NEW RESULTS was Chevy Kodiak dumptruck gasoline problems

Yes, that's possible. But electronic ignition systems and EFI are computer controlled. Unless they get all their ducks in a row, things don't work properly. Get the manual, get the test equipment and let us know what you find. Or have a tech drop by with same and let you know.

-- ...in order that a man may be happy, it is necessary that he should not only be capable of his work, but a good judge of his work. -- John Ruskin

Bad grounds could certainly do it. The pressure regulator may be ok, but the fuel pump may have a low voltage condition as well and not be keeping up the appropriate flow.

Possibly the wrong fuel pump. I would expect this TBI needs something close to 50 PSI at the minimum.

Maybe not. The computer probably sends short pulse-width modulated pulses of 12 V to the injectors. If the starter isn't too noisy, you should be able to hear it clicking when you crank. You can definitely hear the injectors on most injection systems (but maybe not with the starter running).

Maybe, should be relatively easy to check. Yes, could be a bad ground. The fuel pump is probably not controlled by much electronics. There may be a fuel pump cutoff relay, but that usually is on cars with airbags. But, I'd measure the fuel pump pressure. Somewhere there ought to be a spec on fuel pump pressure. A quick test just with a gauge connected to the pump would tell you whether you are getting 10 PSI (carb pump) or 50 PSI (FI pump).

The injectors may be working perfectly, but with no fuel pressure, the computer is applying short pulses that SHOULD be right at the higher pressure.

Also, since the pressure regulator made a difference, it may show that the regulator has a ripped diphragm, crud under the seat or some other malfunction. Actually, a typical regulator would set lower pressure without the spring. But, this one might not be typical.

Jon

Yes. The pressure regulator looks OK, in fact, there is not much that could go wrong with it, and it looks like there is nothing wrong with it.

i

Pete, what sort of a manual would you recommend, I can shell out some $$$, not only to save money on repairs, but to learn something.

Repair manual or what is it called?

i

Larry, what sort of manual would you suggest?

The Chevrolet Truck service manual, Ig. Maybe eBay?

The dealership are way too damned proud of their manuals, wanting several hundred dollars for them.

Second choice would be a Mitchell manual for the truck. We used them for all repair work when I was a mechanic at non-dealer sites. They're great! (Not cheap.) Try this link. (unknown to me)

There's apparently some service recall on diesel injectors. G'luck!

-- ...in order that a man may be happy, it is necessary that he should not only be capable of his work, but a good judge of his work. -- John Ruskin

In the old days, they were called Factory Service Manuals. YMMV

-- ...in order that a man may be happy, it is necessary that he should not only be capable of his work, but a good judge of his work. -- John Ruskin

I downloaded one from here last week:

I was dubious about the site but all went well, G'luck!

You say 2 volts and 4 volts. This does not compute. WITH THE INJECTORS DISCONNECTED what voltage do you have on one side of the injector with the key turned on? It SHOULD be roughly 12 volts from terminal to ground. When the computer triggers the injector, the computer GROUNDS the injector for a short time. Measuring across the injector will give you a low voltage that varies with fuel requirement. A bad ground on the computer will cause a low voltage drop across the injector which translates to low injector current and reduced injector opening. The same will happen with high resistance in the power supply circuit. The voltage on the "feed " side of the injector should remain at 12 volts even when cranking (well, it WILL drop some - but it should remain "battery voltage"). If it drops below battery cranking vultage you have a bad connection somewhere in the power feed circuit.

To test the fuel pressure regulator pinch the rubber return line and see what happens to the pressure. Those regulators have a bad reputation, for a good reason. Note - the RETURN line, not the feed or the vacuum signal line. The injection pressure is regulated to provide the same pressure drop across the injector under WOT (low vac, or high manifold absolute pressure) as under low throttle (high vac, or low manifold absolute pressure) so a given period of injector opening provides the same amount of fuel regardless of engine fuel demand.

Also take a look here for the manual/s:

IIRC, depending on vehicle, they have original factory shop manuals (FSM), reproduced FSM's and the ones like the DIY parts stores carry. For some vehicles they even carry factory assembly, parts and owners manuals.

I've only had one personal experience with them and it was positive. Have some friends who speak highly of them too.

As the above poster mentioned, Mitchell manuals rock too.

And a question: is fuel leaking 'through' and dripping off your injector/s, or somewhere else and just running down and off your injector/s

In a nutshell, remember most (if not all) injectors are energized on one lead anytime the key is on, and controlled via the ground side through the computer. Needless to say, a good computers ground is very important.

Erik

On 2/28/2012 10:14 PM, Larry Jaques wrote: ...

No bearing on TBI system on a gas engine, though...

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If it's close enough to be of use, I could send you my old 1990 R,V,P,G series service manual. It's far too big to scan all of it, but it would fit in a PMFRB ok.

You can get NOID lights on loan from many auto parts places (with deposit), and the injectors are usually driven on the low side.

Two sources of power to the fuel pump, one if the fuel pump relay controlled by the PCM and the second is an oil pressure switch.

According to the doc, the old TBI systems are supposed to run 9-13 PSI, quite a bit less than the later MPFI systems. A FI pressure tester is about $20 at the auto parts place.

Where do they plug in?

That would be awesome, I can paypal you for the pmfrb cost.

I was measuring voltage between two terminals going to the injector body, with an averaging voltmeter.

Right.

Which is what a bad ground is, kind of .

Sounds like a good thing to check, voltage on the feed side vs. ground/body potential.

Another great idea, will try to find it.

That vacuum line, I think, is disconnected, may be an issue.

OK, why do the regulators have a bad reputation?

Thanks a lot

i

Just email me a mailing address and I'll see if I can get it shipped off tomorrow.

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