93 3.0 no start when hot

[jarmo]

My 93 3.0, 5 sp, 4x4 wont start when its hot. starts when cold, but runs like crap for about 10 secs, then revs to about 2500 rpm, settles down and idles fine. If I drive it, it runs great till it gets hot. then it starts missing, spuddering, and acting like it dont want to go, especially at low rpms. If I keep it down a gear, and rpm up, its fine. If I shut it down, forget it, no start. Pulled codes 121, 411,538,&543, so I replaced the tps, no improvement. Any ideas? I know 543 is the fuel pump secondary circuit open pcm to battery. Just dont know what to check.

 

[RonD]

543 means fuel pump relay should be closed and isn't.
Secondary circuit is the power for the fuel pump.
Primary circuit is the coil in the relay, it gets power when key is turned on but doesn't close.

Fuel pump relay is controlled by the computer, computer Grounds this relay to close it, prior to Grounding it that pin/line would have 12volts on it from key being on.
When relay is closed it sends the 30amp power from the Fuel Pump fuse to the Inertia switch and from there to the fuel pump in the tank.

In between fuel pump relay and inertia switch the wire is spliced, this spliced wire goes to the computer.
This splice can be at the fuel pump relay or on inertia switch.

Computer can then monitor the 12volts on the fuel pump's power wire.
543 means computer is Grounding Fuel pump relay but is not "seeing" that power on the spliced wire.

Usually indicates faulty fuel pump relay.
They are not expensive, $5-$9, so almost worthwhile to replace it, and if that doesn't solve the problem then get out the volt meter and start testing wires.

 

[jarmo]

will absolutley replace relay. This truck has been totally reliable, and really want it back on the road. Thanks Ron, will update as soon as I change it out.

 

[jarmo]

Ok, replaced relay and got same thing. Do you think it might be maf, or in the distributor? Recently replaced plugs wires cap rotor and coil. Maybe the pickup in the distributor. I noticed it has a orange spark when it's hot and won't start.

 

[RonD]

'93 3.0l is using TFI spark system, TFI modules do start failing with age, usually noticed after engine(TFI module) warms up.

Good read here on that: http://www.therangerstation.com/tech_library/TFI_Diagnostic.shtml

Pickup in distributor is a Hall Effect sensor, they are not a common failure, TFI module or it's wiring is more likely

 

[jarmo]

Is the that the one located on the core support? I forgot about that and had to replace it when I got the truck bout 8 years ago.

 

[enjr44]

https://www.google.com/search?q=93+...=0ZvQVuueFYP0jwO5oY24BQ#imgrc=amF07yR4k_aoAM:

 

[jarmo]

ok, took the tfi to auto zone, it passed. guy there told me iac valve. does that make sense.

 

[RonD]

ok, took the tfi to auto zone, it passed. guy there told me iac valve. does that make sense.

No, not IAC valve, but you should clean it now and then, every 2 or 3 years

You said, "wont start when its hot. starts when cold", and I would have to assume AutoZone checked TFI module when it was cold........................

You are chasing down an intermittent issue, since it does run OK at some times.

 

[jarmo]

That is correct Ron. The truck was not run at all for about 24 hours. When he tested it and it passed, I asked him to check again. On the second time it passed, he said it was getting warm. I said give 'er hell. Total of 10 tests. and pretty warm when handed to me, it still passed. He asked me what was up with the truck, and I told him. He said he had similar issue with one, and it was iac. Just wanted another opinion.

 

[Curious Hound]

Please forgive my ignorance. I'm just reading this thread to put info in my head in case I need it later on.

What is tfi?
what is iac?

Thanks.

 

[jarmo]

Thick Film Ignition. Basically the ignition module thats known for hard to troublshoot issues.
Idle Air Control valve, bolted to top of throttle body.