I am going to try to keep this short and to the point. So here it goes... I got my 91 GTE back on the road about a year ago. It has Stage 2 BC cams, Lex/560 mod with afpr, a 57 trim driftmotion CT26 turbo, adjustable cam gears, and the Morganson C.O.P. setup. Other than stronger internals and the aforementioned components it is stock. While I am going down hills or at any point where there is not a load on the engine, in boost or otherwise, the engine bucks and it feels equivalent to someone driving a stick car for the first time and trying to take off in first. As soon as I put a load on the engine, the problem goes away and the engine smooths out. The motor will also hesitate until it hits roughly 2000 rpm and then it revs perfectly while it is cold. It hesitates worse when the engine is cold, but it is not much better when it is warm.
So far I have adjusted the fuel pressure thinking it might be loading up on fuel, but no change. I have checked the TPS to make sure it was functioning correctly and set properly which it is. The MAF is brand new as well as coils. I should say this now, it was doing the same thing before I switched it over to the C.O.P. setup and the reason I switched it was because one of the three factory coils was bad and I wanted to do the conversion anyways. I checked the IAC thinking the hesitation off idle, and the erratic idle might be caused by the IAC, but it is perfectly within specifications. I have checked a few times for vacuum leaks, because I did have one, but since I fixed the one, I haven't discovered anymore. I have also checked the CPS and it is about 40 ohms out of resistance across all terminals and it has a slight amount of oil coming out through the center. I am leaning towards the CPS being the issue, but I have zero codes from the computer indicating anything is amiss. All of my diagnostic procedures and specs came from the Cygnus X1 TSRM. My question is, is it possible that the CPS could be causing all these issues while the computer has no idea about it. I realize pre-96 OBD systems are incredibly stupid by comparison, but considering what I have discovered and the problems I am experiencing I figured the computer would realize something is wrong.
Any help is greatly appreciated and if I left some important detail out, I apologize now. It has been one hell of a day.
So far I have adjusted the fuel pressure thinking it might be loading up on fuel, but no change. I have checked the TPS to make sure it was functioning correctly and set properly which it is. The MAF is brand new as well as coils. I should say this now, it was doing the same thing before I switched it over to the C.O.P. setup and the reason I switched it was because one of the three factory coils was bad and I wanted to do the conversion anyways. I checked the IAC thinking the hesitation off idle, and the erratic idle might be caused by the IAC, but it is perfectly within specifications. I have checked a few times for vacuum leaks, because I did have one, but since I fixed the one, I haven't discovered anymore. I have also checked the CPS and it is about 40 ohms out of resistance across all terminals and it has a slight amount of oil coming out through the center. I am leaning towards the CPS being the issue, but I have zero codes from the computer indicating anything is amiss. All of my diagnostic procedures and specs came from the Cygnus X1 TSRM. My question is, is it possible that the CPS could be causing all these issues while the computer has no idea about it. I realize pre-96 OBD systems are incredibly stupid by comparison, but considering what I have discovered and the problems I am experiencing I figured the computer would realize something is wrong.
Any help is greatly appreciated and if I left some important detail out, I apologize now. It has been one hell of a day.