What I have here is a problem that i can not find and 2 dealerships in southern ohio can not find. Computer is not storing any codes and only thing that has been diagnosed is the car is retarding the timing from off idle to 2000rpm all sensors are reading within specified values , fuel pressure is fine , new optispark,plugs,wires,map,knock sensor there are know signs of sensors pulling timing ,temp sensor is ok. last dealership I had thought the timing chain was off a tooth but would not guarntee this , I would think if this was the problem it would pull timing through out rpm range not only to 2000rpm
Symptoms are bad hesitation, running a littlewarm around 230 degrees , very bad gas milage and around 5000rpm timing is going ape crap, I f any won has a few suggestion I would greatly appreciate it ,getting tired of paying gm dealerships to not fix my car Thnaks so much

 

Does it have knock retard? Has any work been done to it,ie. cam,timing chain,etc.?

 

No work has been done to it she is bone stock, scanner shows know knock count this is according to the tech 2 scanner

 

Either the chain has jumped or ya got knock retard when ya shouldn't have.
There is a possibility it is the computer but not likely. The dealer should have checked it anyway.

 

Give some details on what the "retarded timing" actually is. The information is ambiguous at best. You say there is retarded timing, then say there are "know" signs of sensors pulling timing. Which is it? Do you just mean that it runs like it's retarded.

 

I'm glad you asked that question Shoebox.... I had a hard time understanding how he knows its retarding the timing, but has no signs of pulling timing.

The fact that the Tech-2 doesn't show the knock count increasing means nothing, because its possible to get knock retard without the count incrementing.

shaley1975 - Also would help if you added a "signature" with basic data about your car... year, model, tranny, any major mods. Since you indicate you have a new Opti, is it possible you have a 93 or a 94 with the splined Opti drive shaft, and the shaft is mis-aligned by one tooth?

 

The A/C clutch bearing on my car started making noise and I had a noticeable loss in power and gas mileage. I assumed the noise was being seen as knock and the timing retarded. Once the bearing was repaired power and mileage returned to normal.

If you have any rough bearings in the accessories or other metal to metal noise it can cause the timing to be retarded.

 

What kind of noise did it make?

 

I don't know how to describe the noise. Just kind of a grinding noise. It was audible inside the car. It was easy to tell what it was on the A/C since it only made noise when the clutch was disengaged. When the clutch engaged and the bearing stopped spinning the noise stopped. It might be harder to tell on the alternator or power steering pump.

 

The timing is actually being retarded between idle and 2000rpm the sensors are all reading fine via gm dealership, swapped pcm no difference, why is engine pulling timing?

 

This may help matters it is a 94 t/a lt1 , 4l60e trans

 

You still haven't answered the questions.... you just repeated what you already said.

HOW do you know its retarding timing? How much knock retard is shown on the scanner? Under what conditions does it retard timing between idle and 2,000rpm - ALL the time, under light load, under heavy load, at WOT, all of the above?

What exactly happens when you exceed 2,000rpm? Does all knock retard suddenly disappear?

What exactly happens at 5,000rpm when "timing is going ape crap"? How do you know the timing is "going ape crap"? Since you've said there's no knock retard above 2,000rpm, what IS happening to the timing?

What sensors are "reading fine"? Are you including the knock sensor in that staement. Knock retard can be caused by three things..... true knock, picked up by the knock sensor. False knock - often extraneous engine noise - picked up by the knock sensor. Faulty knock sensor, causing the PCM to use various engine operating parameters to calculate a variable and almost full-tmie knock retard. It doesn't sound like the last one, because you would have DTC 43 if the knock sensor or wiring is faulty.

Do you have any engine noise that could be mistaken for knock.... roller rockers? .... banging exhaust? .....loose motor mounts?

Is it possible there is a high voltage wire running near and in parallel with the knock sensor harness wire?

Did you consider the suggestion that the Opti may have been installed one tooth "off" on the splined drive shaft?

If you can't answer the questions, or clarify your post, its going to be very hard to help you.

 

From off idle to 2000rpm car is complete turd at wot ,mechanic said there was no knock showing on scanner, but the timing is showing up retarded on the engine scanner .After 2000rpm the car picks up and drives as should until it reaches 5000rpm and then missing and backfireing acures, mechanic says timing is jumpimg all across the board at 5000rpm

Opti was checked for misalighnment and was ok

Has no motor noise, or loose exhaust , motor is tight , has great compression just has that damn hesitation

As for the sensors he said all sensors were ok and I suppose the knock sensor is ok it is new

And what about the high voltage wire running by the knock sensor harness I havent checked this what could this possibly do.

I appreciate any help you can give me If I havent clarified enough please let me know thanks

 

Still need to know exactly what the timing values are. Just saying "the mechanic says" is not enough to tell anything. Details are what are needed. I know you probably don't have the tools needed, but in a case like this, a datalog would be the most helpful way for someone to "look" at your problem. It does not seem to be in the more ordinary realm of problems.

A plug wire near the knock sensor wire might possibly influence the knock sensor circuit readings.

 

That's where it gets confusing. There are only two things the mechanic can look at on a scanner.... 1) ignition advance.... and 2) knock retard.

When you look at the ignition advance with a scanner, all you see is the value for spark advance that the PCM has looked up in the table programmed into the car (with a possible 3* offset for IAT, but lets not complicate things). All you see is the advance the PCM wants to use. There is no way to see the actual timing of the ignition. Even if the Opti was installed incorrectly, it will not show on a scan, because the PCM has no way to know the Opti was not indexed correctly to the cam. It will still be calling for say 30* advance, but if the Opti is off by one tooth, the actual timing will not be 30* advanced. And there's no way to see that.

Is it possible your mechanic is seeing timing values of "-25*" (for example), and assuming that means the timing is retarded 25*? Because that's not what the minus sign means when it shows up on a scanner. It just means the timing is ADVANCED 25* relative to TDC. Not all scanners show the "minus" signs, because is does confuse some people.