Fuel Injection Problem

[tloftus]

Hey all, it's been a while since I've posted here. I sold of my 89 Cutlass (3.1L) to my brother in law about a year ago and now he's having problems so guess who gets to work on it. He brought it to me on a tow truck, wouldn't start. Checked fuel pressure and it was around 20PSI, replaced the fuel pump and filter, back to around 40PSI and now will start but will not stay running or will die when you put a load on the motor. So 4 days later of checking vacuum lines, sensors, etc I have finally had a breakthrough.

 

Under the hood in the fuse box there are two fuses for injectors, one controls the front three, one controls the back three. (I'm not sure which does which yet.) I pulled both, they are both good fuses. I started the car pulled fuse A, the car immediately died. I put it back in, restarted, this time pulled fuse B and the car actually ran BETTER! I can put it in drive now without it dying. Obviously something is not right in the idle but it is better than I was before.

 

Now, my question is.. how does removing 3 injectors from semi-operation (because if they weren't working at all pulling the fuse would have had made no difference) cause a motor to run better? What could the problem be with them?

 

I know there is two control lines out of the ECM, again, one for the front 3 and one for the back 3. I would suspect a fuel issue would affect all 6 injectors, the only thing I can think of is maybe one of the control lines out of the ECM is shorting to ground or something or there is something wrong internally to the ECM.

 

Sorry for the long post, trying to give as much detail as possible, appreciate any help!

 

Thanks as always.

 

Tom

[89GP_SE]

Well, you say that you are around 40 PSI.... that number should be closer to 50. Also try removing the vac line from the fuel pressure regulator, hold your finger over the vac line, and see what your pressure goes up to, should be 55+ with the pressure regulator unhooked. Sounds to me like you have an open(stuck) injector or bad FPR.

 

Also what I was told about these FI systems was that it always pulses two cylinders with fuel, but only one cylinder fires. So for ex. If number one is firing, number one and number 6 injectors are pulsing.

 

Good Luck.

[tloftus]

Thanks for the reply, I have some more information. I pulled the connector off the ECM that controls the fuel injectors, one reads 12 volts, the other doesn't! Chances are there's either a wire making contact or a shorted fuel injector causing the 12 in on the injector run right to the 12 out??

 

Thanks,

Tom

[Imp558]

I looked it up for you. Fuel pressure should be 40.5 - 47 lbs with the ignition on and engine not running. Resistance should be 11.8 - 12.6 ohms on each injector. Could try swapping the injectors and see if the condition follows them.

 

[rockfangd]

sounds like the ecm could be the culprit

[slick]

Well, you say that you are around 40 PSI.... that number should be closer to 50. Also try removing the vac line from the fuel pressure regulator, hold your finger over the vac line, and see what your pressure goes up to, should be 55+ with the pressure regulator unhooked. Sounds to me like you have an open(stuck) injector or bad FPR.

 

Also what I was told about these FI systems was that it always pulses two cylinders with fuel, but only one cylinder fires. So for ex. If number one is firing, number one and number 6 injectors are pulsing.

 

Good Luck.

 

40 psi is fine for idle.

 

If you still have the fuel pressure gauge available, hook it back up, and put the car in the ON position (do not start), and watch the fuel pressure gauge. It should hold pressure. Check back on it in 5-10 minutes, if it's still holing pressure well, then your fuel pressure regulator is fine.

 

If your pulling a fuse and it actually runs better, I'd suspect that something may be up with the injectors. Unplug each injector, use a multimeter, and ohm out each injector. They should all be within .3-.5 ohms of each other, in the 11.5(low)-13.5(high) ohm range. If they are not, wouldn't be a bad idea to replace them.

 

You can also do this while the car is running, unplugging each injector one at a time. If the car seems to run better afterwards, you may have found that culprit injector (out of the ohm range, or even shorting out).