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Old 10-25-2006, 06:44 PM
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1988 chevy Fuel Injection Problem

hi there, I have a 1988 chevy c/k 1500 truck, I just purchased this truck and it does not have any injector pulse. Or fuel going to them. yes i have gas in the tank, I was told that it might be the computer so i switched that, with a good one and it will only fire if i put a bit of fuel down the injectors. The fuel pump is good, If any buddy has had a simalar problem and fixed it please help me out, Or even a wiring diagram or sumthin. thanks alot

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Old 10-25-2006, 07:12 PM
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How do you know that your pump is good? Pull the feed line off of the back of the throttle body and see if it is getting fuel. Have a rag wrapped around it and have a buddy turn the key on. A fuel pump can be weak and not allow enough fuel to get to the throttle body. A fuel injected system runs a lot higher pressure than a standard fuel system. It could also be a fuel filter that is restricting fuel to the engine. It is not in the electrical because you say it will fire if you dump fuel down into the TB, so it has to lie in the fuel system somewhere.

Kevin
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Old 10-25-2006, 07:57 PM
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Doc here,

After you clear the fuel issues, and still believe it may be electrical, Check the fuse box for fuses marked ECM, COMP, INJ, FUEL PUMP.

If that is good, pull an injector plug, and turn the key on, measure the red wire for 12 volts .

If good, using a Noid light ('Or if you have a fast enough time base DVOM ) measure the black or smaller wire while cranking..It should flash as it cranks..If it does the circuit is whole. DO NOT ground this wire..It is NOT a ground! It is a pulsed Low Signal..grounding it will damage the computer buffer/driver.

If you have that, you have Injectors that are servicable..you need to go back to the fuel side and inspect for delivery problems.

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Old 10-25-2006, 10:23 PM
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Quote:
Originally Posted by Kevin45
How do you know that your pump is good? Pull the feed line off of the back of the throttle body and see if it is getting fuel. Have a rag wrapped around it and have a buddy turn the key on. A fuel pump can be weak and not allow enough fuel to get to the throttle body. A fuel injected system runs a lot higher pressure than a standard fuel system. It could also be a fuel filter that is restricting fuel to the engine. It is not in the electrical because you say it will fire if you dump fuel down into the TB, so it has to lie in the fuel system somewhere.

Kevin
Hey thanks, I think there is something in the fuel filter, But when i hook up the noid to the injectors theres still no pulse, so im not getting fuel up there but once i figure that out i still have problems with the injectors
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Old 10-26-2006, 02:57 AM
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Doc here ,

If the Noid light is not working, you have no injector pulse..no matter how much fuel you pump up there it will hit a brick wall at the injector.

The reference pulse going back to the computer from the Distributer may be missing, or the computer may be bad..Or the computer edge card is dirty or not seating properly..inspect and clean.

Have the module checked..it is free and it may be partially failed..

Is this a Full EFI ? or a TBI?

Doc
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Old 10-26-2006, 03:57 PM
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An '88 should be TBI.
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Old 10-26-2006, 04:13 PM
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k, well i guess i'l try switching the computers around, i have about three of them, so one of them should be good
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Old 10-26-2006, 04:44 PM
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1988 fuel injection oroblem

When you turn the ignition key to on the fuel pump should run for 2 seconds. Then shut off. The pressure should be 9-13 psi. Try to do a flow/pressure test and go from there. Once you have fuel look for the injector problems.

Note: when cranking the engine once the oil pressure reaches 4 psi it bypasses the fuel pump relay......russ

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Old 10-26-2006, 04:45 PM
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I gotter

Hey thanks for all your help, i took the fuses out, and some of them had some crap on them, so i just scuffed them clean and fired right up, I guess I'll just get some new fuses. Thanks
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Old 10-26-2006, 05:07 PM
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Doc here,

Check the paper tag on the computers...

Be sure the Numerical and / or Bar code are the same in all three. If not, they MAY NOT interface..on your engine.

Did you Change out the Prom and CalPack? If these are new or Bone Yard.. they usually DO NOT come With the proms installed..you may have blank sockets under the egress Doors..If that is the case, you'll have to use the first computer proms.

These are usually the main Failure point also aside from buffer / drivers, so they may be bad..(you may have to order another one / set)

The PROM, is the PROgramable REad ONly MEMory Instruction set for the micro processor. It instructs the computer how to function..What parameters it has to operate within..and how to react to sensory inputs..The Short Brief "Bare Bones" Analogy of the prom is:

If it, or parts of it are damaged or erased , then the processor can not function withing operating standards..E.G. Signal ref--->Injector opens---->Time--->Injector Closes--->Time--->Combustion...Signal ref---> ECT. If part of the program has a glitch Some part won't work..Like for instance , removing an intake push rod for an example(on a non Computer Vehicle)..you have no fuel induction to the chamber..(or No injector pulse on a Computer controlled engine)

Some program themselves Through ignition Cycles, and have a "Window " of parameters They constantly update and settle into Via sensory input..allowed by EAROMs (Electrically Alterable Read Only Memory's ) Though I doubt an 88 will have one..

Others are factory (or By other's) "Blown" or programmed with a set of instructions that Tell the micro processor how to operate (PROM) and do not change (on their own..) most likely what you have.

These Don't change, They are Thousands to Millions of Data Bits, held in place by a charge at programming, on the PRG pin..once the chip is programmed the "Bits" are sorta of "Electronically or magnetically Clamped" in at their memory location and will remain there until power is applied to that pin (Akin to a Cold reset on your computer..) The result is memory charge "Slips out to ground" and an "Empty Memory" platform..One reason why static Discharges are deadly to computer architecture.

The Net result is the processor sits there with sensory input and thinks ... "You want me to do what?" because it does not know how to respond.

To Change yours, open the egress door, and you'll see one or two 24 or 28 pin chips with a plastic "handle". Be sure your work area is static free .. don't do this on a shag rug on a humid day..and you should get a static grounding wrist strap (rat crap..about $6 bucks)

Ground the strap to the computer case, the Velcro strap goes around your wrist. "Rock or GENTLY pull the chip straight up..Do Not bend the pins..Then remove the chip, Noting the locater or #1 Pin location from the circuit..DO not handle the pins! Install in the new computer socket. Seal up the egress Door, and install in the truck.

Doc
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Old 10-26-2006, 05:14 PM
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Quote:
Originally Posted by 52Ford
Hey thanks for all your help, i took the fuses out, and some of them had some crap on them, so i just scuffed them clean and fired right up, I guess I'll just get some new fuses. Thanks

Doc here,

KEWL, you fixed it while I was responding... Glad it was simple..

Quote:
Originally Posted by docvette
After you clear the fuel issues, and still believe it may be electrical, Check the fuse box for fuses marked ECM, COMP, INJ, FUEL PUMP.
Good to hear it's running, and OTR again!

Doc
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Old 10-26-2006, 05:28 PM
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CHEVROLET
A Division of
CORVETTE

Buick.. a division of GM that shows Corvette's what Tail lights look like

You sound like a experienced tech Doc...

Always good to start simple with the fuse and then work from there. I can't tell you how many time's I've chased my tail and forgotten the rule of FUSE FIRST.. .Lol...
For future referece... if you've got no sparky and no fuel at the same time it's the ign. module under the cap in the Dist.
Glad it's up and running...
~Scott
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