Help! Car running rich

[purplec4]

I have a 95 LT1, if I disconnect the battery for a while then reconnect it the car runs fine for about 25 miles. It then starts to run rich and rough, loss of power etc, I had a spare engine control module which I swapped and the results were the same. I don't know what resets or what happens when the battery is disconnected but it always runs good for about 25 miles when reconnected, then the same. Thank you for any ideas, hints, tips, thoughts etc!

 

[Hib Halverson]

I have a 95 LT1, if I disconnect the battery for a while then reconnect it the car runs fine for about 25 miles. It then starts to run rich and rough, loss of power etc, I had a spare engine control module which I swapped and the results were the same. I don't know what resets or what happens when the battery is disconnected but it always runs good for about 25 miles when reconnected, then the same. Thank you for any ideas, hints, tips, thoughts etc!

Is the Check Engine light on?
Do you have the Factory Service Manual
Do you have a scan tester?

Tell us what recent maintenance you've done.

 

[Otter]

I have a 95 LT1, if I disconnect the battery for a while then reconnect it the car runs fine for about 25 miles. It then starts to run rich and rough, loss of power etc, I had a spare engine control module which I swapped and the results were the same. I don't know what resets or what happens when the battery is disconnected but it always runs good for about 25 miles when reconnected, then the same. Thank you for any ideas, hints, tips, thoughts etc!

Had the same problem where on initial start, car would run great for 15,20 minutes, then lose power and I would have to limp home. Turned out it was 2 bad injectors, replaced all injectors and all has been well for 2 years. Not sure if that would be your problem, but with a multi-meter, its quick and easy to check your injectors.

 

[purplec4]

Running rich

Is the Check Engine light on?
Do you have the Factory Service Manual
Do you have a scan tester?

Tell us what recent maintenance you've done.

no check engine light, I have to factory manual, no scam tester, within the past 20,000 miles plugs, wires, one cat converter, vacuum tee, fuel filter

 

[Hib Halverson]

no check engine light, I have to factory manual, no scam tester, within the past 20,000 miles plugs, wires, one cat converter, vacuum tee, fuel filter

There were some typos above...do you have a Factory Service Manual?
Also, do you have a fuel pressure gage and a DMM?

Does the Check Engine light come on at bulb check?

 

[purplec4]

running rich

I do have a factory manual, no DMM, the check engine light came on once for about 20 miles then went off and never came on again, it works, also I forgot to tell you when this first happened I smelled an odor like hot exhaust when I parked the car, the car did not run hot and the odor has not happened again, the check engine light does come on at bulb check and goes out once the car is started. THANK YOU for your efforts, it is much appreciated.

 

[WhalePirot]

Disconnecting the battery will erase any ECM codes which seem to be real and recurring. I know the earlier shortcut to pull codes, but not those on the '95. Many 'chain' auto parts stores will 'pull' codes for no charge.

I wonder if that aroma was CAT sourced. Doesn't the '95 have 4 O2 sensors?

Upon initial startup, before the car is warmed up, the ECM is in open loop where most sensor inputs are not part of its computations. Those ECM codes are essential for troubleshooting IF the basics (proper vacuum, fuel pressure, electrical connections, etc.) are good.

 

[Hib Halverson]

Ok...
no scan tester
no fuel pressure gage
no DMM

The manual you have...is it the two-volume factory service manual or one of the aftermarket shop manuals from Chilton or Haynes?

How did you decide the engine was running rich?

Air filter been changed lately?

 

[purplec4]

Ok...
no scan tester
no fuel pressure gage
no DMM

The manual you have...is it the two-volume factory service manual or one of the aftermarket shop manuals from Chilton or Haynes?

How did you decide the engine was running rich?

Air filter been changed lately?

Thanks for the help guys, I have the 2 volume factory service manuals, I also now have a DMM, air filter is almost new, I am going to take the car to Auto Zone to have them scan it. The car now runs horrible for about 5 to 8 miles then the service engine soon light comes on and the car runs good until I shut it off, if I restart it the service light will stay off and it will run bad again for the 5 to 8 miles until the service light comes on again. My fuel mileage fell off about 7 miles per gallon, my exhaust has black soot on the pipes, if I rev it up I can see black smoke in my mirror, WhalePirot I am not sure how many sensors it has and the smell is not any cat smell I have experienced in the past, the soot is on both sides of the exhaust.

 

[ecss]

I am going to take the car to Auto Zone to have them scan it.

With a paper clip or piece of wire short Pin 4 or 5 which are both ground to Pin 12 on
the diagnostic connector located above the drivers right knee.

Turn the ignition switch to On. Don't start the car. Look at the speedometer LCD.
Codes will cycle and display on the LCD.

Module 1 is the CCM
Module 4 is the PCM

 

[Rob Dennis]

Still have the issue?

Hey Purple - Are you still having the issue? I too have a '95, and can walk you through what to check.

Anyhow, without any diagnosis at all, I'd check for a stuck EGR valve. Just articulate it with your hand and see if it moves freely. With the engine idling, opening the valve should make the idle worse, and then it should get smoother after you let it go. It's at the back of the intake, where the distributor used to be (before OptiSpark). Be careful, it can get hot, wear a gardening glove. Don't use a sharp tool to articulate it, you don't want to puncture the rubber vacuum diaphram. If it stickes open (or closed) then take it off, hold the diaphram open with your hand and carefully clean the carbon build up out. Compressed air works great for this. Make sure you don't gouge the valve seat with anything sharp. To test it, apply vacuum with a hand pump and make sure it opens and that it fully closes once the idle bleeds off. You can usually re-use the gasket if it doesn't rip when you remove it - but use your judgement - the gasket is cheap. Put 'er back on and see if it's fixed.

My other suspicion is a bad O2 or another sensor, but sensors in general aren't chaep, so you want to diagnose that before you start buying things. WhalePirot is right, until the engine goes into closed loop (which happens when it reaches normal operating temperature) it uses reference values programed into the computer. Which leads me to believe this is a sensor issue. Sensor issues are much easier to diagnose if you pull the codes from the onboard computers. The proceedure ecss references is spot on correct to get the codes. Since you have the FSM, you can read the full proceedure there. It tells you how to do it in the second volume. Section 8 shows you how to pull codes, as I recall. I can look in mine and tell you the exact page number if that would help, just not at the house at the moment.

There are four "computers" in my '95, a CCM (module 1), the PCM (module 4), and two more I can't remember this second (they are module 9 and A, I think ABS and ASR). Anyhow, write down any codes that you get and share 'em here. Note that code C12 from module 1 means a clean test of the CCM (so, it's normal to see C12, we don't need this one).

Hope this helps!

 

[purplec4]

Thanks for all the help guys, I have been out of action lately but am back now so here goes. I appreciate all your help and will be able to work on the car tomorrow. The car just does different things all the time, runs super rich sometimes, when I stop at a light sometimes it will stall as soon as I give a little throttle to take off, when it stalls it takes about 30 seconds of cranking to restart, service engine soon light will come on after about 5 to 7 miles driving and when it does the car runs better, my fuel mileage is about 12 to 14 miles per gallon when running real bad, 18 to 20 when running kind of bad. I used to average about 25 per gallon. I had the battery disconnected for a while when I replaced the fuel pump recently, when I drove the car after installing the pump and it really ran bad for about 75 miles, now it runs fair and it seems to be running about the same the last three times I took it to work. Will start up and not run very good for that 5 to 7 miles then the engine light comes and my fuel mileage increases and it runs better. If I shut it off the service engine light will again stay off for the 5 to 7 miles. I know this sounds like it's all over the place but that's what the car is doing. Something else I just thought of, when the car is running real bad and is trying to stall the word LO appears on the display where the temperature numbers usually are. I will work on it tomorrow and keep you up to date. Thanks to you all for your help, it is appreciated.

 

[Hib Halverson]

What fault codes are set in the ECM?

If the digital display says "Lo" even after the engine has been running a while, check the ECT sensor and it's wiring.

 

[purplec4]

Hey guys, I did the paperclip trick and got 3 codes, C12, H44, and H15. I think the C12 code is normal, the H15 code would explain my coolant temp reading LO on the display sometimes and the H44 is a left side oxygen sensor reading a lean condition which would explain why the car runs so rich. My next question is, is the left side the driver's side? I think it is but not 100% sure. When they say left does it mean sitting in the car? I'm going to jack up the car now to see if the o2 sensor screws into the exhaust or what the deal is. I hope this is something I can do myself. THANK YOU guys for all your help and advice it is greatly appreciated and I will let you know my progress.

 

[purplec4]

Well today was the day I changed the 02 sensor, borrowed the tool from Auto Zone and it was not as difficult as I figured it would be. When I removed it I found it totally loaded with carbon, the slots on the side were blocked with carbon. Took it for a ride on the highway with the A/C on, yes it's still hot in Florida, and got an average of 26 miles per gallon up from the 17 I got yesterday when the task was done. THANK YOU all for your help and while not wishing any problems on you I hope to be able to help you some day also! Thank you!

 

[WhalePirot]

I'd want to be sure that whatever carbon fouled the oxy sensor, won't foul the new one. ECT is the engine coolant temperature sensor and if the ECM 'sees' a colder engine from a faulty or failing ECT, it'll squirt more fuel that a warm engine needs. Additionally, any fouling of the new sensor may be your good news, as a rich or oil burning engine will foul the cat(s).
A vacuum leak can also 'fool' the ECM with unmetered air entering, causing a lean condition, that the ECM will attempt to remedy. Watch closely for the symptoms seen earlier, especially the LO indication.

 

[purplec4]

Thanks for the advice, will do. I bought a new sensor on the way home from work yesterday and will install it today when the engine is cool, I never thought of it until you explained it but sometimes my digital temperature readout would also drop from about 200 to 172 or so occasionally when driving. The sensor cost $21.00 so I think it's probably a good thing to change anyway. I have had the car for 8 years and plan to keep it the rest of my life. Thanks again, your car in the picture is beautiful.

 

[WhalePirot]

car in the picture is beautiful.

Thanks. I hope there's no more trouble with your fine ride.