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Code Reading Q's

If you want to clear the ECM, just pull the ECM fuse for 10 seconds. A lot easier and does the same thing. Just FYI for the future.

I believe the ECM grounds the dash bulb, the light should be on with the key in the run position, with the engine off. You'll probably have to test that circuit for ground at the instrument panel connector, although if careful, you can remove the ECM connector locking piece (blue plastic on mine) that locks the wires in place. Once that piece is out, you can likely stick a paperclip in the ECM driver terminal, and test for ground off of it. You've got to be VERY careful doing it this way, bust that wire/connector and you have some problems.

You could unplug the IAC and see if the noise goes away, IIRC that will sometimes make noise when you are code reading.
 
You may want to double check that your code reader is compatible with OBD I as well. Some only talk to OBD II and up.
 
The OBD II paper clips are in the RED box at Staples. The ones in the BLUE box are OBD I only. :D


I was referring to his scanner of course. :deal: :waytogo:
 
I agree with Thumder, I think you have a grounding issue somewhere or a bad ECM. The fact that you need 30psi to turn on the fuel pump is very bizarre, that should come on with the key first turned to run, which makes me lean toward a ground issue somewhere. But...the ses light should also come on for it's test when you first turn the key also. It not coming on could point to a failing ecm.

How does the truck run? Smooth at idle? When the CEL comes on, does the truck perform differently?

If you have an ohm meter ($10 USD at Walmart), disconnect your negative battery terminal and your ecm, and check the resistance between the ground at the ecm connector and the negative bat cable. It should be a low number, if it's high or squirrelly, you have a loose or corroded connection somewhere.
 
Once the truck starts, it runs like a top. Nice and quiet (but it also has a new exhaust system). It never shudders, sputters, or resists acceleration.

Well actually it does shudder the the tranny is in OD, and on the service road. But I am also running 4.10's and 35" tires, so i figure it's just under heavy load, and/or bad engine mounts.

When the CEL does come on, the engine performance doesn't change. It usually comes on at a higher speed (80 km/h and up). But I think once or twice it came on when I was go 50 km/h. So speed doesn't seem to matter.

The reader is infact and OBDI reader. I made sure of that. and my truck has the the 12 pin connector (or whatever count it is supposed to be, I know it's not the 16 pin connector)

I just came home with a multi meter and I want to go trouble shooting. So which wire is the ground wire on the ECM?? I disconnected those clips last saturday. They came off really nicely.

So I would just disconnect the harness, and poke (not stab) one of the leads of the multi meter into the ground wire, and the other end touching the positive terminal of the battery?? And test the ohm reading, and post it...
 
In my wiring diagram book it looks like the black with white stripe wire is the ground. It labels the wire as "system return", and it's in the A12 position of the wire harness clip doohickey.

Correct? I don't want to poke the wrong hole....
 
If testing with the connector off the ECM, I'd use a paperclip in the hole where the ECM pin goes. It's safer, plus you MIGHT get luvky and find an intermittent connection if one exists.

It's highly unlikely you've got a flakey ground IMO, something else is going on.

Your CEL problem sounds like EGR to me.
 
Okay so from the ground wire on the ECM to the negative cable at the battery (not hooked up) it scored .03 ohms. I think that's pretty good, tell me if I'm wrong.

There WAS a ground strap running from the firewall that was just hanging there. I might've forgot to reconnect it after the head gasket fix... but I recconeted it to a bolt on the intake manifold. The first time I cranked it over it did the same thing:

Oil pressure gauge lifted a bit, then dropped, then after a little while it went up to 200 kpa, and I did NOT let the truck stop. I just turned off because I knew it would start after that.



Dyeager535 suggested I check that the injectors. He told me to use a noid light to check and see if the injectors are trying to pump fuel while the engine is cranking. So I got my pops so he could crank the engine while I watched thhe injectors.

As soon as he tunred the key the injectors started to pump gas. I could actually see the gas being sprayed, so I knew they were working, and the engine fired up immediately. The turck sat between starts for approx. 5-7 minutes.

When ever I have gotten gas the truck has never started up immediately once I started to crank the engine over. It would try, and almost start, but then die off, and then start up. But never start up immediately.

I am confused as to why the first attempt of starting the truck it took a while, and the second time it fired right up, when it would never ever do that do that before... All from a ground strap??


I am going to let the truck sit for a little while again. I'm gonna give it a half hour, so any priming will have dissipated (hopefully), and I can see if it starts right up again.


But I still have no CEL light on start up. Not even when the key is turned to on, nothing at all....
 
Okay, so I started it up again, and it took the typical amount of time. As in it took a while. Maybe a little less time, but I'll test that theory out tomorrow morning.

I'll also test the injectors tomorrow.

Anymore suggestions on checking the CEL??
 
Sorry was out...you can test ground anywhere, you don't need to go to the battery, just need to make sure you've got a good connection.

Post is getting long, too lazy to doublecheck...is the relay priming when you turn the key to run? (not start) You can't try this multiple times, only once on a cold engine, then wait for a few minutes. I wonder if you don't have something going on with the wiring between the ECM and relay.

Don't jump straight to this next suggestion, do the above, if the answer is that it does NOT prime, disconnect your oil pressure switch and see if it will ever start. It won't take long to know, you already know how long it SHOULD take, if it goes beyond that time, and it still won't start, your oil pressure switch is handling fueling, not your relay, and is why the starts are long.
 
The fuel does not kick in until after the oil pressure gauge hits 200 kpa (or close to it..)

how do I check to see if the relay is working, and still have it plugged into the truck??


Yeah sorry this thread is getting long winded.... I hoped it was going to be something that could be fixed quick and easy.
 
You can check your fuel pump relay by unplugging it and putting your volt meter leads into the coil leads on the connector (they would be the thinner wires), and seeing when they gets 12 volts. When you see it get 12 volts, then the relay is being activated. If you have consistent running at all other times, I would rule out a flaky relay.
edit: to test the relay with it still connected, you'd have to stab the thicker leads coming off the relay connector, and see when they get 12v. If you can find the fuel pump connector before it goes into your fuel tank, you can unplug it there and see when it gets 12v, that would be a better option than stabbing the wires. When you see 12 volts on those leads, then the relay is functioning. That's not a garauntee that it's not bad, though, relays can also fail sporadically, but don't think that's your problem or you'd probably also have stalling issues at other times.

This is all assuming you can be there with the meter while someone helping you goes through your starting routines; turn the key on, crank it, etc. Like dyeager said, in normal cold engine conditions it will only turn on the FP relay once when you turn the key to on, then you have to shut down and wait a few minutes to try again.

I think you should try the oil sender unplug also. See if that has any effect whatsoever.
Are you sure the fuel pump is not being turned on until 200kpa? Maybe something else is involved somehow, like the coil or ign module or something (I can't remember the motor anymore...). Some odd short somewhere that only gets it's closed ciruit when the oil pressure sender passes current...
All the ECM connections were clean?
Have you always had this problem?
Has anything changed since reconnecting the ground strap? When you reconnected it, did you make sure it had a decent electrical bond?
 
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Forget your gauge. We need to know if your fuel pump is working.

Like I said, turn the truck to "run" without starting. Does the fuel pump run? Make sure this is first thing in the day, or the truck has sat a few minutes with the key off, before trying. You'll hear it run.
 
Kind of curious how he knows if the fuel pump is coming to life at 200kPa if the truck starts then? I only searched for one mention, says that once the gauge hits 200kPa fuel pump turns on and it runs...no way I can hear my pump running if my truck is cranking.

I want to make sure there isn't an assumption that's what is going on.
 
In the morning I start the truck without climbing in, so I can go back inside while it warms up. I can hear it pretty good outside the truck, and I geuss I can just pick up the small hummm inside the truck too.... :confused::confused:


I'll test it anyways.

I'll just pull the relay connection right out, and test it there.
 
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Okay, so I went out today to unplug the fuel pump relay wire harness, and test it to see if/when it sends power to the fuel pump, and found that the pink wire coming off of it goes nowhere...

It just kind of ends at a connector that doesn't attach to anything. There is one coming off the coil aswell... I always wondered about these ending electrical wires.

Is it only part of the "hot fuel handling" setup... because if so I don't think my truck is equipped with that.

My schematic book says the hot fuel handling uses either the LO5 and L19 throttle bodies, and my truck has an LB4 throttle body.

SO I didn't test the fuel pump. I didn't want false reading when I should have a pink wire hooking up to something...
 
Pink wire (thought it was red) is a factory test lead. 12V to it forces the pump to run.

Coil wire is for the tach.
 
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