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Discussion Starter #1 (Edited)
i was having an issue with my truck idling at a low rpm, and one of the suggestions was to switch out the lift pump.

before i was able to, one of my tstat bolts snapped and started dumping my coolant all over the driveway. fixed the bolt, put in a temp gasket, topped up my coolant and on my way.

the next day i switched out the gasket, and brought yard waste to the disposal site and back (5 km trip). got back and my truck smelt like diesel bad. looked underneath and there was a drip drip. turned out the tstat fuel line cracked when i replaced the gasket, cut the line and put the fuel t back on lower on the hose. started the truck and it died soon after, tried to jump the pump and the pump would not power on.

dont know how long my lift pump was not working, my truck has been fishbitting a bit since i bought it. sometimes really bad sometimes not at all, so when my truck has been fish bitting recently i didnt know that my pump had no power. dont know if the fishbitting was always caused by the pump, an electrical issue or something...

i took off the stock lift pump, put on the walbro, plumbed it in, wired a plug onto it. i took a battery and manualy jumped the pump right to a battery (to prime the system), it ran good. i tried to jump the pump onthe ops mod like before, pump didnt run. i disconnected the pump and turned on the truck, the output to the pump on the ops relay had power with a test light but the lift pump harness (one thats on the truck, lift pump is not plugged in right now) does not have power.

i ran a new wire from the ops relay to the lift pump and put it into the harness. lift pump would not run, no power at the ops relay. if i jumped the wire the lift pump ran though. now that points to the ops?

so i went to parts store and got a ac delco ops, put it on and no power to the output on the ops relay.

when the truck is running, i put a pressure guage on the tstat. there is no pressure until i jump the pump to the ops, then over 10 psi pressure. i stop jumping it and it goes back to vacuum.

any thoughts, i am ticked off by this truck lol - next step is to rip apart my ops mod wiring and look at all of that wiring?
 

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If all the wiring checks out, then check to see if the relay is working.

Attached is a OPS mod wiring diagram.
x2 ..... also double check the grounds.... clean and tight:HiHi:
 

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Discussion Starter #5
How can I bypass the ops so the lift pump comes on with the truck like normal? Just for tomorrow, then I have a week to troubleshoot. My gf needs my truck tomorrow and I don't want my ip strained for another day..
 

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LPR Maint Jumper and/or Emergency Repair ;)


Note: With paperclip (PC) installed as shown, LP will only activate with the ignition "ON" regardless if the engine is running or not.
In other words, the GF wont have to worry 'bout turning it on or off as she does her thang...

Good Luck.
 

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Discussion Starter #8
LPR Maint Jumper and/or Emergency Repair ;)


Note: With paperclip (PC) installed as shown, LP will only activate with the ignition "ON" regardless if the engine is running or not.
In other words, the GF wont have to worry 'bout turning it on or off as she does her thang...

Good Luck.

How would I do this with a 94? Pull the plug from the lift pump relay on the firewall and stick a paper clip in there?
 

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How would I do this with a 94? Pull the plug from the lift pump relay on the firewall and stick a paper clip in there?
Not so fast, I was mistaken. No doubt crankme or another member will be along to offer a better way shortly... Otherwise you may have to pull the jumper out when not in operation..
Although very simular, Im not completely familiar with the specifics of '94 wiring harness nor where the LPR is located on the firewall. I can only speclate the '94 and '95 OBD1 models utilize the same LPR and LPR/wiring plug configuration. I appologize for the confusion..


With the paper clip installed the pump will run continuously. Shoot me a pm if you want it to come on with the ignition
I suspect your correct crankme, Ive never tried it with the ignition "OFF." I hadn't given it any thought until you said otherwise.. Thats how I was shown to do it years ago, so I assumed it to be accurate info. My bad.
The real kicker, I knew better last night or I should have.. I just hadn't connected the dots yet.
Fact is.. I peeked under the skirt of the Convenience Center last night, specifically taking note (and pic) of the LPR wiring for another simular case of mistaken identity with DLC Pin Assignments for '95 OBD1 models.
My trick appears to connect ECM-B+ (B1 ORN) straight to LP (A3 GRY) which would make the LP runs constantly just as you say... However next time Im under the hood, I'll pop in the jumper with ignition OFF to further verify. Thanks for the correction.
 

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Relay may be bad?
 

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Discussion Starter #11
So new lift pump relay from parts store, disconnect new wire, re attach the original wire and off to the races?
 

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Discussion Starter #14
i applied 12v to terminal g, nothing happened. but the wire that normally goes to the lift pump is disconnected at the lift pump relay and a new wire is running there.

running a new wire skips the lift pump relay? will this cause any issues?

i took a loose wire and put one end of it against the ground on the lift pump relay and the other on the negative terminal of my battery, my lift pump then turned on. so bad ground on my ops mod was stopping my new wire from working.

although i still dont know why the factory wire from ops mod to lift pump wasnt working... will my new setup cause any problems, its still controlled by the ops, correct?

thanks guys
 

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Discussion Starter #16
ok so the purple lines are where i spliced in the new wire, and the thin penciled in line is the new wire.
 

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Discussion Starter #18
ok so i need to fix the original problem so then i get back the prime while cranking and terminal g.:banghead:

In the mean time, this will get me to and from work without killing my ip..:thumb:

Thank you Racer55, you seem to be solving all of my problems:clap:
 

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crscrs, going to ask a couple favors that will hopefully satisfy a nagging doubt I've always had, but no way of investigating for myself.
Given recent revelations about my own '95 model, my nags seriously inflamed... :hehe:
Seems what was considered impeccable information for nearly 20 years until just recent was shown to clearly be a misinterpretation of the '95 Service Manual. Much of the misinformation still swirling 'bout the '95 models started with the '94's, so Im questioning the validity of previously thought foregone conclusions, not questioning anyones intellegence..
I've always suspected the '94 & '95 models are much more alike than different, contrary to popular belief. If my nag is wrong, no harm done.


Favor 1. Perform an OBD Systems Check (paperclip style of course).
Does the initiating (flashing) sequence ALWAYS begin and/or end with DTC 12 and progress into any present or stored DTC's. OR does it skip 12 and immediately start with any DTC(s) that are (if) present just as the '95 OBD1models?

Favor 2. Look closely at your DLC, noting which slots are occupied or empty.
My interest lies only in DLC pins F & G at the moment. If occupied, could you PLEASE take a peek at the corresponding wire(s) and let us know what they are?
If my nag is correct, your going to find a RED wire at DLC Pin "F" and a blk/wht wire at DLC "G" if you have oem Keyless Entry (molule).


..... pics and/or video too much to ask? :hehe:
 
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