Older OBS to LS wire harness setup

[mike205]

Was the fuel pump for a 96 or newer 1500?

[droopyzda1]

Yes. I double checked with a fuel injector pressure gauge at the Schrader valve in the fuel rail. Its at over 55 psi plus or minus.

[kewljay223]

well to me if she's firing with starter fluid, and u have fuel pasture at the rails (which means your pump is working) it sure sounds like the injectors aren't firing. which I believe could only be a few things. vats isn't removed (which u said u did...) or bad injectors/coils.... but if she tries to start with the fluid, then it seems injectors and coils are ok. sounds like a tune issue to me. I'm still new to this but I'm just using the knowledge I have. is there another pcm with the same setup u have that u could try? a buddy or something?

[Mickeymotormount]

I know you said you have all the grounds on, but I would double check again. I remember reading a post here where someone else had a similar situation. Turned out he was missing a ground. The engine must be grounded to the frame and body. Make sure the connections are clean and don't have rust/paint around them. Clean if necessary.

[kewljay223]

mickey is right. there is a chance u got a stray ground somewhere. that happened to me. i was missing one ground which prevented it from firing. i didnt try it with starter fluid like you did. maybe thats the issue. my lose grnd was the one up front down low beneath the ps pump. thats a common mistake aparantly. check all your grounds. theese new motors now days rely on the computer for everything which supplies a gnd to make things work. literally one ground can screw a ton of stuff up. good luck. post back with results

[droopyzda1]

Thanks guys. Unfortunately, I do not have a buddy that has done this swap that I can borrow their pcm. I will double check the grounds. I made two common grounds when I redid the harness. I have them bolted to the accessory bracket next to the alternator. The negative battery cable which comes out of the battery (battery is in the obs original location) is split into to two wires. Smaller One goes to the inner fender well, thick wire to the passenger side of the block. Then I have the the two common grounds bolted on the driver side on the accessory bracket. I then have a thick ground wire from the driver side block to the frame. And lastly a wire from behind the passenger head to the firewall. Does this sound about right? Also when I would check to make sure they were grounded, I would use a test light, with the clip connected to the positive terminal of the battery and touch each of the grounds and it would light up. Was that the corrected way to test them?

[kewljay223]

sounds like your missing some... there should be like 5 grounds or so just from the harness alone.... most of them are in the back. they should be coming out of the harness with ring terminals on them so they can be connected to the bellhousing bolt studs. i know for sure there is the one down low up front on driver side....but you have two??? not sure what the second is..

yes thats a way of testing but it doesnt mean its a good ground. could be just enough to light up the bulb. you should use a meter and set it to the resistance setting and touch one lead to the neg batt and the other to whichever ground you wanna test. the meter should from 1 to 0. if you have numbers, that means that is resistance (ohms) between the two points. that means its a bad/dirty connection or there is a slight cut/pinch somewhere in that wire.

now what i just described is only testing the ground path to the battery and not the wire itself. sounds like you got a decent path on each point, but i really think your missing wires from the harness that go to the pcm. if i was you, i would crawl up in there and look down behind the motor for stray grounds dangling.

[droopyzda1]

Thanks guys !! I double checked the grounds and cleaned them up cause some of them did have paint. I used a multimeter and checked the ohms and theybwere all at 0.3. . She fired right up, but I had to manually accelerate it at the cable for it to stay running. It would shut off if I let go of it. Going to check the resistance of the MAF, TPS, and IAC valve. Maybe one of them is bad. Also what about the truck intake vacuum openings? Could that be a part of the issue? The opening in the back of the intake is connected to the brake booster, I have the original purge valve still in place but the emissions is deleted and reprogrammed that way. I have an opening on the top of the intake but I have a plug over it. I also have a plug on the fuel pressure regulator.

[Mickeymotormount]

The fuel pressure regulator senses engine vacuum to maintain fuel pressure under all engine load conditions. It must be hooked to the intake manifold. You should also have a manifold absolute pressure sensor on top of the manifold. If either of these two are missing, let alone both of them, you will have some running problems.

[droopyzda1]

Thanks mickey !! Sure enough, there wasn't a MAP sensor connected, period !! It was an open hole on top in the back of the intake. I hooked up the scan tool to the obd2 connector and it verified it. I bought one and put it in, but there isn't a plug for it on my harness. I may have taken it out when I redid the harness, but I do not see it in the box where I put the wires that I took out. I will double check tomorrow. Now it starts but I just have to hold the accelerator for a few seconds, let go of it and it idles by itself. Thanks mickey also for the part number of the serpentine belt u used. I got the same one and it works like a charm. I just have to remove some washers I placed behind the custom a/c bracket cause it about 1/4 to far forward and doesn't line up with the other pulleys. I used the 5.3 upper and lower hoses and just trimmed them a bit to fit on the original C1500 radiator. Thanks again everyone, almost done, now all the finishing touches ar3 left.