Knowledgeable Tech -Starting/Performance problem needing assistance

[zr1don]

If the 11 in "vacume" you referenced is the MAP sensor reading at idle, that is normal, something around 18+ in of idle vacume.

[sjs]

Originally Posted by zr1don

Idle vacume should be 18 - 20 in, inj pw at idle should be around 4 ms, idle fp should be around 46, 39 is definitely low.

Thanks, you don't happen to know about cranking vacuum and ms do you ?

[sjs]

Thanks ZR1Don for the info, no the reading is 11in of guage vacuum not scanned ... although this was at a rough idle seconds before it died. I am starting to wonder again about cam timing slippage, but I suppose I had better check my injectors first ... just hate to take the motor apart twice! Also sorry about the spelling, the later it is the worse my spelling is !
Thanks for the help.

[Paul Workman]

Originally Posted by tccrab

At 100k miles I'm willing to be that it's already had the injectors replaced.
That being said, it could still be bad injectors, especially if the previous owner had them replaced with more of the Multecs.
Check the MAP hose first as Jerry said above.
Maybe one of the Brotherhood local to you wouldn't mind meeting with you for a semi-educated diagnosis.


TomC
'Crabs

BINGO!

That is what happened on mine. The injectors were replaced with more of the same (GM dealership before I bought it). They crapped again as well. The new Accels made and incredible difference in overall operation, and especially at idle!

And too, as pointed out, the fuel pressure situation has to be resolved first. That issue alone can be the root of a lot of evil.

To the OP: the O2s are not going to come into play until the thing warms up some, but once you get to that point where it goes into "closed loop" mode, you might want to compare integrator values and O2 cross-points. First thing tho...is that fuel pressure issue!

P.

[lbszr]

Was the fuel pressure monitored while it was trying to run, or with the key on? It might be falling even lower than 39 while it's running.

[sjs]

Originally Posted by Paul Workman

BINGO!

That is what happened on mine. The injectors were replaced with more of the same (GM dealership before I bought it). They crapped again as well. The new Accels made and incredible difference in overall operation, and especially at idle!

And too, as pointed out, the fuel pressure situation has to be resolved first. That issue alone can be the root of a lot of evil.

To the OP: the O2s are not going to come into play until the thing warms up some, but once you get to that point where it goes into "closed loop" mode, you might want to compare integrator values and O2 cross-points. First thing tho...is that fuel pressure issue!

P.

Thanks, am working on the fuel psi right now ... will let everyone know

[Kevin]

you can check if the injectors are good with an ohm meeter. good ones should be between 12.5 and 15 ohms

[sjs]

Well, I did learn the why the psi was a little low ... fuel filter wasn't that old but it was restricted some ... also pulled the pumps to see if they were both okay and found a cracked hose ... not bad but cracked. This did help the psi and it stays steady at 48 psi at all times. So this is good news, easy fix ...!!!

Now for the bad news , injectors still don't leak down but car still won't really run. I don't have to worry about closed loop or cross counts ... car wont stay running over 30 seconds ... period. Will restart but dies again.... am going to have to assume the injectors are bad as everyone mentioned them ... only thing that bothers me is that I have seen cars with 2-3 bad injectors run better than this ... I have a hard time buying 3-4 went bad all in the same 5 min trip ?? But you never know ... will replace them and see if it runs ... if it doesn't my ZR-1 experience may not be a good one! But either way I sure like the car ... just frustrating as I don't have time right now for major surgery .... wife's daily driver has needed a wrist pin for 6mo now .... no way she will like tearing this down first if the injectors don't cure it. Hope they do! Thanks to all for the advice!

[Paul Workman]

Originally Posted by sjs

... injectors still don't leak down but car still won't really run. I don't have to worry about closed loop or cross counts ... car wont stay running over 30 seconds ... period.

only thing that bothers me is that I have seen cars with 2-3 bad injectors run better than this ... I have a hard time buying 3-4 went bad all in the same 5 min trip ??

Yeah...I'm dubious too, far as injectors causing this severe of a problem goes. Sounds like we need to put the anecdotal suggestions in their place and begin with the basics; a methodical elimination process.

Note: When it's time to get down to brass tacks...like now...I always like to establish a solid base - deductive reasoning, if you will - working toward discovery in a logical, progressive manner. Its sort of like painting a wall by beginning at one end and working toward the other instead of a random swipe with a brush first here and then there until the wall is covered.

However, by reading the posts for a few years, my unscientific survey says 90% of the LT5 gremlins reside under the plenum: The problems seem to center around (1) the OEM injectors, (2) secondaries, (3) starter solenoid contacts, and (4) coil packs...in that general order. Address them all while under the plenum on the first visit and one can be very confident of the LT5 after that for some time to come. So, I sometimes chose to R&R certain things just to head off potential near-term problems - regardless of whether they are causing the current problem or not; I'd rather be driving than wrenching, if you know what I mean.

A preliminary question: Water in the fuel? That is worth eliminating before going on...Just a thought. (We had that issue here locally with one of the Shell stations last winter. Messed up a bunch of cars here in town for a week or so till the problem was discovered and rectified.)

At this point I would like the peace of mind that she's not suffering a mechanical malady. A compression check would clear the air - far as a gasket or cam timing goes. And, we get to look at all the plugs for clues in the process!

With all the plugs pulled and having a fully charged battery and a full blown battery charger on the battery (i.e., no trickle charger, but one capable of maintaining full charge between cylinder tests), and having the accelerator to the floor (anti-flooding mode kills power to the injectors when rpm is below normal idle speed), crank it for 5 compression strokes (rest of plugs removed) and see what it reads. For comparison, compression on my LT5 was 180# at one time, and after my porting and cam re-timing it was 220, FWIW. Uniformity (w/in say range of 10#) from cylinder to cylinder and side to side, being the point. And, apparently compression can range between 180 and 220#, depending on circumstances.

I'm going to guess (hope) mechanically it checks out, yes?

BTW, how did the plugs look? Were they or some of them wet with fuel? Or, were they dry? Any of them look "steam cleaned" as compared to the rest? Water (as in water in the fuel)? Coolant? (probably not if the compression check went well).

I'd want to pull the connectors off the back of the ECM one at a time and do a mechanical/visual inspection, just to be sure all the pins and sockets are clean and not out of position before reconnecting them. And same goes for the throttle position sensor connection (driver's side of the throttle body) and the IAC motor (opposite side). I'd like to eliminate any issues with the cam and crank sensor connections too. Might look at the O2 connectors too, while you're down there...again, just eliminating connection stuff as we go...

To complete the visual inspection, the plenum has to come off. Pulling the plenum is like a "right of passage" for LT5 drivers. It is a bit intimidating looking at it from the first time. But, after you've done it once, it boils down after all to just some screws and connectors and throttle cables. The biggest PIA is draining a few quarts of coolant and refilling after putting it all together. (And, THAT can be eliminated too, if plugs are installed in the injector housings that lead to the TB coolant lines! The plenum runs much cooler and pulling it for any reason becomes a 15 minute job after that!)

So, a visual inspection of all six electrical connections; 4 on the plenum and 2 on the coil packs are in order. Nothing burnt or cruddy/corroded or wet? Plug wire connections and wires in good shape?

You may need new injectors, but I agree w/ you, far as the suddenness & severity of the symptoms go; the symptoms are too sudden and too severe to suggest injectors as the issue. Not to say you don't have an issue there, but just that the current circumstances suggest the bigger issue is elsewhere at the moment. So, it wouldn't be wrong to table the idea of replacing injectors just now - far as strict troubleshooting procedures go. However, if they are the OEM Multi-techs, I'd be wanting to replace them before reinstalling the plenum. (But, that's just me.)

With a couple alligator clip at each end of some (zip) wire leads, you can visually test the individual injector operation mechanical function and spray pattern.

Push in on the wire spring retainer loop and lift the plugs off of the injectors. Then attach one alligator clip to one of the spades on the injector. Turn the ignition switch to the on position to activate the fuel pump(s) momentarily. No fuel should be leaking on any of the injectors. Then with the other end of the wires connected to the +/- sides of the battery, you can tap the other alligator clip on the remaining injector post, listen for a clear "click-click as it opens and closes, and observe the spray patterns to check for uniformity.

Note: Even with new injectors I recommend doing this procedure to insure (1) none of the injectors are leaking, and (2) that they all work uniformly...ask me why.

Now we're looking at the coils. I'd want to compare the resistance across the plug wire posts of each coil and to ground. True, a VOM is not going to detect a high voltage (insulation breakdown) issue, but it will detect an anomaly if there is one - and there shouldn't be. Finding an anomaly is grounds for replacing the coil(s). If it is possible to test something, I never recommend replacing it for replacement sake. But, because proper testing is not within the capability (of my equipment), replacing them...may not be wrong at this point. Your choice.

Just for grins, are the injector housing bolts all at 20# of torque? If not, pull the bolts and put some blue Lock-Tite on them and re-torque them, starting from the center and working your way (in turn( out to the ends of the housings in simultaneous fashion.

Again, being you have the opportunity - plenum removed and all - now too would be a dandy time to verify the operation of the secondary system. (See Marc Haibeck's site for the procedure as to which wire to ground at the ECM connection to actuate the secondary vacuum solenoid switch.) (Or, depending on your emissions requirements, removing or tying the secondaries open could be done now, in conjunction with a chip configured sans secondaries - forever eliminating that system from becoming an issue at some point.)

One last thing to consider while the plenum is off is pulling the starter and inspecting the contacts and the copper ring on the solenoid that connects the battery with the starter armature. An emery board will go a long way to refurbishing the copper ring - removing pits and carbon and the like, as well as shining up the mating surfaces on the contact posts as well. A very light smear of grease on the moving parts would be a good thing too.

By now, if nothing has been discovered amiss, it may be time to reinstall the plenum and hook everything back up and see if the symptoms persist. If so, and without further indications of something not right - the scan isn't offering any clues, e.g., MAP sensor or the like, I wouldn't know what next to try but to borrow an ECM and compare. There's only one other electronic piece, the DIS, which is also under the plenum. But, if it was at issue there should be codes, and you have none indicating the DIS is bad (and according to gurus, they are rugged little bastards and seldom fail).

My sense of it is that something in this procedure should ferret out something useful, sans anymore help from the scanner.

Get back when you can. Maybe one of the Brothers nearby can lend you a hand. Sure would like to know what it is.

P.

[XfireZ51]

You say you are showing a lean condition and a secondary fault code? Vacuum leak somewhere? 7.5ms sounds like a LARGE PW for idle. But a lean condition may call for that and flood the motor. What do the plugs look like? R they wet? If you put a scan tool on it, just turn the ignition to ON and scan for the different nominal sensor values. Make sure each sensor is reading normal at 0 RPM ie MAP 97-100kPa depending on location, O2 .450v, CTS, MAT, etc. Check connections to ignition module. Did a critter gnaw on a wire?