Ron-
James sent me a bunch of pages of wiring diagrams from his FSM, and I
got a good look at the schematics except for 1 page that didnt make it
through to me. I'll try not to go too far too quickly, we'll start with
easy stuff, but after that you'll at least need a copy of the pcm
connector grid and circuits so you know which pin goes where, etc, and a
good working knowledge of the parts on your truck and a voltmeter and
ohmmeter. I apologize if I mention something that someone else has
suggested. I tried to follow the thread closely, but I am on digest
version and I may have missed something. Read my whole post, then go
back and read it again and things should gel a little better.
First off, let's start with easy stuff.
I am assuming that you have a good battery that cranks the engine
well, and that the battery connections are nice and clean and tight. If
the battery voltage is not up to snuff, start there.
Assuming it's good: I cannot find any mention anywhere that you
checked for codes and the computer is clear of them. If you havent
checked for codes, you should not need a scanner if you truck is a '95
or older. Pull codes and tell me what you get. A code 55 denotes end
of sequence.
If there are codes, that's where we need to start, and will simplify
this a bunch. If there are no codes, here's what you gotta do:
Your computer (pcm) takes all the inputs and decides that it's time to
make the engine run and powers up or grounds out all the circuits
required to do so. So you need to make sure the computer has the power
going in to it that it needs to turn on, and supply circuit feeds. It
also has to have a good ground to ground out stuff like the injector
circuits, etc. So, did you check every possible fuse, including every
fuse box/panel/distribution center under the hood and under the dash.
Check 'em all again just to be on the safe side.
After you've checked the fuses and checked for codes and there are
none there, you can do a quick test on the asd relay and fuel pump just
by turning the key on. I cant tell what the asd relay controls because
it goes to the page I'm missing, but pin 51 should turn hot when
cranking, and possibly when the key is just turned on cause that goes to
the powered side of the asd and fuel pump relay. The schematic is poor
at the asd section, and I cant tell whether the asd relay in turn powers
the fuel pump relay, but I can tell that pin D of the fuel pump relay
should turn hot when you turn the key on and you should be able to hear
the pump energize for a second and make a buzz noise. If you hear the
fuel pump buzz just by turning the key on, then I would assume that the
asd and fuel pump relays are receiving power and are functioning
normally. If you dont hear a buzz, then you need to see if they are not
getting power because the computer is not getting power, or because the
computer is bad and not giving them power. So, if you got a buzzing
noise, you should have voltage to the coil, because the computer circuit
that powers the relay also supplies voltage to the coil. If you have
voltage at the asd but not the coil, you probably have a broken wire
somewhere between...With the computer hooked up, the circuit that feeds
pin D on the ASD relay also feeds voltage to the coil and injectors. If
you have voltage at that pin then you should have it at the coil.
However, I know you said the coil had no voltage. Check the orange
wires to the injectors, they should have voltage with the key on. The
computer grounds the coil and the injectors to make them function, but
that is done with solid state circuitry inside the computer and the only
thing you can try to do to test that is to ground pin 19, but it
probably wont do any good since you have no voltage at the coil anyway.
If you have no power to the ASD relay, and you dont hear the fuel pump
energize, then you need to get into the deep stuff by checking voltage
and ground on the pcm (computer). You may want to unplug the computer
(after you disconnected the battery) to check the feeds and grounds, I'd
hate for you to fry the computer if it is good. Hook the battery cables
back up after you disconneted the computer connector, turn the ignition
key to on, and check the voltage at pin 3 and 9. You should have
battery voltage from there to ground. Switch to ohmmeter, and check for
continuity to ground from the case of the pcm, then unhook the battery,
plug the computer back in, and rehook the battery up, and check pins 11
and 12 for continuity to ground. For giggles, you can also check for
continuity to battery positive, but you might want to unhook the
computer first. Sometimes you can get a short to ground, and you will
get conflicting readings so it's always good to check a couple things.
Check pin 57 for battery voltage, that supplies the asd relay and the
coil as I said earlier. You will probably find a circuit that is not
powered. The only other way that may happen would be if you pulled a
code earlier, and found a problem in a sensor such as the crank or cam
sensor, whether it's a bad sensor or bad circuit. The computer has an 8
volt input to both of these, so check at pin 7 for 8 volt input. Other
sensors such as the map and tps have a 5 volt supply at pin 6. Checking
the sensors is a whole separate issue, but the basic idea is that you
are looking for a fluctuating reading from 0 then 8 volts then 0 and so
on, and it should generate a square waveform if you know what I mean.
If a sensor doesnt return a reading as such, then the sensor is bad or
the input voltage is wrong or missing, or there is a bad ground.
To sum up what I said:
Check for codes 1st and let us know what you find.
If there are no codes, turn key on to check ASD relay and fuel pump
relay by listening for the fuel pump to buzz as it energizes.
If you have no buzz there, check the pins on the relays for voltage,
and check for voltage at the pins supplying the circuites on the pcm (51
and 57) If none there, go back and check the power supplies and grounds
on the computer, then lastly look for bad sensor circuits.
I think you will find the problem somewhere in here. This should kill
anywhere from 1/2 hour to 3 hours depending on your skills, so get back
to us, and I hope this helps somewhere.
Patrick
ps. James can supply you with page 8 with the computer pin diagram, or
any other diagram you want. Thanks to James for sending them all to me.
This archive was generated by hypermail 2b29 : Fri Feb 06 2004 - 11:46:36 EST