First off, apologies if this is is the wrong section, but here is my issue-

My Trans Am that I bought a few weeks ago has a pretty significant miss off idle. Acts like it isn't getting spark to 1 or more cylinders, bucks and kicks pretty badly, especially around 1500 RPM. Doesn't really smooth out at higher RPM, just misses more frequently so it seems smoother.

From what the previous owner told me, it has a cam, and he put headers on, and deleted the AC and smog pumps. Tuned port intake.

Has spark at all 8 cylinders, plugs are gapped to .040. Timing is set to 12 degrees. All injectors are firing. This being said, I think the problem must lie in the sensors or the ecm. Tried the paperclip code reading trick, didn't get anywhere. Have no idea if the factory PROM is installed, don't know how to check.

Though it may be that I don't hear it miss, the engine seems pretty happy when revved quickly, and has decent power.

I am pretty much out of ideas, as I have never dealt with this amount of sensors and everything else the EFI needs.

Thanks in advance, Donavin

 

It could have badly mismatched cam to the rest of the combo. What kind of vacuum is the engine making at low speed? What's the fuel pressure? Is the timing advancing?

 

12* degrees? Try 6* and see if it helps.

 

I agree! Need to look at TPS and MAP sensors also. If the po changed the cam, a tune will need to be done if not done already. There seem to be a lot of sensors associated with EFI, but if you read and understand the tuning guide in the DIY PROM section, it will not be so daunting. Not knowing the cam specs and any other mods the po made, your basically starting from scratch as far as a tune goes. There are many brilliant members here on TGO, me not being one of them! You will need to learn how to data log and post those logs so others can see what your engine is doing. In order for others to help, you need to help yourself and learn as much about your car and the TPI system. Again, the tuning guide is a great start to helping you understand what affects what and how to compensate for changes made to the base system. Get reading and when you're ready, try some data logging. Post your logs and the experts will surely point you in the right direction. Good luck!

 

The way the car idles, I doubt the cam is very big at all. If I had to guess, it's a .430 lift, 212 duration. Would something that size screw with the computer that badly?

Not entirely sure how to check fuel pressure, don't have any kind of line like a carb does.

I'm debating whether or not to just throw a carb intake on and call it good.

 

Has a Schrader valve on the rear of the passenger side fuel rail for checking pressure.

 

Sounds like a start over and recheck all the previous work.

 

The tps sensor could be bad, not reading right at lower throttle opening angles.