Hi there

Been fighting this for two weeks now. Started with check engine light coming on car ran rough, would not accelerate without serious missing thru rpm range. Checked all connections, tried to read pcm, could not communicate with my laptop. Removed power from battery for awhile, restarted seemed back to normal but still check engine light.
Replaced opti as I was going to to this anyway, car has 243k on it, and appeared to be original. Was going to do timing chain, but friend who was going to help and has a lift had to go out of town. So only opti for now. Anyway I have replaced all sensors except for knock sensor (I have multiples from various ex cars) same results. Car takes about 10 seconds to crank, I have to open throttle body for it to catch. Ran good but still check engine light till yesterday. Car starts now, idles well, but when accelerating it sounds like timing is off, car almost stutters when accelerating. Will coast fine, just sounds like it is running on half cylinders. Really would like to scan car, will try again today. So I feel it is either the timing chain or my pcm or both. I know the opti can only correct for timing variances of plus or minus 1 degree so if my chain had alot of slack, this may be my problem. With 243k on it, probably is stock, good idea to replace anyway. Friend is still out, just don't want to do this in my driveway. So Let me know what you think.

tia

andy schuck

 

The code would help, a lot.

 

+1 on the code. If there is enough slack in the chain it could have possibly jumped, but I can't ever recall anyone actually having it happen. Get the code for sure and double check your opti installation. Any idea on fuel pressure? With a car that has that many miles there are many possibilities.

 

Before the chain jumps, you would probably hear it, at least I did. I developed a tick that would go away about 2000 rpm that I (thought) was a lifter but narrowed it to the opti using a stethoscope. When I was replacing the opti, figured with almost 120000 miles and since I already had it all apart, I might as well replace the timing chain. Crikey, I have had bicycle chains that were tighter -- it had strecthed so far it was hitting the side of the cover at low rpm.

 

If I can connect to the computer that will be the first thing I will do. Will be doing this tonite. Will let you know what I find out.

tia

andy schuck

 

Skipping a tooth on a timing chain is a myth. At least in the last 10 years, I have never heard of anyone ACTUALLY proving their chain skipped a tooth.

 

The belts used on little motors make people think cam drives are a tuneup item. The LT1 chain is NOT a tuneup item, long as you are not putting a big cam and rpms to it a stock chain will last as long as the rest of the engine, and I have even used them with decent sized cams without an issue. It is a rock solid piece.

If you want to believe it is the timing chain you will have a hard time finding the actual problem.

 

Well after much hair pulling and banging of my head against the wall, I have figured out what the problem was. The main ground by the coil/icm was detached from the connector, so this side of the engine was not grounded. I believe this was the reason for no communication with my laptop. Once this was fixed, I found codes for the maf and coolant temp sensor, and the iat wiring was broke. The strange part was the coolant temp sensor wiring. It was just broke in two, inside the plastic wire loom. The maf had a loose wire at the connector. Freescan showed the iat and coolant temp were at -40, and with the maf wire loose, it was running rich, think I may have fouled a plug or two, will check those out. Car starts right up now Just goes to show that without diagnostic tools like a laptop, it is almost impossible to diagnose/repair modern fi cars. Thanks for all the inputs and help, I really appreciate it

later

andy schuck