LT5 miss at all speeds - Page 3 - ZR-1 Net Registry Forums

XfireZ51 · 07-17-2015

Quote:

Originally Posted by 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

My MSDs have been running the motor for 7 years.

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 · 07-17-2015

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 · 07-17-2015

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 · 07-17-2015

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 · 07-17-2015

Quote:

Originally Posted by 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.

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)

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 · 07-17-2015

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 · 07-17-2015

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 · 07-17-2015

Quote:

Originally Posted by 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.

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 · 07-17-2015

Quote:

Originally Posted by cvette98pacecar

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 · 07-18-2015

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.

07-17-2015	#22
IMZZ Join Date: May 2015 Location: Oregon Posts: 32	Re: LT5 miss at all speeds 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. __________________ Ken "IMZZ" 1991 ZR-1 Corvette 1990 MX-5 Miata

07-17-2015	#23
Paul Workman Join Date: Nov 2007 Location: Squires (near Ava MO in the Mark Twain N'tl Forest) - Missouri Posts: 6,493	Re: LT5 miss at all speeds 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... __________________ Good carz, good food, good friendz = the best of timez! 90 #1202 "FBI" top end ported & relieved Cam timing by "Pete the Greek" Sans secondaries Chip & dyno tuning by Haibeck Automotive SW headers, X-pipe, MF muffs Former Secretary, ZR-1 Net Registry

07-17-2015	#24
Big D Join Date: Jun 2014 Location: Washington state Posts: 17	Re: LT5 miss at all speeds 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.

07-17-2015	#26
XfireZ51 Join Date: May 2007 Location: Chicagoland, IL Posts: 9,664	Re: LT5 miss at all speeds 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. __________________ [SIGPIC][/SIGPIC]Former Membership Chairman Former ZR-1 Registry - BOD 1972 Corvette 4speed base Coupe SOLD long time ago 1984 Corvette Z-51/4+3 SOLD 1992 Corvette ZR-1 Aqua/Gray #474 SOLD 1992 Corvette ZR-1 Black Rose/Cognac #458 2014 Honda VFR Interceptor DX

07-17-2015	#27
cvette98pacecar Join Date: May 2011 Location: Sydney, Australia Posts: 2,479	Re: LT5 miss at all speeds 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 __________________ Robert J. DeMarco [SIGPIC][/SIGPIC] [COLOR=blue]G[/COLOR][COLOR=red]rand[/COLOR] [COLOR=blue]S[/COLOR][COLOR=red]port[/COLOR] Registry Lifetime Member NCM Lifetime Member #2655 Pacecar Registry Member [COLOR=red]ZOOM Charter Member - ZR-1 Owners of Michigan[/COLOR] [COLOR=plum][I]ZR-1[/I] Registry member since 2012 [/COLOR] [COLOR=black]1990 LPE "368" Aerobody ZR-1, Last ZR-1 built by John[/COLOR] 1991 Callaway Aerobody ZR-1, DRM 500 1991 Shinoda Aerobody Spyder, 1998 Pace Car

07-18-2015	#30
Big D Join Date: Jun 2014 Location: Washington state Posts: 17	Re: LT5 miss at all speeds 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.