Alright so I have a 1991 Firebird with the 5.0 TBI. The issue is that it ALMOST starts but it just can't for some reason. It will crank and crank all day but won't turn on. The car is CLEAN and I got it for a steal.

So I got the car from a guy who said it ran and drove about a month ago. He said since it started doing this thing, which is recent, he has since replaced the injectors and fuel pump. I can see the injectors working when we crank it. We also replaced the IAC sensor and when we did that it would even start but for literally ONE second then shut off. He said the distributor, plugs and wires are about 2yrs old.

So all in all between spark and fuel, it looks like its getting those. Im *guessing* its something related to airflow...but I don't know. Just checked the battery at O'reilly's just to be safe and they said its fine. Im totally open to suggestions and ideas. Thanks in advance for the help guys!

 

Nice car. I would check the ignition control module inside the distributor; most auto parts stores have a testing stand to check those.

Your problem sounds just like what happened to my '90 TBI Suburban a few months ago; it "wanted" to start, but couldn't. It was a bad ICM.

Also, buy a good spark tester. It will save you a lot of headaches in cases like this.

 

Alright, I took your adviced and replaced the ICM, but the same issue still exists. Any other guesses?

 

Could be a dumb suggestion, but have you played around with the timing at all? I know it won't start so you can't really check it, but maybe the distributor moved somehow?
Or more likely the ESC went bad and you aren't getting the advance you need? Easy to come by at the junkyard.

 

I have NOT messed with the timing at all. I asked the guy I got it from and he corrected me saying the car was drivable as of two weeks ago and he hadn't touched the distributor or wires. Besides, I just replaced the ICM literally yesterday, so if anything I would have felt the distributor move around as it sits. Whats killing me is that im sure the actual issue is something super stupid and easy to fix...I just need a day to take it apart and inspect it.

So I'm really getting WAY head of myself here, but I wonder if I can just swap out the 305 for a 350 and just ultra bypass this whole problem? I know its kinda like killing a fly with a rocket launcher but there's a guy selling a 94 Silverado engine near me for cheap...wonder if that would work?

 

I would have checked for spark before changing out the ICM. Also ICMs have been known to be DOA out of the box. Verify you have spark before changing/pointing fingers at other ignition pieces.

If you have spark you can suspect fuel. I noticed the can of starting fluid...are you giving it a squirt of that and then it acts like it wants to start? If a quick squirt helps what does a big squirt do? Longer than a second? I'd venture into testing the fuel pressure if the bigger squirt makes it run a little longer. I've often hear too many times...the fuel pump is new, ok what is your fuel pressure, I put a brand new fuel pump in, ok what is your fuel pressure, I just changed the fuel pump so it can't be that, ok what is your fuel pressure. It's also my understanding that the injectors can be changed without disassembling the fuel pressure regulator but before you point fingers again, what is your fuel pressure?

Another failure point is the short hose inside the fuel tank that connects the pump to the assembly. I've seen that hose being reused or the not rated for high pressure being used when a new pump gets installed. Over time it may split, the fuel dumps back into the tank and you lose fuel pressure to the injectors.

Here's a shot in the dark that can be checked really quick and I've only seen this happen one time. Buddies FSC had the stall out of the blue, after changing out the starter and battery as allegedly it cranks but on the slow side...turns out he had an alternator that was starting to seize up. Pull the belt and give it a whirl.

 

I'd check for spark. Check ignition and related fuses. Maybe even a bad ignition switch. And as above, see if it will run on the starting fluid.

 

Won't oil pressure sending unit cause a no fuel condition? Heard tales of cranking an engine over long enough to get enough oil psi to override the fuel cut out.

 

If the temp sensor goes out or loses connection on the front of the intake manifold it will not start..

 

SPARK PLUGS FOULED FROM TOO DAMN MUCH CRANKING?

Do you actually HAVE spark at the plug end of the plug wire? The suggestion to get a spark-tester is excellent. DO NOT buy one that has a light-bulb inside. You want the kind that causes the spark to jump an actual gap, not light-up some stupid bulb. I prefer the kind that is permanently calibrated for an HEI ignition, but there are some that have an adjustable gap.

What is the fuel pressure when cranking?

Connect a scan tool. Verify the computer is getting an RPM signal when cranking. While you're in there, verify ALL the sensors (can't verify O2 until the engine runs and heats it up, but you can check all the others.)

A failed coolant temp sensor can make for difficult starting, for example. Same with a disconnected or faulty MAP sensor. If the TPS sensor has failed in a way that sends a "full throttle" signal, the computer will stop spraying fuel, and it'll never start. ALL the sensors have to be working properly (except O2) for good starting.

 

My apologies for not replying sooner, I havent gotten ANY Email updates that people have been replying. In any event, since I last checked in, I checked the sparkplugs and the distributor - all solid.

I did notice that no fuel was spraying anymore though so I went ahead and rebuilt the throttle body AND replaced the injectors. I also replaced the fuel relay on the firewall since the sending unit also quit firing on me. So all that done, Im getting fuel at the KEY ON position, and when I crank it up, it will start and stay on for 1-3 seconds. Charged the battery, its old, but holds a decent-ish charge still. Oh and while I had the throttle body off, I went ahead and replaced the EGR valve too. I figure its probably worth replacing since it was as old as the car lol. In any event, back to square 1.5(?). We got spark, and fuel, and about 3 seconds of runtime lol. For what its worth, one of the local shop owners said he'd check it out for me this week and help me narrow the remaining list of problems down since he has all the scan and timing tools and I don't. I'll see how that goes and let you all know. Thank you everyone for pitching in!

 

Runs for two--three seconds, then dies? That's the symptoms of a failed security system. Do you have a "Security" light on the dash?

Also, running for a couple seconds might be a failure for the fuel pump to run. The computer may prime the pump for two seconds, but not run the pump after that. Connect a scan tool, look at the data stream. Does the computer have an RPM signal when cranking or for the couple seconds that it runs?

 

The security light is on, but the guy was driving it up until 2 weeks before I bought it. I mean I guess he could very well have been lying, but then again the ignition keys don't have the solenoid, and I thought the vats would prevent it from starting at all?

 

Solenoid?

You mean the resistor in the key?