Where's the Chevy P30 fuel pump relay?

ClydesdaleKevin · January 10, 2014, 12:41 PM

Anyone know where to go about finding the fuel pump relay on an 89 P30 chassis with a 454?

We are vapor locking like crazy again, and I just put in ANOTHER electric fuel pump. I'm going to pull the fuel line off and have Patti start the rig to see if fuel flows out, but if it does or doesn't, I'm starting to suspect either a bad fuel pump relay, loose wiring, or even a bad oil pressure safety switch going to the fuel pump.

We are out in the middle of nowhere, although I have a couple of generic relays that might work if I can find the suspect one. And I'm not above rewiring the pump to bypass the OP safety switch if necessary, or rewiring the pump altogether temporarily to a toggle on the dash if necessary...lol!

Thanks!

Kev

legomybago · January 10, 2014, 03:20 PM

Arent they down on the left side of the engine...almost under the drivers feat? I thought I read that somewhere?

Froggy1936 · January 10, 2014, 08:19 PM

Hey Kev You will have to get the specific wireing diagram for that veh. Looking thru my stuff nothing seems the same ! Usually fuel pump relays are easily accessable & have an open female connector close by to hot wire pump . One thing if you rewire the pump be carefull there are two wires at the sending unit one power for pump the other fuel gauge rheostate Do not supply 12 V to fuel gauge it will be destroyed or cause explosion ! If your veh uses a relay The common Chevrolet relay wires are Tan & White , Orange 1, Orange 2 , Black & White , Green & White . The oil press switch supplys the ground for the relay when there is oil pressure . Frank

ClydesdaleKevin · January 11, 2014, 09:51 AM

Thanks Frank! First I'll pull the fuel line and have Patti start the engine to see if we have fuel flow. Once that is confirmed...or not...I'll start checking the engine block for the oil pressure switches and make sure the wires going to them are connected. Then trace that wiring hopefully back to the relay.

Thanks again!

Kev

bluebird · January 11, 2014, 10:00 AM

Kev, my fuel pump relay is under the hood almost center and attached to the bulkhead. On mine there are 3 relays mounted together, fuel pump, ac compressor, and heater motor. These are Bosch cube type relays, mine are black, but I've seen some gray ones on other GM vehicles. The relay will have four wires in it I believe. I'll look in my book to see the color code in a bit, and post

Well the book shows 3 places it could be. 1 where I already said, 2 under the doghouse on drivers side, 3 inside of the frame rail in the rear.

The relay should have 4 but could have 5 or 6 wires in it. The orange wire is 12v power, black= ground, dk/grn/wht is switched power, gray goes to the pump. It may also have a prime relay connected to it with red wires.

Rickf1985 · January 11, 2014, 12:29 PM

Kevin, I am in the same boat but it has been below zero here so I have not done any searching. What you need to do is follow the wire from the oil pressure switch, left side of engine behind the steering pump, and one of those wires will lead to the relay. The other will lead to a ground on the block or body. The safety switch is on a tee with the engine oil pressure sender. the pressure sender will only have one wire.
This is assuming what Frank said is true about the switch supplying the ground. You should be able to unplug that switch and with a paper clip or jumper wire bypass the the switch and then when you turn on the ignition you will have the pump running. If you do not then shut off the ignition and take your jumper off and turn the ignition back on and check the two wires in that plug for power with a meter or a test light. One should have power, ground that wire to a good ground and the pump should run. If it now runs then the other wire is not grounded good. When you ground the wire that has power at first just brust it against the ground. If you get a LOT of sparks then you might want to recheck the circuit and make sure this is not a feed circuit TO the pump. It SHOULD NOT be but I have seen things like this happen before.
Any questions be sure to ask. My e-mail is rickf1985@comcast.net. You will probably get a quicker response.

bluebird · January 11, 2014, 02:47 PM

If you touch that power wire to ground, you WILL blow the fuse, for sure.
That relay should have power on one leg all the time, then another should have power with it running.

Rickf1985 · January 11, 2014, 05:24 PM

The wire we are talking about is the wire going through the oil pressure safety switch which is what closes the the relay. That should be the ground wire. The wire at the safety switch will NOT be the wire that powers the fuel pump. I will try to find a diagram to verify but that is standard procedure.

ClydesdaleKevin · January 12, 2014, 09:03 AM

Thanks guys! I'll be sorting this all out in a few days, and then let you all know my findings.

Anything else you guys find out, please let me know!

Kev

gary19734 · January 13, 2014, 09:50 PM

Hey kev have wire diagram too big to post on site send me your email address and ill send it to you send it to gjtimney AT aol. DOT .com good luck Gary

ClydesdaleKevin · January 14, 2014, 10:28 AM

Thanks Gary! I shot you an email.

Kev

DaveVA78Chieftain · January 16, 2014, 02:41 PM

Source: Page 7-102 (H5D Emissions section) of the Chevy Motorhome Service Guide

Oil pressure switch is in this circuit. This is a dual function switch (oil pressure and fuel safety cutout)

Refer to pdf page 139 (7-44) for mechanical layout

Refer to pdf page 141 (7-46) for electrical layout

Happy Trails to you,
Dave

ClydesdaleKevin · January 17, 2014, 10:06 AM

Thanks Dave! I saw a relay that looks like that in the front compartment screwed to the firewall when I did my headlight project. It looked pretty crispy as I recall.

I'll take a closer look today.

Kev

ClydesdaleKevin · January 17, 2014, 05:33 PM

BINGO!!! Once again, Dave has come through with flying colors!

The relay was even approximately where the diagram Dave listed says it is...although I didn't see it at first, expecting it to be nearer to the back of the engine.

To find it, I first had to find the oil pressure sender, which is at the FRONT of the engine...the front lower driver's side corner of the engine block, directly under the power steering pump and AC pulleys if you dropped a plumb straight down.

Looks to be in decent...although original...shape, and isn't leaking oil. Seems to only have one wire going to it, and then that wire joints a cluster of wires that goes up to the side of the doghouse opening, just like Dave's picture, but towards the front of the compartment. In the back there is a plug in the oil galley, so I'm guessing this is an alternative location.

Anyhow, I followed those wires, right to a big relay, marked with the same GM part number as Dave's illustration, 15528707.

Which is right next to an even bigger relay that is somehow part of the AIR system.

Anyhow, found it...now I just have to figure out how to troubleshoot it! I suppose I could replace the sender and the relay, but I hate replacing things that I'm not sure are broken.

Anyone have a clue as to how to test the relay to see if it is good? The sender seems to be good, since it sends the signal to my dash meter to read between 60-80 psi...although it tends to either read nada when turned off, and a steady 80psi (just under) regardless of RPMs. The meter only goes up to 80.

And if I wanted to bypass the safety switch part of the relay, which wire would I either ground or send to 12 volts?

Kev

ClydesdaleKevin · January 17, 2014, 05:46 PM

I may have just answered my own question by typing in GM 15528707 on Google.

This is from a Barth owner's website:

"Those of you with late 80's Chev chassis will have a "hybrid" fuel system. (Mechanical fuel pump and carb but also an electric pump in the tank.) The pump is run by the fuel pump relay GM 15528707. (see the 1996 Chev Motor Home guide Appendix 7-7 page 7-44 to 7-46)

The relay has 2 functions: it supplies power to the fuel pump during cranking and while running but shuts off if oil pressure is lost. Also it supposedly has a delay timer to cycle the pump for 5 seconds prior to startup. (This, and the color coding for the relay, from page 7-46)

Bad news: this relay is required for engine operation, prone to failure, the part is not available anywhere I know of, and the relay diagram is vague about which wire does what inside the relay.

Good news: it's just a standard single pole (5 wire) relay with a timer inside.

My Barth was slow to start after sitting due to dry carb bowl. I have manual fan switches to run after shutdown to reduce heat soak but carb still needs priming. Inspection of the relay (a tight fit under the forward left side of the doghouse near AC compressor and too tight for pics, sorry) revealed an empty relay case attached and another relay hanging from the wires. My relay did not have the 5 second cycle working. Search for replacement was dead end.

To take care of both problems I replaced the relay with the generic 5 pole type (same as the headlight relays, fan switch relay, etc.) I also added (dashed lines in drawing) a normally open switch to trigger the relay for manual priming. After sitting for some time, I hit the prime button about 15 sec and the engine started promptly!

If relay 15528707 fails, you'll need this info...
The black and dk blue wires are interchangeable.

I happen to have a spare 5 pole relay from my headlamp troubleshooting from a while back, so I might just go ahead and try this!

If his wire colors are correct, it even looks like I could directly bypass this thing in a pinch where he added in a priming switch, and the priming switch isn't a bad idea either!

I'm gonna try it!

Kev

DaveVA78Chieftain · January 17, 2014, 10:53 PM

For Reference:
You do realize that all this information is from the free book (Member Area, Manuals, Diagrams & Tech Info, scroll down to chassis section and select Chevy/GM P-30 Service and Maintenance Manual). Both I and the Barth write up are referrencing pages in that book.

Dave

pvoth1111 · January 18, 2014, 07:35 AM

I was thinking about this and you could be running out of timing advance or be having some other distributor problem...even timing chain stretch could cause vapor lock like issues....I remember you were playing with your timing a while back.

ClydesdaleKevin · January 18, 2014, 08:46 AM

I only advanced the timing a hair, enough to raise the idle from 700 rpm to around 900-1000, then dropped it back down with the idle screw.

While its possible, I doubt I have any significant timing chain stretch yet at 110K miles.

And it ran great at the new timing settings all the way from St. Marys, GA, down through Jacksonville, FL to I-10, and all the way across the country to about half way through Texas. Then it started the vapor lock symptoms again, and I drove the Jeep to an auto parts store...the electric fuel pump that I had just installed a year ago had stopped working, so I bought another fuel pump, installed it, and it seemed to fix the problem. Then we were good all the way to Tombstone, AZ. It started this vaporlock crap again once we about 80 miles away from Tombstone and back on I-10, on our way to Safford, AZ.

The reason I'm zeroing in on the relay is that I don't think it was the fuel pump...I think its the relay on its way to failure. My reasoning is this. When in my sister's driveway troubleshooting the fuel delivery problem for the genny, I removed the fuel pump from the tank to double check which pickup tube was which. Then of course, once I reinstalled it, I had to test it. I had Patti turn the key, and there was no fuel flow. I had her turn the key again and start the engine, and still no fuel flow from the electric pump. The third time, without touching any wires or anything, the pump started flowing fuel.

When it went out in Texas, I figured maybe the pump went bad, installed a new one, and we were fine until Tombstone.

Then it crapped out again, and there is no way another new fuel pump went out. Gotta be the relay or connections.

Kev

DaveVA78Chieftain · January 18, 2014, 10:59 AM

From the Service book:

There can be a bit more to the original circuit than you may be aware of. Barth drawing is a variation of this. I believe the Barth approach removes the 5 second "prime" circuit contained in the original relay.

Dave

Froggy1936 · January 18, 2014, 01:38 PM

Kev i have found that when you have trouble with anything more than twice Eliminate all of its components . I would install a holly fuel pump back near the tank (should be as low as possible) Install a common H/L relay with a switch direct from batt source with its own wireing fused 30A . If problem occured again turn on aux pump this will cure loss of fuel and eliminate any balky orig switches & relays . To me to keep on trucking is the goal fixing malfunctioning parts is not important They can work or not work that is there option but i am not stopping to find the problem Frank!

ClydesdaleKevin · January 18, 2014, 04:19 PM

Ruh Roh Shaggy!

Apparently the Barth is wired quite differently from ours!

I hooked the 5 pin relay up just like the drawing from the Barth website, using jumper wires from the pink wire to the blue wire, up to an unused toggle switch on my dashboard. Made sure that switch was OFF. Turned on my chassis power, then turned the key to "on".

And the relay immediately engaged the starter in the "on" position! Not even in the "start" position, but "on"! Turned off the key...CRAP!!!

Checked for any shorts, maybe spade terminals touching, and nada. Tried it again, and same thing! Starter engages in the "ON" position!

Okay...something is screwy!

The relay I have has the exact same pin layout as the Barth drawing, and if I recall from my headlight project last winter, it was a leftover universal headlight/foglight relay, rated at 30 amps.

So something isn't translating from the original fuel pump relay to the 5 pin headlight relay...so I must have one or more wires plugged into the wrong spot/s.

Any of you electrical gurus have a better idea of how to wire in a 5 pin headlight relay into the system that will make it work similarly to the relay diagram that Dave just recently posted?

Unfortunately the relay I used doesn't have a diagram printed on it, or else I might be able to figure it out myself.

Thanks guys! Stuck in the desert till we fix this...lol!

Kev

Froggy1936 · January 18, 2014, 04:33 PM

See reply 19 before you let the smoke out of all the wires. Obviously you supplied power to the purple wire wich energizes the starter ! You want to go from Pink to your switch thenfrom the switch to the tan and white That will eliminate all when switched on to run pump (if the switch is good) Frank

ClydesdaleKevin · January 18, 2014, 04:46 PM

okay...might have sort of figured something out.

I pulled the relay to look at it more closely, and guess what? The engine won't start at all without a relay in place.

Anyhow, I looked at the relay carefully, and maybe its just an odd bird relay?

Unlike all the diagrams I found for 5 pin headlight relays, this one on its own diagram doesn't have an 87 and an 87a...but rather it has 2 87s connected to each other at all times. 86 comes into one side of the coil and 85 into the other. From the coil is a line that goes to switch 30...which closes the circuit to 87------87

All the other relay diagrams I've seen toggle between 87 and 87a, not leaving them connected together.

Anyone seen this before? I can't even find a similar diagram online to show you what I'm talking about.

Kev

ClydesdaleKevin · January 18, 2014, 04:50 PM

So yep Frank. Since pin 87 is constantly connected on this relay to pin 87 (which on every other relay I've ever seen is an isolated 87a), then the pink ignition wire is supplying 12 volts to the purple wire which goes to the starter relay.

Geesh!

I'm going to go check my electrical box and see if I have any other relays in there...

Kev

ClydesdaleKevin · January 18, 2014, 05:26 PM

THIS is what the diagram on the relay I'm trying to use looks like:

Image no longer available

Except 87b is marked simply as 87, as is the other 87.

And on the relay diagram, the 86 is on the top of the coil, and the 85 is below the coil, but I don't think that part matters.

Anyone think I can make this work, even if I have to jump or connect a wire or two? At this point I just want to get it running and the fuel pump running...I don't care a hoot about the oil pressure safety shutoff for now.

Kev