Possible TBI (Injector) Problem.. Help needed

First off, the car is an '89 Caprice "9C1" (Former police vehicle). It's also equipped with a 350.

I was driving home this evening and the car just up quit for no reason. Upon having it towed home, I began diagnosing it. The first thing I noticed was that I get no Service engine soon light upon turning on the key. The Fuel pump also does not prime when I turn the key to RUN.

Suspecting a faulty fuel pump (which was just changed last year), I check the voltage at the harness in the rear.. I get 12v. I check all the fuses and all test fine. I move to the fuelpump test connector, and connect 12v to it. I hear the fuel pump whine, so it's still working. Just not with the EEC.

I check out the fuel pump relay and it seems to test out fine, except for the lack of the automatic fuel pump prime upon turning the ignition to RUN.

Suspecting a clogged filter, i disconnect the line in front of the fuel filter and prime the pump manually. Fuel drips from the front of the filter, so no clog.

I move farther forward and disconnect the fuel line going into the TBI. I manually prime the pump and fuel squirts out from there. So the only thing left after that is the two injectors. Upon keeping the fuel pump on by overriding the test connector, and trying to crank the engine, i get absolutely no mist from the injectors. If I pour fuel into the TBI, it'll run until the gas is gone and then die. So I know i'm getting spark and supposedly the EEC (other then the fuel delivery) seems to be working properly.

Does anyone have any suggestions on what to try? One other thing I should mention is that it's always had a surging idle problem that would come from time to time. It would just from 800-1200 rpm randomly at times just sitting at idle for no reason. I suspected the MC solenoid, but i'm never bothered with it because it would only do it every so often. Looks now like something finally gave up. I'm pretty sure I have it either narrowed down to the EEC/PROM or the injectors themselves.. although im not sure how they would just up and die.

Any responses or ideas would be greatly appreciated.

MC solenoid - do you mean IAC? The MC solenoid is found on feedback carburetors. I would suspect that your car might be having ECM issues. First off, verify that the SES bulb is in working order - if it is not, this will cause an ECM fault. If the bulb is good but the SES light does not come on, I would suspect an ECM failure.

Si-212 is correct (as usual). The ignition will operate without a working ECM, so as long as you manually administer fuel, it would run. The lack of an SES lamp is key. If you are supplying 12V to the 'G' terminal of the ALDL to operate the pump, it bypasses the ECM but uses the NC contacts of the pump relay to power the pump.

One possibility is that the ECM/Fuel Pump fuse (20A ATO type) has failed. These are frequently not in the main fuse panel, but located in a single fuseholder along the inner fender, near the battery. That would prevent both pump operation and ECM operation.

Thank you for the replies!

Is the lack of an SES light really that important in keeping it from running? Meaning that if it is burned out, it will keep the entire car from running? I did notice when I turn on the key, I dont even get a flash from the SES light, and when I try to jumper A & B on the ALDL to enter the diagnostic mode, I dont get a light at all like I usually do.

I did check the 20A fuse under the hood next to the fuel pump relay, and it checked out good, even with a continuity tester. I'm going to check the other fuses under the dash again and see if I can find the problem. I was really hoping it was the 7.5A ECM fuse, as according to the schematic, it's one of the main fuses that controls the injectors, which seems to be my problem.

Also, one other thing I noticed. I was looking at the ECM. And the code on the sticker says "APFN", yet the code on the PROM itself says "ATJP". Every other computer i've ever worked with always had matching codes in both places, and it usually causes problems if they are different. I was unable to find a reference anywhere as to the difference of these.. but the car has ran fine for two years with it, so I dont think its causing any problem.. just wanted to add that in there.

I'll keep you guys updated throughout the day, I really need to get this fixed before tonight, so hopefully it really is as something as small as a burned out SES light.

P.S. No wonder I could never find the MC Solenoid. The Haynes book I have swears up and down it has one, but it also covers 21 years of cars.. so it's no wonder.

Well, I pulled the SES bulb out and checked it, and it tests fine. I replaced it with the "fasten belts" light (which I know works), and still nothing.

I'm going to go back and check fuses, but if the car will run fine as long as I keep dumping fuel into the throttle body, then I can't see any fuses being the problem.

Any other suggestions of things out there to check? Is it possible it could be the fuel pump relay? Even if the SES isnt lighting? Or does is still sound like an ECM issue? :(

ECM all the way.

If you don't even get the SES "bounce" when you power up the ignition, the ECM either isn't getting power, or it's damaged. IIRC, it should be a '747, and they're pretty common.

I'd like to thank everyone here tremendously for all the help. The car is running better then ever right now, and I'll explain what I did.

After checking all the fuses again, I took out the EEC and checked out the connectors. First thing was that the pins were all a green corroded color. Think of a tarnished penny....

After that, I checked out the pins... :eek:

Two of them were missing! After looking at the schematic, one of them went to the transmission position switch, and the other... the EEC power!

I checked the connectors, and sure enough both pins were broken off inside. After taking them out, and picking up a new EEC from the local pick & pull, I reconnected the battery, turned the ignition on.. showed a SES light, cranked it over and it fired right up! :iceslolan

I'm just glad it was the EEC power pin that decided to break, and not a few of the sensor pins, where I would have been chasing around and replacing all the affected sensors.

Thanks again for all the help guys, I really do appreciate it! Glad to see such a great group of car-guys, let alone ones with experience with the caprice. :)

i'm having a simular problem on my 1991 chevy truck... all of a sudden it stopped spraying fuel... any idea where this connector would be on my truck? it has the TBI system on it... i've checked everything like you did... just can't figure it out