manual diagrams don't show that or explain it.

Ken, don't be alarmed, I'm sure it is a vehicle problem and not the injector. Jon is very helpful and understanding. He even offered up a replacement injector before I even verified this one was bad, but i declined the offer. So after my checks above, i feel confident the injector isn't bad and that it is a vehicle problem. The top end run is great, better then it ever was and i contribute that to the new inlectors. But, if i can't find any wiring problems i will have to do the injector swap and see if the problem follows the injector.

[Paul Workman]

Hi Paul, I also talked to Jon this morning and he said that you had called him. Thank you. He was helpful and gave me the same information. I find it hard to believe that the injector would be bad but i have to check it. So, the plenum is off, again, gettting pretty good at this. The wire bundle is tight and would not allow mis-connection but i checked it anyway, per Jons instructions, and the connectors are to the correct injectors. Jon said to use a 9 volt battery to check the injector and it fired just fine, just like the others that I checked next to the questionable one.
The wire diagram in the manual is not all that helpful, i'll need greater detail now to figure out how to wring out the wiring. Since the other primary injectors appear to be working correctly i'll need to shoot the wire from the injector to the direct ignition housing. The manual just shows all injector wires going to what appears to be one splice or terminal.
and then on to the ignition and the Direct Ignition Housing. It would be helpful if i knew what fired the primary injectors, the manual diagrams don't show that or explain it.

Ken, don't be alarmed, I'm sure it is a vehicle problem and not the injector. Jon is very helpful and understanding. He even offered up a replacement injector before I even verified this one was bad, but i declined the offer. So after my checks above, i feel confident the injector isn't bad and that it is a vehicle problem. The top end run is great, better then it ever was and i contribute that to the new inlectors. But, if i can't find any wiring problems i will have to do the injector swap and see if the problem follows the injector.

Do you have an FSM? What year Z is it? I have a 90 FSM, and it shows (referenced page) how the injector is controlled. I'll send the schematic to you, if that will help.

Far as the 9 volt battery goes, Jon said he uses 9 volts instead of 12 to reduce the heating/burning of the little coils inside the injector. However, a 5Ω resistor in series with a lead from your handy 12v battery will do exactly the same thing w/o having to round up a special 9 volt battery. And, that said, I can tell your I've done that test on my injectors "full strength" but just quickly tapping the probe to the injector and pulling the probe immediately away. There's no doubt about it, you can hear that injector's little "click" w/ NO issue, far as damaging the little coil. HOWEVER, using a 5Ω resistor will accomplish the same thing and reduce the current by approx 24% - same current as you'd expect using a 9 volt battery (which as I said: for the short one or two 'taps' to verify the "click" should do no harm either.

Schematic (for a 1990, but essentially the same for other years)

http://i185.photobucket.com/albums/x220/6PPC_bucket/tech%20files/1990%20LT5%20injector%20schematic0002_zps9tqzijn4. jpg (http://s185.photobucket.com/user/6PPC_bucket/media/tech%20files/1990%20LT5%20injector%20schematic0002_zps9tqzijn4. jpg.html)

Essentially, the ECM provides a ground for the pair of relays for each cylinder. However the secondary injectors require further signal from the ECM, via two separate relays #1 (inj. 1+8, & 4+3) and relay #2 (inj 6+5, & 7+2) each controlling two secondary injector pairs.

If the #6 injector checked out (by direct application of voltage) then there is a connection somewhere. Hopefully the schematic will help. (I have another diagram too, and if I can find it, I'll send it too. It might help locate the various connectors and pins for further testing.

Update when you can...

Paul.

[XfireZ51]

Paul,

For purposes of accuracy, the ECM does not actually issue the firing command to the secondaries. The ECM energizes the secondary injector power relays via ground, which in turn powers the secondaries. The secondaries then use the primary injector firing signal. So there is no unique signal coming from the ECM to the secondaries themselves.
Again, another "work-around" from the L-98 avoiding the need for injector drivers on the ECM motherboard.

[cvette98pacecar]

Paul, I do not think you could inadvertently plug a secondary injector plug into a primary injector. The wiring is not long enough. it is hard enough to get the plugs on the injector as it is, I cannot imagine how hard it would be if you crossed the plugs

[Paul Workman]

Paul,

For purposes of accuracy, the ECM does not actually issue the firing command to the secondaries. The ECM energizes the secondary injector power relays via ground, which in turn powers the secondaries. The secondaries then use the primary injector firing signal. So there is no unique signal coming from the ECM to the secondaries themselves.
Again, another "work-around" from the L-98 avoiding the need for injector drivers on the ECM motherboard.

Righto! Poor wording on my part. Better to have said the ECM powers the secondaries via relays #1 and #2, as "explained" by the schematic... (No points for rushing)

[Paul Workman]

Paul, I do not think you could inadvertentlywhatg a secondary injector plug into a primary injector. The wiring is not long .
Though. it is hard enough to get the plugs on the injector as it is, I cannot imagine how hard it would be if you crossed the plugs

Agreed. Swapping isn't my experience either. Jon brought it up, and for what it lacks in probability the symptoms fit the swapping scenario like a glove

Curious to see what actually unfolds...

[Big D]

I have an unmodified 90 and I have the 90 SM. I went to the library and got a diagram for the primary circuit which shows the primary wiring and the "splice S127" i believe. I also have the LT5 Fuel and Emissions Course book which is somewhat helpful. Not sure what my next step will be, was thinking turning it over and checking to see if i am getting voltage to # 6 at the injector. Shouldn't take but a couple of turns to verify. From the schematic it looks like i should be looking for a ground from the ECM on terminal A of the injector. Since i can shoot the wire from the yellow ECM connector to the injector and it is good I should be able to look for the ground on the back of the ECM while i turn it over, doing this would also NOT fire the left bank injectors since I haven't removed their electrical connectors, thus avoiding sending fuel into the cylinders. Also will check for 12 volts on the B side of the injector with the key on. Hope to look at this tomorrow if the chores don't overrule.

[Big D]

I have an unmodified 90 and I have the 90 SM. I went to the library and got a diagram for the primary circuit which shows the primary wiring and the "splice S127" i believe. I also have the LT5 Fuel and Emissions Course book which is somewhat helpful. Not sure what my next step will be, was thinking turning it over and checking to see if i am getting voltage to # 6 at the injector. Shouldn't take but a couple of turns to verify. From the schematic it looks like i should be looking for a ground from the ECM on terminal A of the injector. Since i can shoot the wire from the yellow ECM connector to the injector and it is good I should be able to look for the ground on the back of the ECM while i turn it over, doing this would also NOT fire the left bank injectors since I haven't removed their electrical connectors, thus avoiding sending fuel into the cylinders. Also will check for 12 volts on the B side of the injector with the key on. Hope to look at this tomorrow if the chores don't overrule.

[Big D]

Ok, the saga continues. First, I believe I have found the problem but ran out of time last night to fully verify. Looks like I have a bad connection at the ECM connector, probably a pushed back socket at A8 or I oversized it so that the pin doesn't make good contact. Now the story. First I disconnected the electrical connectors from all of the injectors. Then, using a 9 volt battery, I checked the # 6 injector and the # 2 injector as a knew the # 2 was good. I jumpered from the injector to the battery negative side and then touched the positive side and got a good click each time. Did the same to # 2 for comparison and it acted the same, so I ruled out a faulty injector (which I basically had already). Next I pressurized the fuel rail and did the battery check again. Looking down the injector port you can see the injector spray end and tapping the positive produced a nice spray out of the #6 injector, same with # 2, again verifying the good injector. Then I re-connected the plenum electricals for my next test. With the ignition module now connected I reconnected the #2 and #6 injectors electrical connectors. I had my assistant (daughter) turn the car over while I looked down the injector port. # 2 sprayed very nicely but #6 did not. So, back to shooting wires. Checked wire from injector to ECM, no problem. Looked into the ECM at pin 8, .7 K ohms. Re-connected the yellow ECM connector. Then I did voltage and ohm checks of each injector connector pins. With the key in the run position, "B" side should read around 12 volts (from the ignition) and the "A" side is looking for a ground into the ECM. I'm assuming here from data I have generated that the "A" side should read about .7 - .8 mega-ohms in this setup. (all "A" side resistance was around this number except for # 6). # 6 showed an open circuit on the "A" side but 12v on the "B" side. Ok, so the "A" side is not getting the signal from the ECM. Removed the yellow ECM connector and re-verified continuity between it and the #6 injector and it was good. Verified .7 k ohms into the ECM at pin 8 and it was good. Checked other injector pins into the ECM and got the same results. Next I jumpered from pin 8 of the ECM to socket 8 on the connector. Went to the injector connector and ohmed out pin "A". It read .7 k ohms. Then I was out of time. I will try and "fix" the socket to get a better connection with the pin and then do the injector test like before. I feel pretty confident right now that the plug is the problem. I'm thinking I might have used a test pin into the connector that was too large when I was first doing my injector tests when this problem first surfaced and the larger pin opened up the socket too much. Will get back at this next weekend, hopefully with good results.

[tccrab]

Boy, talk about deja vu.
I had this EXACT problem a few years ago for the EXACT same reason.

http://www.zr1.net/forum/showthread.php?t=10828

I seem to recall that I bought extra connectors, I'll go dig through my big box 'o spares.
PM me your address I'll mail you a couple, gratis.
I don't have the OEM crimp tools, I had to borrow a set from a former member. If you're careful you can get the job done with just a regular set of pliers.

'Crabs

[Big D]

thanks 'Crabs, I'm hoping to get back on it this weekend and see if I can't get her back on the road, missing all this good weather we are having up in the Pacific N'West. I gotta keep the chores at bay though.

[Paul Workman]

I'm thinking I might have used a test pin into the connector that was too large when I was first doing my injector tests when this problem first surfaced and the larger pin opened up the socket too much. Will get back at this next weekend, hopefully with good results.

IIRC, there was a post (by Marc Haibeck??) a year or so back warning about that very thing: be very careful NOT to shove a pin (such as on a VOM probe) into those connectors as over expanding the cylinder (female side) of the connector is a common problem.

:happy1:

[tccrab]

IIRC, there was a post (by Marc Haibeck??) a year or so back warning about that very thing: be very careful NOT to shove a pin (such as on a VOM probe) into those connectors as over expanding the cylinder (female side) of the connector is a common problem.

:happy1:

Ayup.
I remember reading it and saying to myself, "BOY, I sure wish I had read this FIRST!!!"

'Crabs

[Big D]

I did read it and I thought I had picked the correct size pin to insert into the socket but obviously I must not have. Hopefully this will fix this problem and I can move on. Thanks to all for all the help, previous postings and information.

Big D
69 L46/M21
90 ZR1

[RussMcB]

Good job, you guys. I'm impressed you were able to track it down methodically.

And I guess the lesson here is, whenever you have a problem read the entire contents of ZR1.net and you'll find the answer. :-)

[Paul Workman]

I did read it and I thought I had picked the correct size pin to insert into the socket but obviously I must not have. Hopefully this will fix this problem and I can move on. Thanks to all for all the help, previous postings and information.

Big D
69 L46/M21
90 ZR1

I give you "cudoes" for breaking this down in logical steps. I think you'll get along with this car just fine!:dancing

[Johnny5]

i have the same hesitation/miss at low acceleration, idle is fine and WOT is great, I changed coils, FIC injectors and 6 spark plugs. LMK what you find. Istill nee to chznge the back 2 plugs so im hoping thats it.

[IMZZ]

Johnny5 you can try to isolate if it is one of the back cylinders by pulling a plug wire like BigD did in post #20.

[Big D]

IMZZ, have you done the injectors yet? I got my de-pin tool and the sockets from 'Crabs today so hopefully i can get to it this weekend and get her fixed. Thanks 'Crabs for the sockets and info, should be able to handle it, very similar to aircraft connector repair.

Big D
69 L48/M21
90 ZR1

[Johnny5]

Johnny5 you can try to isolate if it is one of the back cylinders by pulling a plug wire like BigD did in post #20.

Thanks IMZZ I have to get around to it. She runs great at WOT so thats 98% of what I drive it at

[Paul Workman]

Food for thought...

After I first got my Z, it had a slight "miss" on one cylinder that wasn't so apparent under heavier throttle - if much at all. Turned out to be a burnt valve, stemming from a weak primary injector!

Just sayin.....

[Johnny5]

I replaces my injectors when i first bought it, all coil packs, wires, and 6 spark plugs. The bog is iccasionally only under slight throttle. Hopefully its a plug i havent changed.

[IMZZ]

IMZZ, have you done the injectors yet?

I got my injectors on Saturday. I'm trying to clean and restore everything before I put it back together. There is sure a lot of things to remember to do when putting these back together. I am trying to source a weatherpack seal that I believe was missing from previous work. I'm hoping to get it running by the weekend.

[Johnny5]

Food for thought...

After I first got my Z, it had a slight "miss" on one cylinder that wasn't so apparent under heavier throttle - if much at all. Turned out to be a burnt valve, stemming from a weak primary injector!

Just sayin.....

Thats scaring me. I have to get some universals together to changevthe back 2 plugs and pray that it was an old plug causing it

[XfireZ51]

Watch this video. Some things sound familiar, maybe?

Also very interesting comments in this vid regarding effect of oil in throttle body


http://youtu.be/Mk4e5XFe47A Go to 5:06

[Big D]

I got the swivel socket from NAPA and it works great getting the back two plugs out. It is easy with a swivel. Hope the plug is the problem.
I'm still chasing gremlins in mine. When I shoot back into the ECM, #6 injector pin is showing 86 k-ohms while the others are showing .97 - 1.0 m-ohms. Not sure if that makes a difference since I wasn't able to check to see if the injector is working; two person job and my assistant was working last weekend, one to turn over the car while I look down the injector housing to check for fuel spray. Hopefully I will be able to check it this weekend.
By the way, anybody out there have a good schematic/diagram for the ECM, or know where I can get one? Would sure help in troubleshooting.

Big D
69 L46/M21
90 ZR1

[XfireZ51]

I got the swivel socket from NAPA and it works great getting the back two plugs out. It is easy with a swivel. Hope the plug is the problem.
I'm still chasing gremlins in mine. When I shoot back into the ECM, #6 injector pin is showing 86 k-ohms while the others are showing .97 - 1.0 m-ohms. Not sure if that makes a difference since I wasn't able to check to see if the injector is working; two person job and my assistant was working last weekend, one to turn over the car while I look down the injector housing to check for fuel spray. Hopefully I will be able to check it this weekend.
By the way, anybody out there have a good schematic/diagram for the ECM, or know where I can get one? Would sure help in troubleshooting.

Big D
69 L46/M21
90 ZR1

Not sure why you'd want a schematic. The pinouts are available in the FSM which I assume is what you really need.

[Big D]

With the schematic/diagram I can trace the circuit inside the ECM to see what controls the injector and if I find that the ECM is causing my problem I can hopefully determine if the internal circuit is replaceable or repairable. W/O the schematic/diagram I haven't a clue.

[XfireZ51]

With the schematic/diagram I can trace the circuit inside the ECM to see what controls the injector and if I find that the ECM is causing my problem I can hopefully determine if the internal circuit is replaceable or repairable. W/O the schematic/diagram I haven't a clue.

Just my opinion, but you are quite a few steps from having the ECM as the culprit.

[tccrab]

Just my opinion, but you are quite a few steps from having the ECM as the culprit.
I agree.
Re-pin the connector with the pins I sent you.
Try not to overthink this.
It's not totally inconceivable that you might have a bad ECM, but you won't know for sure until you fix the pins first.
I made the same mistake.
Took me over 3 years, more cash than I'll ever tell wifey about, untold stress and aggravation to finally nail it down.
And truth be told, I'd likely never have found it if it wasn't for this Forum.
The Brotherhood of the Beast is alive and well.


'Crabs

[IMZZ]

Any luck? I finished my injector/plenum job. Everything came out OK. I just had to decide when to quit cleaning or fixing things. I wanted to be able to enjoy it this summer and remember that winter is coming.

[Johnny5]

my father changed the back 2 plugs the other day and it runs great now. Not a damn problem.....except my bose radio lol Did you ever find out why your lt5 is missing? I am curious

[Johnny5]

Food for thought...

After I first got my Z, it had a slight "miss" on one cylinder that wasn't so apparent under heavier throttle - if much at all. Turned out to be a burnt valve, stemming from a weak primary injector!

Just sayin.....

Hey Paul it turns out it was just my plugs, but what did you do to fix your valves. Were you able to buy a single valve? did you have to buy a whole head? and where could you even purchase valves or a head?

[Johnny5]

Ok everyone, Got the plenum off with no problem. Way easier then what I had imagined with all the good info on the Registry. Took about 40 minutes and broke nothing. However, I tried a suggested method for anti-freeze removal, just drain the plenum, and I would not advise that method. After releasing the plenum, antifreeze began bubbling up from the two holes in the injector housing. Plugged the holes quickly and then drained the radiator. Saving ten minutes at first cost me hours in cleanup. Dang, I hate antifreeze. The valley was extremely clean, prior to the antifreeze dump and all connectors and hoses are in very good shape. Well, at least I know the valley drain works just fine.Tested the wires and they come in at 7.5-9 K ohms for all, well within spec. Also checked the coils, all 4 coil resistance within spec. Also did a visual of the coils and they all look good, no signs of heat deterioration or cracking so I am going to let them go and just change out the injectors. I may end up regretting this decision but I was going to go with stock coils anyway so I don't see the advantage at this point. This is a very low mileage car. Looking forward to installing the new FIC injectors and getting her back on the road.

Big D
69 L46, M21
90 ZR1
95 Suzuki 1200 Bandit
2014 Triumph Thruxton

Working with Jim Wazoo Leader he had a coolant suction tool. It is very useful. His hooks up to an air compressor which is cool but I don't have room in the garage for that if I pull the plenum with the car in there so I bought the same thing but it is a manual pump and you can reverse it and put the coolant back in. Pretty neat and handy for plenum pulls. I bought mine for $80.

https://www.google.com/shopping/product/17688988214874175952?q=powered+liquid+extractor&rlz=1CAACAG_enUS605US605&espv=2&biw=1366&bih=633&site=webhp&bav=on.2,or.r_cp.&bvm=bv.99261572,d.dmo&ion=1&tch=1&ech=1&psi=KIy8VZTVMoure-j8vagG.1438420009160.5&prds=paur:ClkAsKraX-z1Ek40oaLKYEsIIiimRSLQk0qhQrCYmnNvHZh-_Gd5m_gXhLRJhc_WDmSorqLSdebxs6Cm67LYbTW3oSoRQHtfV5 QQAnimi-1YwsOVtRKIPjknNxIZAFPVH739TNuWvw70NGUXME9dV__AXuYs 9g&ved=0CAwQpitqFQoTCPaElqDEh8cCFcWZHgod4b8FIQ&ei=UIy8VfacF8WzeuH_logC

[Big D]

my father changed the back 2 plugs the other day and it runs great now. Not a damn problem.....except my bose radio lol Did you ever find out why your lt5 is missing? I am curious

Nope, still chasing it. Haven't had a chance to get back to it because the Blazer decided it liked to shift into 4WD all by itself so I've been playing with that with my free time. Looks like a TCCM problem.

Still is pointing to the ECM with the big difference in resistance between #6 and the other 7 pins into the ECM. Not yet willing to shell out the $300 or more to experiment.

[Johnny5]

Nope, still chasing it. Haven't had a chance to get back to it because the Blazer decided it liked to shift into 4WD all by itself so I've been playing with that with my free time. Looks like a TCCM problem.

Still is pointing to the ECM with the big difference in resistance between #6 and the other 7 pins into the ECM. Not yet willing to shell out the $300 or more to experiment.

My father owned a 96 jimmy and a 2000 jimmy and did all his work himself. PM me with your number and im sure he could point you in the right direction

[A26B]

Hey Paul it turns out it was just my plugs, but what did you do to fix your valves. Were you able to buy a single valve? did you have to buy a whole head? and where could you even purchase valves or a head?

Pay us a visit & see what we have. ;)
www.jerrysgaskets.com

[Paul Workman]

Hey Paul it turns out it was just my plugs, but what did you do to fix your valves. Were you able to buy a single valve? did you have to buy a whole head? and where could you even purchase valves or a head?

Replacing a valve in an LT5 requires the motor to be pulled to facilitate the cam phasing, etc., after the valve(s) are serviced/replaced. So, I opted to complete my porting at that time as well.

As it happens, I had a porting mishap resulting in replacing one head out of convenience; a "do-over", if you will.