MikeC4

Hey everyone, I've been away for awhile, been busy moving and all the fun that comes with it!!

Well, my '95 is acting up again. Just yesterday, I noticed that at idle, both in open and closed loop, the RPMs have dropped somewhat and I can feel engine vibration through the steering wheel. The engine feels as though it is going to stop due to bogging down, but it does stay running at idle. When I go WOT, the car accelerates like a Camary running on 2 cylinders. This problem appeared overnight. I checked for codes with paper clip, and no codes thrown. I checked the fuel pressure and fuel pressure bleed down, no problems here. Car has 69.5K miles. I checked all around for vacuum leaks, and nothing seemed to be sucking air. While idleing, I popped of all 8 FI plugs one at a time, and the RPM's drooped on every one. I also disconnected the MAF plug while idleing and the engine did quit, so I assume it is OK.

Within the last 6 months or so I replaced the Opti, WP, TPS, plugs (Bosch Platinums), IAC and both O2 sensors. The engine has been running great up until yesterday....

Any ideas on what could cause the engine to run fine one day, and the next dayrun like a POS ????

Thanx folks...and it is great to be back!!!!

96GS#007

Sparkplug wires and/or coil wire need to be checked.

Lone Ranger

Sort of sounds like fuel starvation. But you checked for that. Hmm...

Check ignition coil and Ignition Control Module. Actually I don't beleive ICM's can be tested, though.

I do know that a failing coil can take an ICM down with it. Happened to OneDef92's car.

MikeC4

thanx Lone Ranger, I also forgot to list that I replaced the fuel filter and Coil within the last 6 months or so. Fuel starvation was my first guess too. At idle, the FP gauge reads ~40psi. When I throttle it hard, the gauge only drops down momentarily to around 37psi, and returns very quickly. But since I observed a steady 40psi at idle and the engine still idles low and rough, I concluded that the fuel deilivery system was OK.

And I replaced the coil in February, but that is not to say that it could not fail prematurely. I will stick in my old coil today and see if I notice any change in engine operation.

Now the ICM - i suspect that this is original. I had one of these go bad years ago on a '78 Camaro Z28, and when it went bad the engine just died completely. Can an ICM which is going bad exhibit the kind of "2 cylinder Camry" power which I am experiencing before dying completely?? That was 15 years ago, and my only experience with an ICM going bad...

Thanx!

redbullapril23

have you checked the plugs?
pull them and see if there is a bunch of gunk and black junk on them
suggesting that that cylinder isnt firing.
that way you can narrow it down to either the plugs, opti etc..
just a thought
your friend
Sean

Lone Ranger

I've also heard cases of the coil wire coming loose, so check the connection at both ends.

ICM symptoms I'm going to let someone else chime in. My knowledge is that they can die slowly (car runs badly) or fail outright (no start condition).

MikeC4

I put in a new ICM made by Borg Warner and the problem is still there.
I put in an old coil I had lying around and the problem still the same.

What I did notice is that for the first couple of minutes, the engine was cold, the car ran and accelerated fine before it started to bog down as before. The poor performance starts way before the engine goes into closed loop operation.

I am now thinking clogged catalyst(s)??? What do you think?? Are symptoms of clogged cats a sluggish and very poor accelerating engine?

I am going to pop off the O2 sensors to relieve excessive back pressure to see if that makes any difference.

Lone Ranger

In summer temps, the engine goes into closed loop around 90F coolant temp, so it still could be a closed loop issue.

Yes, but I don't see it happening overnight like this has.

I don't think this (removing O2's) will help.


Map sensor:
Even though MAP sensor is a key component in Speed Density cars it is still important in MAF cars for spark timing. Have the MAP sensor tested. They are testable.


Make sure the EGR valve is not stuck open, or sticking open after the first call for EGR by the PCM. The EGR valve can be cleaned pretty easily. Just have to remove it and a have a can of throttle body cleaner handy. Use only Throttle Body cleaner, it leaves no residue. Don't spray any kind of lube or dry lube (silicone) at it, just use throttle body cleaner and keep spraying and letting it run off until it's clean. Don't forget to spray and clean up the inside of the EGR port on the intake while you have the valve off, but this can be hard to do. I took a small strongly woven rag (no fuzz or threads coming off), wrapped it around end of short screw driver, sprayed it soaking with throttle body cleaner, and used it to clean out the EGR port on the intake as best I could-- clearance is tight back there, hard to get to. The surface of the EGR port that mates up to the end of the pintle in the EGR Valve is the main part of the port to try and get clean, and the end of the pintle on the EGR Valve you want to get as clean as possible also-- these are not the block-off sealing part of the valve that stops the flow of exhust gas, but if they both get enough build-up the buildup can possibly keep the gas port on the valve neck from closing all the way.

resipsa

I have a 95 with 54K on it. It has the usual LT1 oil leaks which means that the right side O2 sensor connector (at least on mine) gets exposed to oil. Because ambient air is drawn into the sensor by way of the connector in normal operation of the sensor, oil drawn into the sensor from the connector will destroy the sensor. My original sensor lasted 26K. The second one (OEM) took me to 53K. The third sensor (a bosch POS) took me 1K (last than one year). I just ordered a pair of Denso O2s which are supposed to be resistant to oil and more robust.

MikeC4

Thanks Guys....
resipsa - what kind'of name is that? ..excellent point. I did my intake manifold about a year ago and just recently chaaged out a leaking oil pressure switch, so at this point in time, I have no oil leaks to thrash my O2 sensors.......give it time... DOH

Lone Ranger-

Good call on the EGR valve, it was absolutely packed with chunks of carbon. I just went ahead an replaced it....

You got me thinking as to what was the cause of my clogged cats. I haven't had them replaced yet, and I am hopeing to get to the root cause. I don't want to risk ruining a new set of Cats. In that I care about the environment, I am not going to gut my cats or run without them...I want to check my injectors thoroughly for leakage, and as you suggested, check my MAP sensor....

Do you know what the typical life expectancy is for a cat? My car is 10yrs old with almost 70K miles. These catalysts have to filter a world of crap, especially during the times when the engine is not running at peak performance.....


Rgds,
Mike

aboatguy

My 95 has approximately the same milage and the cats are fine.
I doubt that the cats would clog quickly so if this is a new problem, I would start elsewhere.(IE O2 sensors?)
Have you conducted a scan while its running to see whats going on? These cars will tell you so much if you have a data logging program.
Mike

MikeC4

YIKES......................
well, after putting in new EGR valve, cleaning off lots of black carbon from the O2 sensor outer casing, the engine runs better but after about 5 minutes of driving the idle stumbles, then the SES goes on, idle then gets better, SES then goes out, idle stumbles...ad infinitum.

(I did disconnect the neg. Bat. terminal to clear history codes after disconnecting each injector, MAF sensor, MAP sensor, O2's, etc. over the weekend while the engine was idleing..)

Dumped the history error codes and now get these:
H48-Mass Air Flow (MAF) Sensor Circuit
H44-Bank 1 (Left) Heated Oxygen Sensor (HO2S) Circuit (Lean Exhaust Indicated)
H64-Bank 2 (Right) Heated Oxygen Sensor (HO2S) Circuit (Lean Exhaust Indicated)
H18-Injector Circuit(s)
H34-Manifold Absolute Pressure (MAP) Sensor Circuit ( Voltage Low - High Vacuum)

I am at a loss as to what to do next. I am concerned about the injector code...?? I think I do need to scan / datalog the engine, but I don't have this capability yet.

I hate it when my Vette is sick!!!

resipsa

MikeC4,

My screen name "resipsa" comes from the latin phrase "res ipsa loquitur" which means "the thing speaks for itself". The term is used mostly in law. Last time I heard, U.S. Supreme Court Justice Clarence Thomas had "resipsa" on the license plate of his ZR1 Corvette. I thought it was cool, so I started using it as my screen name.

Lone Ranger

I don't think the codes set by your disconnecting the various sensors during attempt to diagnose, got cleared. They seem to match the things you disconnected.

I am at a loss. I think you need to have the car scanned and some data captured by the scan to see what's up.

One last thing: Are the plug wires original? In the past I've had a wire arc on me, #1 cylinder arcing from plug boot to the exhaust manifold. It wouldn't do it until the engine got warmed up, and even though it was only one cylinder misfiring the car bucked badly and felt like it was going to stall, plus felt very sluggish.

When its doing this thing you describe, pop the hood in the dark and listen for the snap-snap-snap sound of a wire arcing when its running poorly, and look along the length of each wire to check for arcing.

MikeC4

ARGHHH...

Had new cats installed, but the problem still exists. My current problem is what probably killed my old cats, which you could hardly see through. I suspect that if I continue to drive the car as is, I will kill these cats in short order......DOH

Lone Ranger, you were right, I probably didn't clear my error codes correctly before. I cleared them again, checked that no errors came up before starting the engine. All codes were cleared.

Todays excersise:
-Engine still running real rough after a minute or so of driving
-SES lights up and idle smooths out somewhat
-SES eventually goes out and poor idle is back, stumbles and shakes abit
- H64 error code stored
-continuous plume of black smoke coming from right exhaust at idle
-small amount of black smoke from left exhaust, but hardly noticable
-pulled one plug on passenger bank, covered with black particulates(1 year old plugs with about 7K miles on them, Bosch)
-checked all 8 FI resistance. All between 13.2 - 13.4 ohms
-cursed at vette about 20 times. Feeling betrayed. Want to embed a 357 in the block, but this may excite the neighbors....

Plug wires are original, and I will check for arching this evening.

Lone Ranger

Check wiring path for each oxygen sensor. The H64 code in combination with the black smoke coming out mainly on right pipe is a red flag for that oxygen sensor. It may be that the wire has a short in it somewhere between the sensor and the PCM. I hope not. That can be a bear to track down.

Better to spend money on a professional scan and diagnosis than go around feeling bad about your car.

MikeC4

Thanks LR, and one other piece of info. I forgot to note is that my AVG. gas mileage has dropped from about 16MPG to about 9MPG. (I know it takes time to get accurate AVG since I reset it when I cleared my codes, but I also can see that my instantaneous MPG is below 10mpg, even when cruising at 40-50mph, with no acceleration)...

BTW, I still love this car....just getting frustrated with the complexity of the later year Vettes. Prior to the '95, I have owned nothing but C3's, which were so much easier to diagnose without the aid of computers and such.....

Atok

Check your MAP sensor.

Lone Ranger

If you've got a laptop PC, you might want to consider buying an interface cable from AKMCables so you can connect your laptop to your Vette's ALDL socket (Assembly Line Diagnostic Link, otherwise known as the socket that scanners connect to). Then download a FREE copy of TTS Datamaster, and also download the Datamaster PCM image file for 1995 LT1 (DM32xEE.exe). Install it on your laptop and then you can make a scan of the car yourself, Datamaster will record engine or automatic transmission data while you drive, and save it as a file you can playback later and analyze. Or maybe someone could analyze the file for you.

Your mpg indicates a pig-rich condition. I would not drive it so much until repaired since you just hung new cats on it you don't want to clog them up right away.

If you don't have a laptop, then post a message paging forum members in your area and asking for name of a fair, competent, and trustworthy shop in your area that other forum members have had good luck with and take the car there for diagnosis.

kingcato

that just happened on my 95 A4, took it back to the shop, turned out that when i had gotten one of my o2 sensors replaced a month back, that it was worse than the original, got that one replaced and now it runs a ok