Originally Posted by Pliant

If your pressure regulator is not working you would have no way of knowing

Originally Posted by SB

2nd one sounds more pomising...I said sounds.

The 87-93 truck 7.4L injectors ae the 75-85 lb/hr at 13psi, Neve used at higher psi's. The 94-95 7.4L trucks had the 30psi fuel system with a different injector...which sounds like MErc used in there TBI's and in which I wonder if are the same Volvo used but with diffeent stamping #.

Originally Posted by nunnink23

Hello all. I have a 2000 VP 5.7GSI TBI injected motor which had an oil pan issue last fall. The engine ran great all year, but I pulled the motor to do an oil pan over the winter. Along with the oil pan I replaced a few other items, had the valves lapped, stem seals replaces, replaced the oil pump, injectors rebuilt, and I rebuilt the TBI.

4 weeks ago I dropped the engine back in, buttoned everything up, and she wouldn't start. I went through the normal tests. First verified that I had spark, which I do. Second I verified that the injectors were spraying, which they were. Third I verified compression - 175 PSI Max at all cylinders, 90 PSI first bump. At this point I decided to pour a little fuel in the intake to see if the problem was fuel related. The engine fired up immediately, ran for 3-5 seconds until it started starving for fuel and slowly cut out.

Knowing this must be a fuel problem, I did the following items: BTW - I have a native MEFI III motor, but with a MEFI IV computer and conversion harness, since it died three years ago in the previous owners hands.

1. Verified fuel pressure - 6PSI low pressure pump, 30 PSI high pressure, measured at the TBI.
2. Verified fuel volume just in case - will fill up a coffee can in 2 seconds.
3. Sent my injectors BACK out to an independent shop to be flow tested again, just to be sure the first place didn't make a mistake. They checked out fine.
4. Rebuilt the TBI AGAIN, just to make sure I didn't tear the diaphragm the first time. I don't think I would get a proper fuel pressure reading without a working diaphragm, but just to be sure I did.

Nothing changed at this stage, so then I figured my problem was electrical.

I pulled the codes, and I had a myriad of them, but all were due to me cranking with items such as the MAP or TPS disconnected trying to override a faulty sensor if that was causing it not to run. I tried disconnecting the S.L.O.W sensors, and this made no difference.

My marina suggested that even though my injectors were spraying, and pulsing, that I should put a NOID light on it. I did this, and it flashed rapidly. I don't know how bright they typically flash, but mine seemed a bit dim, so then I figured my problem was voltage or ground from the injectors. I checked the following items at this point:

5. Verified that my injectors had B+ voltage at the hot lead (with a multimeter). The battery had 12.58 V, injectors 12.47 V.
6. Traced the injector ground wires back to the J1/J2 connectors and checked for continuity, then traced the same wires through my MEFI IV conversion harness, and also had continuity.
7. Traced and checked all the ignition module wires back to the ECM and checked for continuity.
8. Traced all four MEFI IV ground pins to the ground wire, and checked for continuity.
9. Checked both my engine post grounds for abnormal resistance.

After getting this far, I decided my injector drivers must have died in the ECM. I sent my ECM to OBD Diagnostics to be bench tested. He called me two days later and said the unit was fine.

After getting my ECM back, I replaced the ignition module, and coil - not sure why, but somebody at my marina suggested I do this since he had a similar problem and it turned out to be these. No change in my condition after replacing both.

Now I do not know where else to turn. I apparently have a good ECM, new ignition module and coil, good spark, good compression, good injectors, good fuel pressure, and yet my engine wont start. If I let it sit all night, it usually will sneeze on the first few cranks of the day, but that is all. As it was before, if I pour fuel down the intake, she will start up and run until it starves for fuel. The engine has set codes before, but as I said they will never come back unless I disconnect a sensor or connector, so there are no hard faults.

I am getting a bit desperate at this point, since even my local mechanics are confused. I am considering buying a SBC TBI off a GM truck locally just to try to start my engine, and if it runs then I know my TBI is bad SOMEHOW, even though the injectors have been tested twice, and TBI rebuilt twice. For whats its worth, I don't know what injector post resistance is supposed to be, but mine is 1.5 OHMS.

Should I just by the Diacom tool and start reading sensors? Or should I pull my harness out of the boat, unwrap it and trace every single wire/check it for continuity? I also ordered a new MAP sensor just because I want to rule it out - even though I am told disconnecting it will set the ECM in a default that should allow it to run, and this didn't change my condition.

Any help would be greatly appreciated. If anyone needs a diagram drawn of the MEFI III to IV conversion harness I can do that.



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Originally Posted by offshore312

I've been following your thread, and can't help but wonder if one of the "few items" you replaced (when you did the oil pan) the timing chain and gear sets?

Originally Posted by SB

He's got 30psi. So the reg must be working.