1991 Trans Am 305 TPI...Sometimes my fuel pump wont prime or turn on, so my car wont start. Here is what I have tried to fix the problem. New fuel pump (that has been tested good and works sometimes), fuel pump relay, oil pressure switch, and the fuel pump fuse. The sypmtons are:

my car only starts when i hear the fuel pump come on prior to starting.

when my car wont start, I can not hear the fuel pump prime before starting.

Does anyone have any ideas? Could it be my VATS or a short somewhere or what? Thanks for your help.

 

Does your car crank over though? If it does, then it's not VATS.

Your car needs fuel, air, spark, and compression to run. You're obviously getting air and compression- but double check to see if you're getting a spark before you rule out the fuel as the problem. Your car won't always prime if your lines are already pressurized.

 

So can you kind of tell me what to check and how to check it the next time it wont start? Thank you for your help token. I believe that the dist. cap rotor and the ignition coil have been replaced recently.

 

and also, it is cranking over. Its just not getting fuel i believe since it starts some of the time. Any help would be great. thanks

 

If it's not cranking, it would be your VATS or neutral safety switch. But if it is, then I'd imagine it would be an ignition problem over a fuel problem since you already replaced a lot of stuff. I'll walk you through some steps to check. Just a quick question- how old is the fuel pump? Are the lines intact also?

Pull off the coil wire and get it close to the fender or cowl. Try starting the car and see if you've got spark. You don't want to be holding this wire when doing it, so if you have to weigh it down with something use a plastic object as not to prematurely ground it. If it doesn't spark, that means you've got a problem with your coil or your spark control module.

But if that works that means your coil is good. Plug it back in and pull out a spark plug. Put it on something metal also such as the intake or again the cowl. Make sure the side is touching the metal. Start it and see if you're getting a spark from the electrode. If you're not getting a spark, it means the ignition module in your distributor is probably faulty. They're like $10 or so.

It's doubtful that it's a problem with your spark plugs or wires since the problem is only intermittent, however it wouldn't be a bad idea to check the resistance with a multimeter while you're out there.

After you've ruled out these things and you are assured you're getting a spark, then it's a fuel problem as you suspected. The first thing I would do would be a temporary suggestion just to confirm something... Pull the fuel pump relay out and jump the gray wire with +12v. Don't put the relay back in, just give the gray wire the power. This will turn your fuel pump on. You will hear it whine. If it does not, you have a problem with your fuel pump itself. If it does, your fuel pump should be okay, and I would assume it's a problem with the relay or oil pressure switch, or a short in the wiring.

Again, if the car does start with this temporary fix, you should replace (or at least have a parts store test) the two aforementioned parts again. You will be able to drive it at least, however if you got in an accident your fuel pump would not shut off. Just food for thought.




Let us know what happens!

 

Well, I have replaced the fuel pump relay and oil pressure switch and have replaced the fuel pump twice to make sure it wasnt a faulty unit. when my car is wanting to start, I am getting power to the relay, fuse, and fuel pump. I have to wait until it wont start again to see if those things are getting any power.

So the next time it wont start, you want me to take off the coil wire from the distributor and hold it up against my fender and see if it is sparking, and then pull off a spark plug wire and hold it to a fender and see if it is sparking if the coil wire is okay. I am thinking of getting a new coil anyways, any suggestions on that? Also on a good cap and rotor? its a 305 tpi.

 

Yes sir. That's what you should check, because to me it sounds like an ignition problem, considering you've already replaced things for the fuel system.

If you go with a new coil, you can't go wrong with the MSD blaster coil. It's about $38 from www.summitracing.com . I don't have a part number but I can find it if you'd like. Or try a search. Cap and rotor, I always used standard OEM replacements. But once again, MSD is good stuff.

Hope that helps!

 

thanks, i will do what i can and send you a pm letting you know what i find out.

 

Remove the dist cap and look for burnt/corroded connections from the pickup to the ign module. Inspect the pickup coil, if the insulation and leads look bad replace the pickup. I would replace both items. If the ign module is OK remove it clean off the metal backing of the module and the dist base and recoat the module with fresh dieelectric grease.

 

There is some good troubleshooting advice in this thread, but I think I'd be more inclined to attack the fuelpump circuit first...only based on the original poster saying

"Sometimes my fuel pump wont prime or turn on, so my car wont start."

If it were my problem, I'd begin at the source for voltage, cleaning connections, etc, along the way since it's intermittent. I also wouldn't rule out the possibility of a poor ground contact either.

 

Thank you so much for the help. The next time it wont start, what should I do to check the electrical connections, where do I start and what do I do from there? I have a 12V test light that I prefer to use. Thank you.

 

I'd start withe Chlitons/Hayne manual and go over the FP schematic, then locate places to probe...IIRC, power is delivered from a 30?amp fuse up by the battery, then goes to the FP relay and to the oil pressure switch.

See, if even if the ECM isn't firing the FP Relay, after a few seconds of cranking the engine, the oil pressure switch should supply power to the pump (assuming it's good) and allow the car to start and run.

You may be able to monitor fuel pump voltage through the ALDL, but you need to look at the pinout to confirm...i/e put your light into one of the pin, turn the key and see if voltage is there for a few seconds, if not, se if voltage comes after some cranking...this assumes that one of the pins can monitor it, I don't remember for sure and my manual isn't close by.

 

The fuel pump voltage is monitored at terminal "G" of the ALDL connector, looking at the front of the ALDL bottom row last pin on the LEFT is "G". You can place the test light to that pin and see if you have voltage. I went through a similiar thing with my 89 Camaro. Remember, the pump does not always go through a prime cycle. To get it to do the 2 sec prime, relieve the fuel pressure by loosening the gas cap and pull the ECM pigtail for 30 sec. Then put in the test light and turn on the key. If you want, you can feed 12 volts from the battery thru a 10 amp fuse to terminal "G". That bypasses everything but the wiring to the pump assy itself. You can do that test with the key off so you can hear the pump. As the previous post said, the pump gets 12 volts from 2 things, the relay and the oil sender switch. The switch in the sender closes after the engine has 4-5psi of oil pressure. If you get it to run you can test the oil sender sw by simply unplugging the relay while it is running. If the engine shuts down most likely it is bad. Also, and this is where I got fooled, once the pump goes through prime cycle subsequent starts work like this. When you crank the fuel pump relay will not energize unless the ECM sees reference pulses from the dist pickup. If in fact the oil sender is bad then you will think there is a voltage or wiring problem when it is something entirely different. I changed my pump unnecessarily because I was relying on what I heard as opposed to troubleshooting it. WELLLL, it was 15 yrs old is my only defense for being stupid Also, I am pretty sure the injectors won't fire if the dist pulses are gone. Good luck!

 

Finally, my car wouldnt start, so I was able to diagnose it a little better. What happened was, I went out and started my car, the fuel pump primed fine, motor ran good and strong. I took it out for a drive just to see what was going on, maybe drove 1 mile in total. Once I got back, I parked it, shut my car off, waited a few seconds, tried to start it again, and it wouldnt start...as matter of fact it wouldnt even crank over. after a few minutes it was cranking over but not starting. i then popped the hood and I was getting voltage to my fuel pump fuse, and back to my relay. but still no start. (I could hear the fuel pump relay click when the key was turned to run). The oil pressure switch is new. Now I am starting to think it is a VATS problem since it wouldnt even crank over. Any ideas now? I am lost. Thanks.

 

VATS should set a code ..50-somthing, IIRC. VATs disables the starter enable relay and the injectors. Pull your codes, unsure if VATs can get confused and disable the injectors while cranking??

 

what does IIRC mean? i have a GM code detector that flashes the check engine light, should I use it?

 

Look at the "security" light, if it comes on for 2 sec and goes out it is normally not a VATS problem. Your code reader is fine to use.