Sounds downright queer to me. Maybe it needs to be blown out. Give it a good spanking and see what happens.

I have no idea... I beat on it like a red headed step child... even threatened it - never did that before... and nothing helped.

Got to the 101 freeway, and it just smoothed right out. As smooth as it as ever been. Absolutely amazing.

Now... what will it be like when I go back? That's any ones guess.

Did you reset the ECM, or in other words, was the battery disconnected while you were working on the car?
The stored ECM values could have been so far off, that it takes a small relearning effort to get in line for the good stuff.
The values in TunerPro showed lean, but the ECM was dumping a lot of fuel, making it actually way rich. When diagnosing this stuff, you often got to think around corners.

You might just needed to get the cat and O2 up to operating temperature to clear off the excess fuel.

Sure sound strange. Good luck for your way home!

yes, battery was out of the car... for two days!

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yea, the FSM notes that.

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ECM finally getting sorted out with all the repairs?

** Edit ** - Or maybe the new 02 sensors getting burned in?

I am not sure... that was one long 15 miles... took over an hour of stop and go.

Which might be the issue... I was going no more than 10-15mph for a major chunk. It smoothed as soon as I got to some highway speeds again.

And yes, new O2s coming on line... hard to say.

ok... getting ready to hit the road! I will report ASAP!

Dude I have watched your threads about this crazy freakin problem for a while now. I'm sorry that I don't have anything useful to add about fixing it....

I really hope you get it sorted for good.
Will

Well... it started out a-ok... then when to shit... and varied in degrees of shit... then kinda smoothed out, but still spark knocked.

All 8 injectors feel like they are firing, getting ready to test them and check for spark.

It is really feeling like a huge ass miss now.

Well?

I am at my wits end.

It's backfiring... it's running like shit...

It will kinda hold an idle...

So... a few random thoughts:

Timing chain? Could it have worn out, jumped a tooth? eaten a tooth?

I have the LTCC, but it seems to be working ok... It will throw its own codes, but I have to get into and monitor it.

I am a total loss... tonight:

SERIOUS backfires... All plugs show spark (both the old way to pulling a wire and by using a timing light to detect a firing.

All injectors are ok, between 17.3 and 18.2 ohms. These are new matched Bosch III units from FIC, about a year ago I installed them.

Tomorrow, I will run another datalog...

I was just reading my Helm Manual... and the section for "Symptoms" is rather tragic, my car has all of them.

At the same time.

whimper.

Oh, wait, I don't have dieseling, exhaust odors or poor fuel economy... YET. The MPG isn't something I track on a daily basis, so it could be sucky and I wouldn't know it.

One interesting tidbit...

Tonight, whilst debugging, I started it, and it sounded great (oh, great how am I going to diagnose when it's running ok), I then started to move the car, with the brake on, and it all of a sudden started to run like crap again... load flat out kills it.

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Nope, it would run like crap all the time.

Good luck.

This is sounding more and more like an electrical problem, LTCC/ECM but switching the ECM didn't help, right,

sure sounds like a fuel problem . maybe some foating things in either your tank or fuel rail .our cars being over 20yrs old deposits can build up . you might want to clean every thing including fuel lines . just a thought .

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Hmmmm. Symptoms would make me think ignition BIG time.

Luck man.

Thursday, I am going to tear into the LTCC install. Check the harness, top to bottom, make sure all is clean and nothing is pinched/cut.

Confirm all solder joints are good and such.

I put the LTCC brain down under the overflow tank, in the inner fender. It needs to be in a cool spot, and it is. When I touched the case, it was at air temp down there.

I have an email into the guy who designed it...

Bill - what grease should I use on the harness again?

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Could you make another log file and see if it's still lean?

You might also want to try to get some action from the brake in your recording and see if depressing the brake will increase your lean condition.

If it's still lean, I'd think your on to something with the fuel pump. When ordering, don't forget to order a new strainer, Delcos come without it.
Take a look at the fuel lines prior to ordering, though.
Maybe the pulsator slipped off slightly?

Where is it actually backfiring, plenum or exhaust?

Good luck, man.

Exhaust is back firing. So much so that I saw fire.

I won't be doing a log today. I am using the Jeep... I don't want to risk any major mechanical damage to the Vette. I can do a log around town tomorrow and do it in a more controlled environment, closer to home.

I think fuel might be it... I suspect it is still uber lean... all the behaviours and symptoms are 100% identical. Instead of being hit/miss, they are pretty much 100% of the time... in short, it's getting worse and not better.

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Well, I've said (and was told by my company's engineering) that dielectric grease was non conductive and for dry circuits (under a half amp), to use a contact lube.

That being said, the major brands say use it on contacts, bulb sockets, everything. The debate will go on.
See the links below. Interesting youtube vid that flashes a sign in the beginning that says "we now think dielectric is nonconductive and will have a new video out".

What I will do from now on is to use dielectric on the boots/plastic of harness connectors but leave any gold contacts dry (gold will not corrode). And obviously on plug boots. I wouldn't be real concerned using it on tin plated contacts (trailer connectors) or lightbulb sockets,etc.

But, I'll still use Vasoline on the battery terminals and ground cable to frame connections because it's worked for me for many years.

http://www.permatex.com/documents/tds/Automotive/22058.pdf

http://www.permatex.com/documents/tds/Automotive/31824.pdf

https://tds.us.henkel.com//NA/UT/HNAUT ... 000D946/$File/DIEG-EN.pdf

http://www.crcindustries.com/files/ElectronicsGrease.pdf

http://continuouswave.com/ubb/Forum6/HTML/002410

http://www.youtube.com/watch?v=8W7o-CRRmGo

Cool! I just wanted to be anal about this... THANKS!!!!

Current status and specifications of issue:

I thought it would be a good idea to sit down and update the problem and summarize the specs of my car.

Specs:

1992 LT1/MN6, 180k miles

Engine - internally stock and original

Ignition - LTCC; uses a brain box to intercept Opti commands and fire one of 8 GM (Denso made) coil8 from an LS1. System was installed Oct 2003 and has shown to be very reliable. Only issues have been related to the harness (bad insulation on solder joints or belt explosion tearing up harness). This system has never shown failure.

DynaSpark Opti, without cap/rotor. New last year due to warrantee claim. Prior unit failed; tone disc was bent and rubbed the optical sensor until damaged. H16 resulted, similar driviblity issues.

Sensors: All stock or stock replacements. Knocks new May 2011, O2, new Bosch, this week. All others of varying age. I have a new PCV, need to install.

Vacuum lines: All present and snug. Have small clamps to install.

Air Filter: K&N, does need a cleaning.

Plugs: New NGK Platinum

Wires: Taylor universal, I made them to fit. 2 years old

Exhaust: Newer (60k) exhaust manifolds with copper gaskets, all torqued, new bolts (no studs) holding cats to collectors, Corsa cat back. Cats were used, from a CF'r, bought about 4 years ago with 15k miles on them. NO EXHAUST LEAKS UPSTREAM OF O2 SENSORS! First time in several years, actually... sounds nice when it's running well. Very quiet.

Fuel Pump - newish, about 3 years

Fuel filter - New in May 2011

Fuel Injectors - New (18 months) from FIC, Bosch III injectors. All ohmed between 17.3 and 18.2

Tested spark, all coils seem to be firing ok.

Swapped ECM's, no change. Same stock chip.

EGR replaced 9 years ago. Will test.

With all the recent repairs, nothing has fixed it. Depressing doesn't even come close..

Symptoms:

Spark knock, back fire, sluggishness, constant miss, generally poor drivablity.

This problem has been coming and going since May. Initially, I thought it was bad gas, and treated accordingly, and it went away. I added a couple of cans of SeaFoam and that seemed to fix it... I will say that the engine has felt soft on power, but running smoothly.

It came back, and that time, about 3 weeks ago, it has been getting progessively worse and worse.

Fuel pressure appears ok; 40 PSI at idle, jumps up 2 or 3, drops to 38... It seems low, nut not insanely so.

I hope this reboot will help us come to terms with this and fix it. I have an email into LTCC guy, Bob, and hopefully he will see something we have missed.

Only funny sounds are from the dual mass flywheel jerking around when the engine runs like crap.

Immediate plans:

Chase LTCC harness. Confirm it's ok.

Inspect all grounds underhood and on engine block.

New fuel pump, strainer and filter.

Clean air filter.

Test EGR valve.

Random Commentary:

Back in the mid-80s, my brother had a then new Thunderbird. 3.8l V6, very nice car. It either ran fab or ran shit. And there was no warning. The dealer could not trace it and it was very random. I suggested then that it was either a ground or vacuum problem... but it was under warrantee and I never touched it (good choice, why ruin warrantee and lose complaint rights?). I am going with that approach, too.

EGR has been discussed... Honda had issue when the EGR injection ports in the intake would clog. These ports, about 3mm, would carbon and block up. This would cause an at cruise stumble and on OBDII cars, a code. The fix was to pull and tank the manifold to clear the ports. My problem has transcended this.

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This is good for folks who either a) have't followed the entire thread or b) don't know you and your car well.

Do you have Probst's "Corvette Fuel Injection"? If not, I'll poke around the LT1 portion I've never touched and see if I can find anything useful.

I do have that book... I wish Charlie was still alive, I would so be in touch with him.

thanks for the props... it struck me as logical after all this time.

gosh what a pain . jmho. but to me it sounds like there is some trash in the fuel system somewhere . could also have a couple injectors that are partially clogged . they will ohm out ok .dont mean to beat a dead horse. just think that a good total cleaning of all fuel lines and replacing the fuel strainer in the tank and another fuel pump may solve the problem

I wish I had my air compressor, to test the lines... but I will do what I can. I am going to remove the line and see how fuel is flowing.

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I spoke with my very good friend in Delaware, Travis. He is a wealth of info about diags.

He feels the EGR is stuck open

HE suggests removing it and replacing the valve with a bit of beer/soda can and covering the EGR hole. if it starts to run right, then the problem has been found.

I will test this tomorrow.

A tell tale sign is when the intake gets too hot to touch. Way too much exhaust entering and one massive vacuum leak!!

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That's a brilliant freakin' idea. Seriously. I wonder if that trick might help me to figure out my rough idle. I'm not getting any spark knock, but just a poor quality idle, and the car seems just a bit down on power in the mid-to-upper RPM range. Hot and cold. Standing next to the car with the door open and with your hand on the window, you can feel the whole car wobbling a bit at idle. I replaced my EGR solenoid and valve last year, but I've still been a bit suspect of it since then. Not sure why, just a gut feeling.

That's a pretty good testing idea, Andy. I'd still be looking at the ignition, though, too.

Matthew

Travis has been doing this for over 30 years... in one shape of form or another. And right now, he is an A-line tech at the local Dodge dealer... the man has been to more schools than I can count.

In short, I am starting with the EGR test... if that doesn't do it, then I will continue.

His logic is sound. If the valve "works", meaning it opens and closes as it should, it one thing. But if it has an internal leak in the valve... that you can't predict. And that leak is essentially an open exhaust leak AND vacuum leak. So the engine is fighting BOTH at the same time.

Think about the confusion of that... Think of what a vacuum leak does... and think of what an upstream air leak does to the O2 sensors... Combine the two... and it sounds exactly what I am dealing with.

If this is right, we will know in about 20 minutes.

I will be back.

Beer cans as a diagnostic tool - I really like that idea.

Well... beer cans don't work so well in our application.

On the engines Travis works works with, they do. You see, their EGR is more accessible. Ours, not so much. The idea is to slip the cut up can between the exhaust port and the EGR to block off the exhaust going in. Don't work so good when you can't reach.

I tried to make a block off plate with a can and that didn't work so good, either. You see, the exhaust coming in is greater than the vacuum holding, so it kinda ballooned and stopped blocking things.

Next was to put an EGR on that would serve my test... there are different part numbers for manual vs auto EGRs. My guess? The manual EGR has to deal with more exhaust surges caused by the manual shift, something an auto would not have to deal with. Hence, 2 part numbers.

I did put the EGR on from bastet's LT1 just to test startup and see if it gets all shitty at 180...

Got all the way to 190 and ran like a DREAM!!! No more spark knock, no more funky idle, no more backfiring.

Absolutely amazing.

As for the old EGR... I put a vacuum pump on it and it opened... but WOULD NOT CLOSE! It also took no pressure to open, so my guess is that the tension spring inside has died... Exhaust was forcing it open and the valve couldn't stop it. Also, the only way to close it was to whack it on the floor! It would go "TING!" and slam shut.

Let's all party!!! At least until THIS fix proves me wrong.



The new EGR is coming from NAPA and will be here Saturday morning. I won't need the car until then, so all is ok.

Way to go, congrats on a tough one!
I never came across a bad EGR, hence no experience with such a fault. This has been a nice learning experience, thanks for sharing your diagnostics.

Well done!!! Great thread for diagnosing knock problems, learned a lot.

Thanks! I think this has fixed it. It's the best empirical evidence I have learned.

The other thing I have learned is that a Code 32 isn't valve related but CIRCUIT related. I need to reread the Helm on it, but that's more and more what it looks like.

Interesting and I'm glad you found it. I'll have to check my FSM, but are there any tests for the valve itself while on the car?

Matthew

yea, a number requiring a vacuum pump.

way cool you have found it .sure glad my zr1s dont have an egr valve

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I think it's both, Andy.
While anything wrong in the circuit/vacuum can throw a 32, if the valve won't hold vacuum (bad diaphram), it will also throw the code.

I think you are right; that's why I need to check the book a bit closer.

This thread also proves the durability of the EGR valve. If we were scratching our collective heads over this, it makes me believe they simply don't fail; or are replaced before they do.

Not that it's particular to this thread but when mine went:

I got an SES lite, it turned itself off the next time I started the car, got a 32 too.

Nothing for a 150 miles, then the lite $ code.

Then the lite & code at fewer miles
100
50
30
10 - then I changed the valve.

The above is just the way it may happen.

Amazing. Good work Andy! Glad to hear she's running right again.

We will know for sure tomorrow when I get the new EGR.

Apparently, there is a different part number between manual and automatic EGRs.

My best guess is that the EGR for the manual has to be able to deal with the exhaust surges of a manual shift. That's my theory at least.

New EGR was installed on Saturday, and the car is running GREAT! I suspect the valve had been failing for some time now.

A great learning experience for all... and an annoying one for me.

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I'm guessing you got the old one out without having to lift the fuel rails. Man, that second bolt gave me fits when I did mine. What was your trick?

funny thing about our cars they can make you feel so darn good or they can make you madder than even your wives ever could . what a great hobby we have. who says god doesnt have a sense of humor

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strong, but rather thin, fingers... not longest fingers, just not super thick and meaty.

I was able to break them free with a wrench, and remove with finger force from there. Install reverse of removal.

It really helps to remove the EGR/AIR tube from behind the manifold. Gives a lot more space to wiggle it out.

Final Report:

The car is running great. Better than it has in months. If not years. I think that the minor exhaust leaks have been creeping up and effecting performance, however so minor.

The EGR has been causing me issues since the bad running problem in May. I also had a problem with an intermittent miss at highway speeds. If I was doing, say, 70 MPH in 6th, and gassed it, it would miss and then keep going. Pretty consistent... I think the EGR was failing then. Just a slow miserable death.