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Old Iron

Well-known member
Joined
May 19, 2011
Messages
15,254
Location
Willard Mo.
I put a 48 AD 5 window on a S10 with the 4.3 tbi
Cleaned out the fuel tank and installed a new fuel pump.
I hooked the wire harness to the engine and ran it through the firewall. The PO butchered the interior harness.
I turned the key, lo and behold it started and ran good. Turned the key off several times to make sure it would start and run.
Turned the engine off and went in side the cab to clean up the wiring and one of the wires shorted on the floorboard, blew a fuse so, I replaced the fuse and now the engine won't fire unless I prime the tbi with gas. All the other fuses are good. The fuel pump runs.
Engine runs perfect after it starts but, will not start after turning off the key without priming again.
When I turn the engine over the injectors blip a small amount of fuel at first then, no more fuel comes out will trying to start.
I could use some wisdom from you guys :confused:
 
If that system is like the TPI on my Vette, the computer will turn on the fuel pump relay for something like 5 seconds on starting, then the oil pressure sender sends a signal to the relay when oil pressure gets above 15psi {I think}, and as long as there is oil pressure, the pump will run. Sounds as if the relay is not getting the signal from the computer to turn on and pressurize the rail, or the relay isn't connecting somehow. Have you tried straight wiring the pump to run all the time the switch is on to see if it will crank then?
 
Try unplugging the MAP sensor, just the electrical, not the vacuum and give 'er a spin.

I couldn't find a photo online, so I shot the TBI 4.3 I have lying on the floor... the sensor is boxed and the plug is on the inboard side (arrow).

attachment.php


It's possible, the sensor "thinks" the engine is running and therefore gives no signal to enrichen/prime/start.

I suspect you have no input voltage or have cooked the sensor, but that may be coincidence, or not your problem at all!

You can test the sensor either on the vehicle or on the bench with a voltmeter and a vacuum pump... or enlist the services of a good sucker. [ddd

http://troubleshootmyvehicle.com/gm/4.3L-5.0L-5.7L/how-to-test-the-map-sensor-2

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OK here's what I've done.
Went to the big O and got an ignition module, installed it and it took a couple tries and it started.
Turned it off and it starts every time now.
If it decides not to start I will try the MAP sensor.
Thanks for the help!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!![cl :cool:
 
I've heard of "half-baked" modules, but haven't had that experience myself... yet.

Anyhow, I'm glad you got it going! Treat yourself to a cold drink and a carbureted burnout!

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I was right.
The problem is still the same.
Initial crank sends one to two squirts of fuel then nothing.
Doc I tried the MAP unplug it resulted in the same.
 
I've done some more thinkin' and readin'...

You might have voltage drop while cranking. Unplug an injector and test the plug... IGN switch on, cranking and released to run. The drop, from on to cranking should be very small and the minimum is 9 volts at the injector. (I have had this problem, where the IGN switch is weak... cranks all day... but doesn't deliver proper voltage to other circuits.)

If the voltage is good and the injectors are operating properly (which I believe has been proven when it runs) you likely have a delivery problem... low voltage to the pump, low fuel pressure or restriction.

My theory is, you have an almost operating system, short on supply. I hope that makes sense...

.

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Not yet.
Gonna try a temp sending unit.
Wire harness.
Then a computer.
I think the major problem is the interior wire harness has been butchered before I got it.
 

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