I got this 93 Trans Am and it is runnin like crap. No power. heats up to 240F. Pings like a **** and backfires so I am sure it is a timing problem.
On the scanner, it shows 17 degrees SPARK AdV. at idle and at acceleration it falls to 0-10 degrees.

Now my questions are:::::::
Isnt the timing supposed to rise to 40? at accel and then slowly decline back to around 20 when cruising?

Is the SPARK ADV. pid on the scanner the ACTUAL timing on the engine or is it the timing that the PCM WANTS the engine to have??????????


The SPARK ADV does not ever pass 25 degrees while driving and has even hit negavite -10 degrees while cruising. It generally stays in the 0-10 degrees area. This is a 93 and I THINK these cars came with the chip in the PCM and I am thinking that the chip is to fault. any other suggestions would be appreciated. thanx


JD

 

shoebox, injuneer?????????


anyone


my thread is floating awayyyyyyyyyyyyyy

 

What does your scanner indicate for "knock retard"? That's what you need to be looking at if it "pings like a ****".... if you can hear knock (which is different than "ping", but I suspect you mean "knock"). You should NEVER hear knock in a healthy engine. The ECM can pull up to 15deg timing to reduce knock to the inaudible level.... if you are still hearing it, you have a huge problem.

I've never looked at a 93 program, so I don't know if the spark tables are the same as the later models. The "advance" you read off the ECM is the value that the ECM hac calculated, using the timing table (deg advance vs. MAP/RPM), "+" any offsets from the IAT table "-" any spark retard. To get the total advance the ECM is calculating from the program table, if it had no knock retard, you need to add the "advance" number and the "knock retard number". In general, this will be the number programmed into the tables of advance vs. MAP/RPM, except for an occasional elusive 3deg extra advance that may come from the IAT offset (I've never seen anyone confirm the source, only that the 3deg does often appear).

In a 94+ the idle advance is 18-20 degrees. Some scanners will show advance as a "+", some scanners will show it as a "-". In any case, at idle, 17deg sounds normal. When you go to WOT (MAP = 95-100) advance will increase with RPM, ranging from 9deg at 1,000rpm to 33deg at 4000rpm (and higher at higher RPM... I just don't happen to have the high RPM table in front of me.) I'd say you can see 38-39deg at WOT/max RPM.

When you back off completely on the throttle, the ECM will back off on timing... you might see 10deg. When you are cruising at low throttle, moderate RPM, you will see as much as 45deg advance.

 

I already checked the knock sensor and it isnt doing anything. Its not indicating knock and not trying to subtract timing.

 

this pinging noise........I only get it when the engine is under heavy load........like going up a hill or WOT acceleration. even accelrating off a stop, it will ping a bit.

there is no noise when there is no load or in nuetral. you can rev it up and wont hear a thing. it sounds good at idle but the rpm does swing up and down 700-900 uncontrollably.

also.......why would the scanner be showing 15+ idle then at accel drop and go the other direction. It will fall to 5+ degrees then 0 degrees -5 then -10 degrees. does not go further than -10 degrees. at 0 - -10, the engine runs horrible and will barely accel the car.

If the timing is all inside the ECM.......then wouldnt this automatically mean the ECM or ECM prom is screwed?

 

Have you checked the knock sensor wiring to make sure someone hasn't "desensitized" it? That's a popular mod for the 93's. If it pings or knocks, it should trigger the knock snesor circuit. You need to sort that out.

But with all the other problems... backfires, pinging, rough running.... it almost points to ignition timing problems, and the Opti could be the source, including dirty contacts on the harness connector, or even a high voltage ignition wire runnin too close and in parallel with the Opti harness.

 

Is the MAP sensor used to calculate timing?

Lets say the MAP sensor is faulty.......would this cause major retarding by the computer?

I looked into your timing chart and saw that the rpm and the kpa calculate advance. correct me if I'm wrong, but isnt the MAP sensor also the kpa sensor?