On Tue, 28 Feb 2012 21:25:33 -0600, Ignoramus14054
wrote:

On 2012-02-29, Larry Jaques wrote:
On Tue, 28 Feb 2012 19:29:17 -0600, Ignoramus14054
wrote:


"Ignoramus10095" wrote in message
I have a Chevy Kodiak dump truck that I am trying to fix.
Pictures of the truck and carburetor are he
http://igor.chudov.com/tmp/Chevy-Kodiak/
Onboard computer bad ?
Check fuel line pressure ?

Looks like throttle body injection (TBI), lots of stuff to go wrong.


Tom, and others, I took some time off this problem, and also took some
time to work on it and diagnose it properly.

Yes, this is based on TBI (throttle body injection).

We replaced the fuel pump, at least some fuel filters, and injector
bodies.

It did not help. Even with new injector bodies, the fuel would, at
best, drip from the injectors. drip, drip, drip

Then I decided to NOT take shortcuts and diagnose things properly,
using proper troubleshooting techniques, organize my workplace etc.

As you know, before the injector bodies, there is a pressure
regulator. It has a spring inside. For testing purposes, I removed the
spring, essentially disabling pressure regulation.

We cranked the engine again, again to the same result. Dripping, not
enough fuel.

Then I measured the voltage supplied to injector bodies, it sort of
varied, but would hover around 2 volts. It seemed low.

Then, I took out the wires coming from the engine, plugged in my
little alligator clips, and supplied 4 volts to the injector body,
using my DC power supply.

Voila, the fuel came out in some force (but not as a shower), the
engine would start and run fine.

I put the regulator back in and, guess what, no fuel again,
even with 4 volts applied to injector bodies.

I ended my experiment right there and went home to think.

Clearly, without the pressure regulator (at full supplied fuel line
pressure), and with more volts supplied to injector bodies, the engine
runs. But what des it mean?

My current thinking is that I seemingly have two problems

1) Lack of fuel pressure
2) Lack of voltage supplied to the TBI.

I have a feeling that both items are a manifestation of the same
problem, which is lack of voltage in the fuel subsystem. I think that
both the fuel pump is not getting enough volts (so not enough fuel
pressure), and also, the injectors are not getting enough volts (so
they do not open properly).

Makes sense?

If so, what could it be? Bad ground?

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.


Larry, what sort of manual would you suggest?

The Chevrolet Truck service manual, Ig. Maybe eBay?
http://www.ebay.com/sch/i.html?_nkw=...+repair+manual

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)
http://www.mitchell1.com/M1Products/...uck/index.html

There's apparently some service recall on diesel injectors.
http://tinyurl.com/7xw8s9e

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