Help me troubleshoot my engine swap project. I did the swap about 8-9 years ago but never actually completed it. Now I am back into it and having some trouble that seems to be misfire related.
The parts: '99 GTP 3800SC 4T65HD that came with engine VS cam 3.4 pulley Evap delete boost bypass delete 2nd (rear) O2 delete FastFiero PCM Suppertrapp muffler fuel pump was replaced with aftermarket for more pressure, I dont recall which one.
Issue with car is it stumbles or misfires at idle, sometimes enough to set a P0300. While driving it there isn't much power above 1/4 throttle and misfire gets worse. When not driving the engine revs up great with no misfire.
I can scan the car with Carcode (Alex Pepper). I am currently getting -15 to -20 LTFT at idle. I had the injectors tested and cleaned, two failed. I replaced the bad ones and it runs better, but same issues persist. Actually the fuel trims went even more negative than previously. Changed plugs, swapped plug wires around, swapped ICM coil pack with used one.....no change
I cleaned the MAF. When I scan it the values change with RPM, about 2460HZ at idle.
I did not change the O2 sensor yet.
Fuel pressure regulator is not leaking. Pressure at idle is about 42. Car off around 50.
I changed the Crank Position Sensor, no change.
Did a compression test: 1 140 2 120 3 130 4 150 5 130 6 150
Negative fuel trims will suggest you are somehow injecting too much fuel... and not much else will cause those readings. This typically will only mean you have too much fuel pressure or the wrong injectors. Can you confrim they are stock injectors? Have you attempted running without the o2 sensor to verify that you are indeed spraying too much fuel? It should run worse after you clear the fuel trims and remove the o2 sensor as it will be adding almost 20% more fuel at that point.
The injectors came with the motor- I assume they are stock.... The part number is 24508208 on one side and 0280155811 on the other side. Which according to Google is probably 36lb at 42psi. The the injector service report indicate that they flow 38 lb/hr at 3 bar and 2500 rpm.
I just sent my PCM off, so I cant test the O2 response for a week or so. I can say that when I was driving it around the fuel trims always stayed negative. They would get close to 0, but never quite made it. It does seem that the PCM is trying to reduce the fuel at idle, and the rest of the band for that matter. It is possible the PCM had been programmed with the wrong injector flow rate- I should know that soon.
[This message has been edited by Ken_86gt (edited 09-24-2014).]
The injectors came with the motor- I assume they are stock.... The part number is 24508208 on one side and 0280155811 on the other side. Which according to Google is probably 36lb at 42psi. The the injector service report indicate that they flow 38 lb/hr at 3 bar and 2500 rpm.
I just sent my PCM off, so I cant test the O2 response for a week or so. I can say that when I was driving it around the fuel trims always stayed negative. They would get close to 0, but never quite made it. It does seem that the PCM is trying to reduce the fuel at idle, and the rest of the band for that matter. It is possible the PCM had been programmed with the wrong injector flow rate- I should know that soon.
If the trims are close to 0 like (-3) but never get there during cruise conditions then that is a good safe tune. They should lock at 0 during WOT. If they are negative double digits then u are getting too much fuel or poor spark. That is if the o2 is in good working order and u don't have a mechanical issue.
Originally posted by nosrac: If the trims are close to 0 like (-3) but never get there during cruise conditions then that is a good safe tune. They should lock at 0 during WOT. If they are negative double digits then u are getting too much fuel or poor spark. That is if the o2 is in good working order and u don't have a mechanical issue.
