91 Century 3.3l injector wiring problem

[schwanracing]

I am working on a 91 3.3 150000mi. It will start and run after sitting for a while but it will only run for about 30-45 seconds. This car has been to two shops before me and no one could figure out the problem. I dont know alot of history besides the ecm was replaced and upon visual inspection i noticed that wiring to crank sensor has been replaced. After the initial run time the car will crank but no fire. Checked codes and get 22 and 34. Out of curiousity i removed plug to tps and checked voltage had 5 volts and checked voltage at maf and had 12 volts. I then removed air cleaner and sprayed starting fluid and the car started right up. I pulled injector wires off and installed noid light and found that it wasnt lighting up at key on or during cranking, so i took a test light to battery ground to pink injector wire and with key on or cranking the test light stayed lit with no pulse during crank and same for blue wire so i checked voltage with voltmeter and injectors have battery voltage with key on or during cranking on all 6 injectors. Any ideas on where to go from here will be greatly appericiated

[schwanracing]

ok, i wasn't thinkin when i checked them i guess. with all the other injectors plugged in i guess this would be normal because of the way it is wired, right??? i unplugged all injectors then checked with noid light and all seem ok. Ill be checkin fuel pressure in about 20 min the ill post pressures.

[maxwedge]

I would check the resistance of all the injectors, if one is shorted it will kill the circuit to the others and no pulse.

[Tech II]

Max seems to be on track with this one....each injector should ohm out at 12 ohms.....

[schwanracing]

Ok i will check that in a min. Fuel pressure with key on is 42 cranking 40. Goin to check fuel injector resistance now and ill let ya know. Could this be a timing issue???

[schwanracing]

Ok i had 12ohm +/- .03 ohm on all except #1 which had 10 ohm and # 2 which had 2 ohms.

[schwanracing]

I went back and left the #2 injector unplugged and started the car. It fired right up and ran longer than ive seen it run. So while running i plugged inj. 2 back in and it instantly died. So thats most of my probs got to go get another injector then ill check and see what idle speed is doing cuz right now its idling at about 2000 rpms just by listening. I cant thank you two enough lol you prob just got me a lifetime customer over this one THANK YOU!!!!!

[maxwedge]

Your are welcome, Tech11 is on his game, sometimes you need to step back and think the pcm does, plus just plain experience. That low resistance injector pulled down the current to fire the other 5.

[schwanracing]

Your right and again ty. But i got the injetor changed replaced all orings on other injectors which were extremly bad and test drove. it does good except at idle seems to have a miss in it but ne thing past idle seems fine. Not sure but appears that the idle screw has been messed with recently but as far as idle speed now it seems fine. i know these are known for a rough idle but still think its got another issue. Think my best bet is to start at square one again and check everything

[maxwedge]

If someone played with the base idle the tps will be out of range. They do idle poorly, normal.

[Tech II]

Any tech that has worked on a 3.3, will tell you they idle like crap, some worse than others....it's just the nature of the beast....above idle and on the highway, this engine is a bear.....I always felt, the 3.3 had more power than a 3.1, displacement aside....

I remember a brand new Century station wagon came to the shop......it felt/sounded like a misfire at idle....checked everything, could find nothing wrong....did a bulletin search....nothing....finally, got a hold of the right technician at TAC.....I called previously about the problem, and was told to just check the basics, because there was no "listed" problem.....called again, and the Tech laughed because I was chasing my tail.....told me how these engines, under the right conditions, could feel like a rough idle....just raise it a bit and it goes away.....said it was the way the engine was designed(this engine did not have an EGR) and the programming in the ECM.....he said they could have programmed the car to raise the idle, but then the car would be jumping into gear when you shifted into drive....so they took the lesser of two evils....

So if you don't have a definite misfire, and it goes away just off idle, forgetaboutit.....

There is one possibility.....chased my tail on on a Firedbird, once.....came in with a slight misfire at idle only.....could not find the problem....asked the guy how long he had the car....said he just bought it from a private party....gave me their number....called to see if there were any problems with the car......said it had a bad misfire, and after 3 garages, had changed all kinds of parts, the last one replaced a bad injector....while it made the car run much better, it still wasn't quite the same, as it was before the problem started, so they sold it....of course they never mentioned it to the new owner....and the new owner drove it like this for 6 months(so much for just buying it) before doing anything about it...

Spotted the new injector, and did a flow rate test on all.....the old ones were within spec, but on the low side of the spec....the new one, was on the high side just outside the spec.....so my guess was the new injector caused an imbalance in the engine with one cylinder getting slightly more fuel than the rest....Told the guy, he had an injector problem....and the only way to fix it was to get all new injectors, so that they would be matched, and have the same flow rate....he agreed and that took care of the problem....

I'm not saying that is your problem.....it's just a possibility.....you need special equipment to test flow rates in injectors, which I think only a dealership would have....the thing is, If just slightly raising the idle takes care of the roughness, I wouldn't worry about it....