cadallante87

Ok so this fuel system install is driving me up the wall. I'll give you a little history of whats going on, I installed heads, cam, blower last summer started car up and all was well. Over the winter, I hibernated and didn't do anything. Few weeks ago I started the A&A fuel pump install. That's done, I put in about 3.5 gallons of fuel, then I was trying to get the car started and factory fuel pump isn't priming unless I jump the relay. Car will start if relay is jumped. I haven't played with the factory wiring and obviously the pump is good. How do I test if I'm getting a signal from the pcm? Looking at the schematic, it looks like the pcm wire is passenger rear side of relay. Another thing, my auxiliary pumps when I jump the hobb switch I get the pumps to come on but noticed it's not building pressure, maybe this is normal if the factory pump isn't running too?

dadaroo

Not sure how you jumpered the relay. Across the switch contacts or jumpering 12 volts to the pump side contact.

Try swapping a relay in case the relay is bad. If not the relay, verify the fuses in the related circuits are good.

If I knew your year car I would like at the schematic with you.

cadallante87

It's a 98. I've swapped the relay with the AC relay, same result. I was jumping 12v to the pump side contact. 20amp Fuse is good.

cadallante87

I don't know proper terminology so here's a pic of what I'm jumping. Believe passenger front is 12v key on and driver back contact is fuel pump positive.

Chicago1

You should be getting a 5v source at the wiring to the fuel pump harness on the hat. I forgot which wire it was I have it posted in one of my build threads and I see it in other threads. search 5v fuel pump or something like that

cadallante87

Thanks. Wouldn't my problem be before the relay tho if I'm getting pump to turn on while jumped. Maybe I'm wrong. First time playing with fuel system.

Chicago1

I couldn't tell you man hopefully Bill C will chime in he is one of the resident electrical experts

cadallante87

Hoping it's not the pcm. From what I'm reading the 98's are known to do this. It was bench flashed last year for the blower install and ran fine after. Scratching my head here. Hopefully Bill Curly will chime in. Thanks

dadaroo

I have reviewed the 98 schematic and fuse block wiring. I think you need to see if the PCM is activating the coil in the relay by checking to see if you get voltage to the relay coil.

The pin that gets power from the PCM is the one closest to the passenger fender and the windshield.

The Ground side of the coil is the pin that is opposite corner. Near the engine and towards the front of the car.

Pull the relay and check to see if the PCM is providing power when ignition is ON. Next, see and if the ground side is good with an ohmmeter. Ignition can be OFF for this.

You should also try verifying that you are actually getting ignition ON voltage to the relay contacts switch side. Check to see if you get voltage to the pin that is closest to the passenger fender and the front of the car. Based on your jumpering we know the other side of the circuit to the pump is good.


If you want to discuss diagnostics feel free to PM mw with your number and we can discuss on the phone.

cadallante87

Last night I checked the contacts and I had 12v on both passenger side locations with key on. I will check the ground this evening. Thanks for the help!

dadaroo

Keep me informed. Your problem sounds to be a simple one to locate. Just need to find where the circuit issue is. Hope it is not the PCM. I should have told you where the ground is for the coil in case you need to locate. I can do that if you need it. Not at home now.

There is a way you could even bypass the PCM powering of the coil and do it with a new circuit that still required the ignition to be ON to energize. Off the top of my head I don't see any pitfalls in doing it but would want to study that more before designing a circuit for you.

cadallante87

Will do! Thanks for your help!!! If I'm getting power from passenger side/closest to windshield (assuming that is the pcm supply) the PCM sounds fine, if that's the case, correct? I don't mind if it's the PCM, so much, just want to know with certainty. With my car being a 98, I'd like to repin to a 99+ but would like to hammer this problem down before opening another can of worms.

cadallante87

GOT IT! I was testing the ground and it was perfect. Then I dropped the relay and picked it up with a bent pin and thought, hmm maybe I should bend them all out some, and sure enough it made a connection. So my issue is the actual relay port. Can I tighten those connection points? I probably loosened them up while using the jumper!

dadaroo

I knew it had to rather simple to figure out, good job. You can bend the female terminals to make them a tighter fit. However it will require disassembly of the fuse box. If you got it to work it may be fine since there is no relative motion of the item there. Carry a jumper with you just in case. A paperclip can do.

If you want to go into the box I have some info.

cadallante87

Thanks for the help dadaroo! I started opening the fuse box and it looks like a cluster****. I think i'll get some dielectric grease and call it a day. If it does it again, I know where to look first. Now I think it's time to swap the PCM for a 99+ before I get it tuned. So ready to get this car back on the road!

corvettebob1

DO NOT PUT DIELECTRIC GREASE ON THE PINS, it is an insulator.

cadallante87

You got me reading here and looks like you're right on. I use to think it helped the connection. I'll just leave it be then. Thanks

dadaroo

I only use dielectric grease around a connection and never in the current path.

I thought I had info on fuse box disassembly but can't find it.

Understand, if for some reason you get a replacement fuse box they are NOT all the same. I can compare the pin outs for different years to see if they are the same.

cadallante87

Good to know! Would definitely appreciate that knowledge! Thanks dadaroo!