Idle Fuel Cut???

[mitsubluetalon]

Hello, i have a little situation on my hands. i just finished doing a head swap from one with bent intake valves to another head that used to belong to a non-turbo engine. i simply put my turbo cams in his non-turbo head and it worked.........

my problem now is that the engine does not run properly. meaning that the idle is erratic, almost as if it is sputtering, or out of timing, and it has even stalled once. the idle would sound almost smooth for a second and then go back to sputtering.

now if i rev the engine, most of the time it will get to 2000 rpm and then something happens like a fuel cut and the rpms drop down to about 1000, then it will go back up to 2000 and oscillate like that even when its at WOT. the odd time it will get past 2000 and after a second of higher revs theres that fuel cut or something and then back to the 1000-2000 oscillations.

i have not done a boost leak test but that is going to be the next thing i check. my list of suspects includes the throttle body, some kind of vacuum leak, or the ECU.

the thing with the ECU is that i swapped mine out because of leaky caps. i found one on e-bay that was meant for a 90 DSM. i think it was a galant. the add he put up said it would work on any 91-94 turbo talon, laser, or eclipse as long as you swap out pins 14 and 6. i did so. fired her up and she ran but with this problem i'm having.

about 2 mins after initial startup with the new head, the CEL came on. i checked the codes and it was for idle position switch and the barometric pressure sensor. I next checked what the pins i swapped were for and sure enough those were the 2 pins. I then switched them back and fired her up again. same idle issues, but no CEL!

I don't have dsmlink yet so i can't check out my fuel curves but i was just thinking that maybe the ECU can't sync up to this engine by swapping those pins alone. for now i'm going to start ruling out my suspect list.


thank you very much for your time..

Jason.

 

[mitsubluetalon]

does anybody know what would make a dsm engine sputter, or idle rough, and have that fuel cut at 2000 rpm??

If it were a boost leak, say on my intake manifold, would that cause the rough idle, and that fuel cut at 2000 rpm?

 

[skelly]

My 90 is experiencing a similar, but slightly different problem. I don't think I have the fuel cut that you seem to be having, but it does the same seemingly normal idle for 1/2 to 2 seconds and then sputters. I was thinking that perhaps the sputter is some sort of miss, ignition related, but I'm still not certain.

In an effort to nail down this problem, I've done a partial tear-down and gasket/consumable replacement which I've detailed here. Now I'm positive that there are no vacuum/boost leaks. I've also replaced leaking capacitors on the ECU, so that is not the cause. I've tested and replaced ignition components, so that is not the cause. I'm down to the following possibilities which I hope to narrow down or finally pin this weekend:

1) Knock sensor
2) Ignition timing
3) Gummedup/sticky injector(s) (the car was sitting dormant for over a year)
4) Possibly the O2 sensor, but i really doubt it at this point

I think between those three my problem will be resolved. I'm hoping it's not the knock sensor because those are a bit pricey to replace.

HTH
- SK