ranched

Hello,

I'm new to this forum. I've recently purchased an 88 pickup and have been studying and learning from this great collection of knowledge. I have searched and tried diagnosing my issues but they have changed since I started trying to fix them.I figured I'd ask for help since I want to learn and fix things as efficiently as possible.

First a little information. Its an 88 pickup efi v6 auto transmission. I was able to drive it home. The previous owner had done some wiring to work around issues instead of fixing them. (I'm assuming this is the case, there's a wire running from the fuses in the cab to a switch which controls the fuel pump) The PO had also pulled the check engine light which was the first thing I fixed. Upon reading the codes, I found that I had codes 25 and 26 and code 52.

Yesterday, I started at the knock sensor from the code 52. The PO had the heads replaced so I thought this might be an easy fix if it was the connection to the engine wiring harness. I took the throttle body off and checked the connection, looked good. reassembled and still got a code 52. I thought, "ok add a pigtail to the shopping list" and continued to the codes 25 and 26. I reconnected everything and the truck started right up, no problem.

Today, I decided that I would try to find whatever was broken that the PO decided to wire around to the fuel pump because I thought finding this might solve my 25 and 26 codes. This is where I started having problems. I checked the main relay, was good. I checked the circuit opening relay, it was good. Then I thought I'd try to start the truck to make sure I could at least return everything to a functional, if not optimal state. The truck would no longer start. It would crank, I could hear the fuel pump running and since it is in this altered wiring condition, I could hear fuel entering the engine compartment constantly while the switch is on. However, I no longer get a check engine light when I initially turn the key in the ignition. I don't know where to go from here.

I was thinking that somehow I accidentally broken something else, (I did forget to take out the jumper after trying to check cel and attempted to start the truck with it in. I don't know if that would have an effect but I'm new to these trucks so I don't know) One thing I thought of after double checking everything was that maybe the efi computer is no longer receiving power and not able to supply the power to the check engine light? Is that a possible explanation?

Any help would be greatly appreciated.

scope103

You might have a slightly leaky injector. Not enough (usually) to flood the engine, but with the fuel pump running continuously for awhile, might have flooded it. Try again, then remove the plugs and look. Wet suggests too much fuel, or the right amount of fuel and no spark. Use a timing light on each plug wire to confirm that each plug is firing. Dry suggests no fuel. Since you're sure the pump is running, you can put a mechanics stethoscope on each injector to listen for the clicking. Or a "noid" light to check for injector signal.

I'll wager you have a bad VAF; part of the function of the VAF is hold the fuel pump "on" when you release the key. If the PO wired around that section, the metering section could also be bad (that would easily lead to codes 25 and 26, at the same time). The procedure in the '93 manual will probably still work for you. http://personal.utulsa.edu/~nathan-b...92volumeai.pdf

I hope you got a good deal. When someone "fixes" the truck by pulling the CEL bulb, you know they just don't care. Good luck!

ranched

Ok, thanks! I'll try that in the next few days and update afterwards.

ranched

The tuck is running again. I discovered that i had blown the EFI fuse. After replacing it the truck started right up again. (I don't know how this happened but I would like to try to not repeat it. Anyone with any ideas?) I continued searching for the cause of the code 25 and code 26. I checked the VAF like you suggested scope103 but all the readings from the terminals were within spec. I started testing continity in the wiring from the fuel pump back upstream. I checked from the blue wire in the pump harness back to the COR and that was good. I checked from the COR to the main relay and that was good. Is there something I'm missing? If that wiring is good and the COR and the main relay are both good(I think. I've tested each a few times now) then what else could be causing the pump to not get power when trying to start the truck?

scope103

Did you check the COR itself? http://personal.utulsa.edu/~nathan-b...38circuito.pdf

With key-on, if you push the vane in the VAF, the COR should close.

The COR has two coil windings; one powered by the STA signal (when you turn the key to start), the other powered from the VAF (once the engine starts sucking air, this will hold the pump on after you release the key). It's a little harder to check the STA signal (because the noise of the starter will drown out the sound of the COR closing.)

Why do you care? If you're in an accident that breaks a fuel line, your pump will keep spraying gasoline until you can reach the switch to turn it off. That's not a chance you want to take.

Inspect the wire connection to your O2 Sensor. Some have reported that a short to ground (getting the sensor wire too close to the exhaust, melt through the insulation, get an intermittent short) will blow the EFI fuse.

ranched

I took the COR out and tested it although not under load. I did hear it clicking when trying to start the truck. I'll check it tomorrow under load after I get some test leads. I'll also check the o2 sensor wire for shorts. Thanks for your help so far.