1998 Jimmy: Fuel pump diagnostic questions
#1
11-21-2015 | 03:35 PM
1998 Jimmy: Fuel pump diagnostic questions
Ok - We have a 1998 GMC Jimmy SLE 4dr, 4wd, 4.3L.
The Jimmy has about 140k miles on it but engine is a GM Goodwrench crate motor (installed earlier this year) with about 5000 miles on it. I do not think the fuel pump has ever been replaced. I'm assuming this is going to be a fuel pump replacement but just running the symptoms by to get a second opinion.
Approximately 5 days ago Check Engine light came on & it threw a code for bad O2 sensor - cleared that.
Ran fine until Thursday night, no issues & O2 sensor code never came back.
Friday morning: starter cranks but engine will not start and run. Showed code for faulty MAF sensor... which it wasn't. New MAF = no change. Cleared code & replaced MAF with one that was on it.
Starter fluid does start it up briefly. Gasoline into throttle body also will get it running briefly... so it has spark to plugs and based on how smoothly it was running I don't think there is an issue with the cam or crank sensor (both replaced with new engine).
Son had added gas night before but I added a gallon 'just in case' - shows at 1/2 tank.
Checked fuel pressure... Zero! Swapped around relays and fuses - no change. Fuel pump still not running. Pump relay does click/energize with key 'on'.
At one random attempt to start and for JUST ONE TIME the fuel pump ran briefly & test gauge showed 40psi fuel pressure (way too low... but more than zero!)
Ran jumper wire to fuel pump test port in underhood fuse box (Thanks Capt Hook!) & still got nothing from pump - didn't run.
Banged on fuel tank while son tried to start - didn't kick in at all.
Security light goes out as 'normal'. If I understand correctly; a problem with the security system will allow engine to start & then shuts off fuel pump after a second or two... pump doesn't run at all here.
Question:
Am I missing anything obvious?
Any other way to measure voltage to the pump? Looks like the only way to check for voltage at the pump is to drop the tank to access connector. (And if ya do that... might as well replace the pump with this many miles...)
Dropping the tank tomorrow so any suggestions appreciated! (Especially if I don't have to drop the tank!
) Thanks!
The Jimmy has about 140k miles on it but engine is a GM Goodwrench crate motor (installed earlier this year) with about 5000 miles on it. I do not think the fuel pump has ever been replaced. I'm assuming this is going to be a fuel pump replacement but just running the symptoms by to get a second opinion.
Approximately 5 days ago Check Engine light came on & it threw a code for bad O2 sensor - cleared that.
Ran fine until Thursday night, no issues & O2 sensor code never came back.
Friday morning: starter cranks but engine will not start and run. Showed code for faulty MAF sensor... which it wasn't. New MAF = no change. Cleared code & replaced MAF with one that was on it.
Starter fluid does start it up briefly. Gasoline into throttle body also will get it running briefly... so it has spark to plugs and based on how smoothly it was running I don't think there is an issue with the cam or crank sensor (both replaced with new engine).
Son had added gas night before but I added a gallon 'just in case' - shows at 1/2 tank.
Checked fuel pressure... Zero! Swapped around relays and fuses - no change. Fuel pump still not running. Pump relay does click/energize with key 'on'.
At one random attempt to start and for JUST ONE TIME the fuel pump ran briefly & test gauge showed 40psi fuel pressure (way too low... but more than zero!)
Ran jumper wire to fuel pump test port in underhood fuse box (Thanks Capt Hook!) & still got nothing from pump - didn't run.
Banged on fuel tank while son tried to start - didn't kick in at all.
Security light goes out as 'normal'. If I understand correctly; a problem with the security system will allow engine to start & then shuts off fuel pump after a second or two... pump doesn't run at all here.
Am I missing anything obvious?
Any other way to measure voltage to the pump? Looks like the only way to check for voltage at the pump is to drop the tank to access connector. (And if ya do that... might as well replace the pump with this many miles...)
Dropping the tank tomorrow so any suggestions appreciated! (Especially if I don't have to drop the tank!
) Thanks!
Last edited by lunghdlunghd; 11-21-2015 at 03:37 PM.
#2
11-21-2015 | 09:00 PM
does sound like pump. dropping the tank isnt all that hard. When I did my 98 the hardest part was disconnecting the fuel lines from the pump. Get new straps also. and theres a vent on the front of the tank also. You may be able to access the power connector before dropping it. thicks wires are for pump thinner wires are for fuel guage, good luck
#3
11-22-2015 | 12:37 AM
Junior Member
Joined: Oct 2015
Posts: 322
From: Louisiana
Ok - We have a 1998 GMC Jimmy SLE 4dr, 4wd, 4.3L.
The Jimmy has about 140k miles on it but engine is a GM Goodwrench crate motor (installed earlier this year) with about 5000 miles on it. I do not think the fuel pump has ever been replaced. I'm assuming this is going to be a fuel pump replacement but just running the symptoms by to get a second opinion.
Approximately 5 days ago Check Engine light came on & it threw a code for bad O2 sensor - cleared that.
Ran fine until Thursday night, no issues & O2 sensor code never came back.
Friday morning: starter cranks but engine will not start and run. Showed code for faulty MAF sensor... which it wasn't. New MAF = no change. Cleared code & replaced MAF with one that was on it.
Starter fluid does start it up briefly. Gasoline into throttle body also will get it running briefly... so it has spark to plugs and based on how smoothly it was running I don't think there is an issue with the cam or crank sensor (both replaced with new engine).
Son had added gas night before but I added a gallon 'just in case' - shows at 1/2 tank.
Checked fuel pressure... Zero! Swapped around relays and fuses - no change. Fuel pump still not running. Pump relay does click/energize with key 'on'.
At one random attempt to start and for JUST ONE TIME the fuel pump ran briefly & test gauge showed 40psi fuel pressure (way too low... but more than zero!)
Ran jumper wire to fuel pump test port in underhood fuse box (Thanks Capt Hook!) & still got nothing from pump - didn't run.
Banged on fuel tank while son tried to start - didn't kick in at all.
Security light goes out as 'normal'. If I understand correctly; a problem with the security system will allow engine to start & then shuts off fuel pump after a second or two... pump doesn't run at all here.
Question:
Am I missing anything obvious?
Any other way to measure voltage to the pump? Looks like the only way to check for voltage at the pump is to drop the tank to access connector. (And if ya do that... might as well replace the pump with this many miles...)
Dropping the tank tomorrow so any suggestions appreciated! (Especially if I don't have to drop the tank! ) Thanks!
The Jimmy has about 140k miles on it but engine is a GM Goodwrench crate motor (installed earlier this year) with about 5000 miles on it. I do not think the fuel pump has ever been replaced. I'm assuming this is going to be a fuel pump replacement but just running the symptoms by to get a second opinion.
Approximately 5 days ago Check Engine light came on & it threw a code for bad O2 sensor - cleared that.
Ran fine until Thursday night, no issues & O2 sensor code never came back.
Friday morning: starter cranks but engine will not start and run. Showed code for faulty MAF sensor... which it wasn't. New MAF = no change. Cleared code & replaced MAF with one that was on it.
Starter fluid does start it up briefly. Gasoline into throttle body also will get it running briefly... so it has spark to plugs and based on how smoothly it was running I don't think there is an issue with the cam or crank sensor (both replaced with new engine).
Son had added gas night before but I added a gallon 'just in case' - shows at 1/2 tank.
Checked fuel pressure... Zero! Swapped around relays and fuses - no change. Fuel pump still not running. Pump relay does click/energize with key 'on'.
At one random attempt to start and for JUST ONE TIME the fuel pump ran briefly & test gauge showed 40psi fuel pressure (way too low... but more than zero!)
Ran jumper wire to fuel pump test port in underhood fuse box (Thanks Capt Hook!) & still got nothing from pump - didn't run.
Banged on fuel tank while son tried to start - didn't kick in at all.
Security light goes out as 'normal'. If I understand correctly; a problem with the security system will allow engine to start & then shuts off fuel pump after a second or two... pump doesn't run at all here.
Am I missing anything obvious?
Any other way to measure voltage to the pump? Looks like the only way to check for voltage at the pump is to drop the tank to access connector. (And if ya do that... might as well replace the pump with this many miles...)
Dropping the tank tomorrow so any suggestions appreciated! (Especially if I don't have to drop the tank!
) Thanks!Last edited by Toocute350; 11-22-2015 at 12:41 AM.
#4
11-22-2015 | 12:39 PM
does sound like pump. dropping the tank isnt all that hard. When I did my 98 the hardest part was disconnecting the fuel lines from the pump. Get new straps also. and theres a vent on the front of the tank also. You may be able to access the power connector before dropping it. thicks wires are for pump thinner wires are for fuel guage, good luck
Thanks for the heads up on that front vent hose - would have missed it.
Straps - I see why you said that... but your warning was enough for me to PB Blast the front strap & then use vice grips to hold it until the nut broke loose. I would have been cussing a broken strap otherwise - thanks!
Just drained the tank... getting the filler & main vent hose disco'd were a pain after 17 years they didn't want to come loose!
#5
11-22-2015 | 12:43 PM
Just as soon as I can find out how to disconnect those damned "quick connect" fittings the tank is ready to come out. (Ordering some of those things too since I know I'll break them if I don't.) Appreciate the input.
Snapping photos of anything that seems relevant & will post it up for the next guy/gal who needs it.
#7
11-22-2015 | 01:14 PM
Super Member
Joined: Sep 2013
Posts: 1,150
From: wyoming
when I have a tank down I check it well externally for rust spots - I usually clean it well then I coat it with dupacolor pickup bed liner except for the fuel pump mounting ring and the pump its self - I kinnda figure a couple cans of bed liner beats dropping the tank again later for a seeping leak - been there done that 
#8
11-22-2015 | 01:33 PM
This guy has a few fantastic videos on how to replace the pump including tank removal so rather than post up my lame pictures I'll just link to his videos:
How to drop tank on late model Jimmy / Blazer:
Part two:
Part three (replacing tank):
How to drop tank on late model Jimmy / Blazer:
Part two:
Part three (replacing tank):
Last edited by lunghdlunghd; 11-22-2015 at 04:57 PM.
#9
11-22-2015 | 01:38 PM
when I have a tank down I check it well externally for rust spots - I usually clean it well then I coat it with dupacolor pickup bed liner except for the fuel pump mounting ring and the pump its self - I kinnda figure a couple cans of bed liner beats dropping the tank again later for a seeping leak - been there done that
) From riding old motorcycles I remember using a tank liner product that went into the bike's (empty & clean!) gas tank. Ya pulled the tank, cleaned it, made sure it was dry inside & then poured in the sealant and sloshed it around. (You can't always find a tank for an old Norton & ya hafta make do if you want to keep a stock tank on the bike.)
Can't remember product name but google will likely turn it up. It lines the entire fuel tank with a seamless, leakproof coating and that along with your external coat, would buy years on an old tank!
Last edited by lunghdlunghd; 11-22-2015 at 05:01 PM.
#10
11-22-2015 | 07:38 PM
Then again, the tank was put in not too long before we got it, and I cut and hinged up an access panel in the rear of the truck so I do not have to drop the tank.