Idle Surge And Stall After Warmup...

[Nathan Reible]

Hello everyone, just signed up here. I just bought an 89 GT hatchback (AOD) about a month ago. At some point during it's life it was converted to a carburetor, not sure when. The person I bought it from rebuilt the motor (400 miles on it now), put forged pistons in it, a cam and lifter set (he couldn't remember what model, duration or lift it was which is pretty frustrating), and converted it back to EFI but really didn't get all the wiring straight...so I've been messing with the wiring for the past month. It has an A9L in it, MAF, etc, and I first tried to use a 90 EEC harness which proved to be a real nightmare...I had to wire a switch to the fuel pump, ran like crap, etc. I was able to find an 89 harness on Ebay and just put it in a few days ago, I took the MAF harness from the 89 wiring and hooked it up (Pin 37, 40, 9 and 50) and relocated the VSS wires to Pins 38 and 32. While I had the upper intake off I installed a set of Bosch 30lb injectors (red, 4-hole). My fuel pump issues are solved, primes the system like it should when you turn the key, and it starts right up, but it seems to idle a bit rough...then when it starts to warm up it surges like crazy (from 500-1200 RPMs) and eventually stalls. Throttle response is horrible and if I mash the throttle it backfires...it almost runs worse now then when I had the 90 harness in it. The interesting thing is, when I unplug the MAF the idle stabilizes, it still runs rough but doesn't surge and stall.

I have a feeling the MAF is bad, and putting larger injectors in the car doesn't help a thing. I've already cleaned the throttle body and IAC, but haven't touched the TPS. I'm about to go get a test light so I can run the codes to see what's going on. I thought I would post the symptoms though and see if anyone had any ideas or suggestions. Thanks!

 

[88LX5.Oh]

Bigger injectors do NOT give power. That's one of the most common misconceptions I hear. Bigger injectors SUPPORT more power.
Also, bigger injectors and nothing said about a calibrated MAF?
Put the stock injectors back in unless you wanna throw $200+ on a calibrated MAF sensor. One final note, factory injectors can support up to like 300 crank HP so unless you're going to be doing a bad as* head, cam, and intake swap in the near future, put the stockers back in.

 

[Jace78]

^^ what he said, your injectors are the problem, or the fact you did not upgrade MAF. If you have the stockers but need a rebuild click here and rebuild

 

[Nathan Reible]

I plan on doing a power adder of some sort in the future...I guess I could just keep the stock injectors in for now. I just got them for a pretty good price so I thought I'd grab them ($60). I had a feeling that was the problem, thanks for confirming it though guys, I appreciate it.

 

[88LX5.Oh]

I plan on doing a power adder of some sort in the future...I guess I could just keep the stock injectors in for now. I just got them for a pretty good price so I thought I'd grab them ($60). I had a feeling that was the problem, thanks for confirming it though guys, I appreciate it.

No problem! Keep us updated. We here on SN like reading material lol