I have a 1989 C4 that I bought about 3 months ago (iowa winter) and have been working on it in my garage. I've driven it about 100 miles on and off in between repairs and its ran great. However, the other night I get in and while backing out of the drive it surges and the Service Engine Soon light comes on, the Instant Fuel Rate quits working and the One to Four shows up on the dash. It went from idling around 600 to 1200 and ran a little rough. The next day I took it on the highway and after about 5 minutes it surged again and all 3 went away and started to run great again and ran great the rest of the trip home. Today I get in it and start it up and there are all 3 again. This time after about 15 minutes of driving/running the idle goes down to 600 while running rough but the One to Four goes off and the Instant Fuel Rate starts to work again but the Service Engine Soon light stays on and is still running rough. Here is what I've done mechanically since I bought it: new rotors, pads, shocks, tires, plugs, distributor pack, plugs, oil change, trans fluid/filter change, air filter, tensioner, serpentine belt, intake gasket. I cleaned the MAF sensor.
All of this has happened in the beginning, middle and end of all of these repairs so I don't think it's anything that I've done BUT...
I also hooked my code reader up but it won't read the car.
I NEED HELP PLEASE!

 

Try this for reading the code(s).

 

STOP-- please throw no more parts at your car until you read your codes. You car is designed to tell you hat is wrong. You need to get in the OBD1 system and read the codes. Use a paperclip- it does work.

There are dozens of DIY code reading tutorials on YouTube. Grab a beer and watch them for 10 minutes and report back.

FWIW... I bet you have an O2 issue.

 

A few years ago my '88 was acting crazy, like yours seems to be. I replaced the ECM [electric control module], and it solved the problem.

 

I tried to check the codes with the paper clip trick in A & B and it blinked the 12 twice but never went further.
I replaced the O2 sensor since it was cheap. It does seem to run better but when I removed the negative battery cable for 15 minutes the SES light was still one.
I'm wondering if the Lucas gas treatment I used in the 1st tank and the SeaFoam in the current 2nd tank loosened up some carbon and the EGR valve is plugged. I unplugged the vacuum line from the EGR and it started then ran without dying so I plugged the vacuum line back into it and it kept running. I ran it on the highway for about 20 miles and it ran great but still worried about the problem coming back and how I will get the SES light to go out.
Where is the ECM located?

 

I'm confused on how the engine is running? The way I read things, the engine is running much better but you have a SES code.

I'm also confused on when you got the code and when you tried to erase it? before or after you swapped the O2. BTW.. TOO MUCH engine treatment will mess up the O2 sensor temporarily.

 

It was running better yesterday, I think it still needs some attention though. I'm going to check timing.
I still have the SES light on. I removed the negative battery cable to erase the stored codes (like I read) after it started running better (after I replaced the O2 sensor) but when I started it back up the light was still on. When I tried the paper clip to read the codes it didn't work for me again.

The old O2 sensor was REALLY BLACK BAD. I think when I used the Lucas on the 1st tank of gas and started the SeaFoam on the 2nd tank I really loosened up some carbon build up and caused the issue myself. Now I'm wondering if I caused a clog in the EGR valve. I'm wondering if the EGR will slowly clean up on it's own as I burn the SeaFoam in this tank. ???

SIDE NOTE: will taking off my Catalytic Conv do anything negative to my car? I have to have the exhaust fixed and thought about just removing it since I might have caused all of this carbon build up to move around.

 

Hey Iowan from another Iowan! PM me, where you from?


The code problem indicates the ECM is down. Do you happen to have a field service manual (FSM) for your '89? I'd walk through the ECM diagnosis.

I had similar code problems with my '87 and had to replace the ECM.

From my '87 FSM:

Functional Check
~
I. Turn ignition ~~ON".
2. Enter diagnostics. <--- this is the paperclip
A. Code 12 should flash four times (If no other
codes are present). This indicates the Mem-
Cal is installed properly and the ECM is
functioning.
B. If trouble Code 51 occurs, or if the ~~Service
Engine Soon" light is ~~ON" constantly with no
codes, the Mem-Cal is not fully seated or is
defective.
• If not fully seated, press firmly on the ends
of the Mem-Cal.
• If it is necessary to remove the Mem-Cal,
follow the previous removal instructions


Hmm, re-reading that, since the SES is staying on, could be your mem-cal has gone bad. But like it says, try reseating it 3 or 4 times.

 

With your problems combined with the dash electrical it's probably time to make sure the dash and everthing else is grounded. Use a multimeter. It's so easy to do and a bad overall ground affects so many things and if it's intermittent even harder to identify.

 

If you plan to keep the car for any length of time, I would suggest a scanner instead of a code reader, which is a glorified paper clip and in this case, not working for you.

Well, it has been having exhaust hit it so it should be a little dark but over the years, who knows. It gets slower and slower and slower till it goes far enough to trip a code. The system isn't that sophisticated and only notifies you when something goes far out.

Keep dreaming. You are reciting the ads about carbon, etc, etc. For the price of a few dollars it will clean out your fuel system, engine, exhaust, and even whiten your teeth. Forget the snake oils. If they could do anything, mechanics would be out of business or at least severely curtailed.

Define negative? For one, I will not remove it if I am a shop. It can get me heavily fined. Another issue is it will make more noise. Yet another is it will probably not pass inspection. So before you get into the carbon removal dance, why are you removing it? If it is old and you want to get something newer and more efficient, sure.