Have a 1992 f150 with a 5.0 302, has mass airflow conversion and later model cam so it has a different firing order. I've eliminated vacuum leaks with a smoke machine and unplugged each cyl while running to see if there's a difference or not.

Has good spark on all 8, has compression at 130 on all cylinders. Unplugging maf and using the old computer with maf unplugged made no difference. Maf conversion told me to vent map sensor to atmospheric pressure and I've hooked it up and even hooked an air gun into it with no difference. I've replaced the egr valve because it had a code and it still surges from 500-1500 or higher, has bad miss under load, and sometimes backfires, unplugged the iac and held throttle cracked and made no difference. Unplugged o2 sensor and made no difference.

Any ideas to try?

 

What PCM are you using for the conversion?

 

A9L Pcm. I think

 

Pull it out and inspect the board!

I had 2 A9P PCM'S and 1 CW1 PCM that all had the capacitors leaking and one was only held by one leg. All had brown goo and green corrosion. I had all kinds of idle and surge problems, but the only code I had was for the ACT sensor.

Truck wouldn't idle without keeping my foot on the gas. The other one wouldn't connect with code reader.

 

I've hooked up the old computer when I went back to a stock later model cam. The cam that was in it was a comp failure in my book. Sounded good but it felt like it robbed me of 50hp. So I bought a later model one with the same firing order as the comp one and I installed it as I was doing front end work.

The old computer with the maf unplugged still had surging problems. And it ran fine when the computer was pulled and it was stored in a dry and clean area. I may pull it just to be sure but I would be surprised if it failed after 8 months from when they shipped it to me.

I'm going to test fuel pressure and injectors next but if that doesn't fix it I think my only option is to burn it to the ground.

 

Pulled the computer, took the case off and found nothing leaking or broken, this happened after I took the comp cam out, I double checked for vacuum leaks today with the smoke machine then pressurized the system to 10psi, and checked the fuel system and it still does it, I don't know what to try next.