TBI guys.....I need your help.

[texassquarebodies]

I have a 1987 crewcab 350/400th truck. It quit running a while back. I can put either in the tbi and it will start for a sec, until the either is out. Where do I start looking for my problem at? How do I test the fuel pump relay? How do I see if the pump is bad? Injectors are not spraying fuel.


You guys help me fix my other tbi truck.....Thank You !!!!

[Jonboy]

I would swap out the fuel pump relay first with a known good one. If that doesn't get it, pull the fuel feed line and have someone cycle the key. It is supposed to get a prime before the fuel pump relay takes control of the fuel pump. If you are getting fuel, it could be a blockage at the regulator or stuck injectors.

[Evil Trailblazer SS]

Both of my threads below have a lot of good info and wiring diagrams on the fuel system in general, so look through them and see if they get you anywhere...

http://67-72chevytrucks.com/vboard/s...d.php?t=497609

http://67-72chevytrucks.com/vboard/s...d.php?t=500378

[texassquarebodies]

Some tbi trucks have two relays on the passenger side firewall and some have one? Why is that? Whats the other one do? Which is for my fuel pump?

Im tryin to learn up on tbi stuff guys.

[rfmaster]

The fuel pump relay should have a 6" red wire pig tail with flat blade plug at its end. This is a NC (normally closed) terminal of the FP relay contact. You can apply +12 volts from battery (make sure to have an inline fuse). This way you can power up fuel pump and test fuel pressure (9 to 13 PSI at TBI inlet port).
On a subject of fuel pressure - 95% of the time it is either fuel pump dies or the rubber hose that connects FP outlet port to the feed through bursts.

If you can hear the pump then hose is more than likely has bursted. Replace both.

//RF

[foamypirate]

Originally Posted by texassquarebodies

Some tbi trucks have two relays on the passenger side firewall and some have one? Why is that? Whats the other one do? Which is for my fuel pump?

Im tryin to learn up on tbi stuff guys.

Second relay is for TH400 trucks, it's triggered by the ECU for passing gear kickdown.

Also, a bad fuel pump relay wouldn't keep the pump from running. The oil pressure switch will provide backup power once it sees oil pressure in case of fuel pump relay failure.

[bulldog2513]

all the above are good answers and pertinent information but remember the old acronym "K.I.S.S. (keep it simple stupid)? check your fuel filter FIRST then go to more complex issues. if the filter is clogged you will get no fuel delivery. just a thought.

[texassquarebodies]

You boys are smart!!! Here what I have done to it today. I bought a new fuel pump relay, still no fuel. I undid both fuel lines, no fuel comes out. I hear the fuel pump priming. I think I changed the fuel filter before, but thats my next thing to do before fuel pump. Its has been sitting for probably 5 years.

[beamn7]

Originally Posted by foamypirate

Second relay is for TH400 trucks, it's triggered by the ECU for passing gear kickdown.

Also, a bad fuel pump relay wouldn't keep the pump from running. The oil pressure switch will provide backup power once it sees oil pressure in case of fuel pump relay failure.

This brings up a good point, the oil pressure sending unit is part of the circuit.
Fixed a 90 Suburban 454 once with a faulty connection at the oil pressure sender causing fuel pump to cut out intermittently. GM has been doing this for years, even pre-fuel injection. Low oil pressure would interupt circuit to HEI module (pre EFI) and kill the engine. (not all models)
Picked up a early 80's mini blazer with a 2.8L once for $200. Guy couldn't get it to run. After paying him, poured a quart and a half in it, fired up and drove home....

Reason for doing this on a FI vehicle is in case of an accident, engine quits and fuel pump does not keep running. Ford went with an enertia switch..

May want to check the sender, the connection at the sender and the oil level....

Best of luck.

[Jonboy]

The pump may try to prime but still not put out enough pressure to run. If the filter doesn't do it, I would look at a pump. If you aren't in a huge hurry, I will be pulling the TBI pump out of my '74. You are welcome to it, but that won't happen for a few weeks. It's too hot.