DBRjeep350TPI

This is my problem. I have a TPI 5.7L and it starts great cold and warms up to closed loop fine. I take it for a drive and no problems at all driving. But when I turn it off and try to restart it within 5-20 minutes it won’t fire up… It does not do it every time, just occasionally. The last time it happened I had to prime the rail 2-3 times and then crank it and it would start briefly and die. I repeated the priming several times and it fired and died multiple times…. Then I all of a sudden it fired and ran!!! I drove it 5 miles and turned it off and waited 10 minutes and cranked it and it fired up and ran fine. I have no clue what is going on. I had one person think that it might be the fuel pump not supplying consistent and continuous pressure.
The engine has been rebuilt and all new sensors and computer/memcal. I have updated the ignition system with new plugs, ignition control module, cap and rotor, plug wires, etc… I have also replace injectors with bosch design III, new fuel filter, new adjustable fuel pressure regulator set to 43psi. I have no ERG on the system.
I am stumped and help would be awesome.

skibum2100

Does your car have VATS? When this happens does the "security" dash indicator light, light up?

What do you mean when you say prime the rail? Do you mean turn the key to "run" and then try to start it? Not temporarily twist two wires together?

When the car starts "briefly and dies," how does it run (normal or not)?

What is the fuel pressure during the problem? (tape a gauge to your windshield until the next time this happens)

Are there any trouble codes?

Hope this helps.

edit: I just read your username, I suppose this is in a Jeep...

DBRjeep350TPI

You are correct this is in a jeep, but I wanted the heart of a Chevy!!! The car does not have VATS the chip is a hypertech thermo cal II. there are no trouble codes that trip when it does this at all. I have not put the fuel gage on and ran it to see what it does when it has it’s little misshapes... but will do and route it up to see it in the cab.
When I say prime it... i will turn the key to start, then back to off for 5 seconds and prime again listening for the fuel pump and then again a third time, then it will start up roaring like a champ "Normal I would say" for a few seconds then sputter like it runs out of fuel and dies. I did this a few times and the same effect each time (even throttling it a bit), then all of a sudden it fired up and ran with no problems.

BuzzLOL

.. Sounds like the oil pressure switch that turns the fuel pump on for continuous running may be going bad... I assume the engine is full of oil...

vetteoz

iTrader: (13)

Nothing to do with it unless the pump relay also faulty
and OP states pump primes so obviously that is working as it should.
OP switch supplies power to fuel pump if pump relay fails , with normal operation nothing to do with start up

If engine cranks over it ain't VATS

vetteoz

iTrader: (13)

Only way you will determine if a fuel supply ( pressure ) problem or a fuel control (electronic ) problem

DBRjeep350TPI

The engine is full of oil and hold good oil pressure (40Psig), so you guys think that it might be the fuel pump relay? Do you think that that the fuel pump may be cutting out? the Fuel pump is OEM jeep wrangler for a jeep FI system... Others have used it on TPI 350 and claim that the fuel pump from a jeep works. But I am skeptical that it may not be enough or also it is 18 years old...

rgarcia63

The oil pressure switch is in parallel with the fuel pump relay as was said.
An extended crank time will be experienced when the fuel pump relay fails because no power will get to the fuel pump until there is enough oil pressure to close the switch.

Remove all doubts about jeep pump, use a pressure gauge.

DBRjeep350TPI

I think that i might just replace the oil pump switch and see "it’s cheap enough to try". I will hook up the gauge and see what the fuel pressure is doing when it does do its hiccup...
Thanks for all the good comments guys!!!
I appreciate it.

EagleMark

That would be true in original car. But this is a transplant/conversion so I doubt he used the VATS/PassKey module with starter relay.

You can pass the replacing oil switch and go directly to diagnosing fuel pressure. It will tell if it's a relay issue or oil pressure sending issue.

VATS must be disabled in chip or one of those vats things wired inline already or it would never run.

I had a weird hot start issue once but it was TBI. Had a flapper in exhaust pipe to force hot air through engine/intake when cold. When it warms up it is supposed to open! Mine was stuck so intake was always getting heat, very hot and at warmed up restart the fuel would just vaporize like vapor lock and when it was finally running it was flooded and had to clear it out. So if you have this heat riser valve on exhaust manifold make sure it is free to open and close.

DBRjeep350TPI

I was curious if my fuel might be vaporizing in the fuel line causing the vapor lock condition... the flapper your talking about is it stock? I have a mega muffler and all new SS pipe with no CAT and headman headers. so it is pretty free flowing...
I ran new fuel lines to the rail and they are away from the exhaust pipe, but will recheck. I did do the mod to the fuel rail to have the fuel enter in the 9th injector port and return also with SS braided line back to the tank.

DBRjeep350TPI

i looked at a few picture of this "heat riser valve on exhaust manifold" and I do not have one on my system... is there any other ways that my fuel might be vaporizing?

skibum2100

Yes, the fuel rail (on my f'body) can reach 154F and my car vapor locks when the outside of my metal gas tank reaches ~120F. If you don't have enough air flow through the engine compartment there is a chance of overheating the fuel. This is a RIDICULOUS problem that many of us have been chasing, but it mainly shows up during the summer (when temps are hotter).

Good luck...

DBRjeep350TPI

I am wondering if that could be my problem. lately here in Oregon the temps have been around 40 degrees F. But may still be vaporizing the fuel. I have a question if the fuel is vaporizing in my rail/line will the pressure gauge hooked up to the rail still show pressure (40-45PSI) if it is vaporizing the fuel? Pressure as a gas, not as a liquid? Also if it is a cure would be louvering the hood? I might just take the hood off and run it and see what happens...

EagleMark

At 40 degrees it's probably not a vapor lock issue unless you have the fuel feed line touching exhaust.

I would start looking at other issues...

DBRjeep350TPI

i will give it a good look over this weekend and let everyone know monday!!!
thanks guys

rgarcia63

Fuel systems that dead head at the engine i.e., cam driven fuel pumps with no return can an do suffer from vapor lock at high ambient temperatures.
Fuel Injection systems require high pressurization, the pressure range is maintained by returning unused fuel to the gas tank where the fuel pump is submerged in the fuel making it almost impossible for the recirculating fuel in the lines to vaporize.

EagleMark

Exactly! Almost impossible and highly unlikely in a car unless it had a fuel feed line running to close to or touching an exhaust pipe. Which would not happen in a factory system but could happen in a conversion, but this poster assured us he ran the lines correctly.

But some GM trucks came with a fuel module that would run fuel pump for 30 seconds after shut down to cool TBI just because of the possability. Trucks run harder and hotter then a car. It is seen in the attached 7747 wiring diagram.