3.1 TBI running rough

[patgizz]

ok, my 90 APV (3.1, iron head, FWD, TBI, 130k miles) all of a sudden a while back decided to quit running. it would run if we squirted gas down the TB because the injectors were not firing. here is what i did:

changed fuel filter - no change

checked injector pulse w/ noid light - good pulse

changed ecm w/ spare - no change

changed to a spare super hi mile pair of injectors - ran but rough

rebuilt my TB and put in a new regulator w/ 2 new injectors - ran much better but still too rough and stumbled upon acceleration

new plugs, wires, cap, rotor, coil - no change

new o2 sensor - runs a little better warm but still rough and stumbles

all this time it has not set the check engine light or stored any fault codes


any ideas where to look next? plugged cat converter?

[geoffinbc]

Check the engine coolant temperature sensor. Should have a resistance of 3400 ohms at 31*C (70*f). If not replace it

Cat is a possibility un bolt it and run open pipes to see.

What is your fuel pressure? Needs to be 9~13 PSI in order to work right.

[DEI37]

9-13psi for fuel pressure on a fuel injected motor? Carb'd maybe, but a typical fuelie requires 35+ psi.

[patgizz]

this is TBI - low pressure system

[geoffinbc]

Exactally. TBI is pretty much a glorified carburetor anyway. But yea in the range of 9~13PSI is correct. 11 probabally being the most optimal.

Im gonna say really check out that temp sensor. Especiall with no codes. Only buy GM on this one. There was a person who bought a temp sensor for his truck (I think it was at Sutozone) and checked its readings after he bought it and it was WAY off out of the box. So the next time he went he took a multimeter and tested it. If you test at room temperature you should be close to 3400 OHMS

[montecarlols(z31)96]

check you fuel pump, or the cat

[patgizz]

im gonna just replace the temp sensor with a known good one(pays to have a running parts car) and hopefully eliminate the problem(worst case i eliminate the sensor).

[patgizz]

ohmed out the temp sensor to right around 3400 at room temp so that is not the problem.

right now its too damn cold to lay on the ground and unbolt the cat, or do anything more involved than running outside for more than 5 minutes.

[geoffinbc]

Ok back in the days of gmforum there was a huge thread about this. Me a Charles9C1 (TBI Caprice) found that his problem was electrical. He eventually took it into my dads work and found that there was several corroded connections that he couldn't even see. I would suggest removing all the power and ground connections and cleaning them and adding some die-electric grease. If it turns out not to be the problem well at least you improved on things and did some preventative maintenence.

[patgizz]

thanks for all the help so far. my buddy is bringing over his fuel pressure, compression, and leakdown testers tomorrow. we will check all that. when i got the van i had a problem with power wires, all the links at the starter were corroded because they are right down getting blasted with road water, so i made a new harness to pull power directly from the battery and ran all the vehicle power leads away from down there and mounted a distribution block up on the strut tower so i know all my +12v are good and clean. will check the grounds as well when we are doing the other tests.