Fuel Pump fuse keeps blowing?


Buick3.8
01-11-2007, 09:08 AM
Ok, So my 1995 Lasabre was runing great after i did a tune up and the TPS on it, even took it from Michigan to Connecticut and back with no problems what so ever(even got 30mpg). Anyway...Last weekend i backed into my driveway to empty out my trunk and left the car runing. I went inside my house...5mins later cam back out...cars not runing.

So first thing i check is spark. Nothing
Next is injector pluse. Nothing.
Next fuel pressure. Nothing.
Thinking i know the ICM goes bad on these cars and can cause that..i replace it. STILL NOTHING. (luckly i was able to return it)
I start checking every single fuse i can find. Finally i found the fuel pump fuse and relay.

Has new relay and 20amp fuse in...Turn the key on..fuse blows instantly.
Thinking(wish i didnt) it was a bad fuel pump drawing to many amps. So i replaced that. NOTHING.

While i was looking at it last nite i hooked up a little dome light to where the fuse goes. If you run some wire to the fuse connection and put a light in the middle it'll light up if its short to ground. Sure enough it is. So i start messing with all the wiring...and i mean all of it. Finally i take the ICM harness off and the light goes out. So i trace it back to the back half of the motor and theres another connector by the injectors. i pull that...light goes out.

So now im kind of stuck between a hard and a hard place. I dont know where the wiring harness goes to. Or if anyones ever had this problem before I"d really really thank you for helping out. I really dont have the money to send my car into the shop...I've always been able to work on my own stuff...just need to know where the wiring harness for the ICM goes to.

Thanks all....I hope i can get this thing fixed.

Bassasasin
01-11-2007, 03:45 PM
Congrats for using the test light instead of a pocket full of fuses.

NOW WHICH FUSE?? F 6? We gotta know!
I dont see a connection to the ICM from the F 6 FUEL pump fuse on the 94' similar schematic.

The ICM wiring goes to a mid engine connector usualy under the alternator. Then on to the firewall on passenger side.

If you have no spark with the F 6 fuse disconnected you have other problems.

I havent heard of alot of ICMs going bad on this forum or others. Often the ICM is targeted for troubleshooting since it is a most logical component. More often the CRANKshaft sensors and coil packs. However, since it's targeted so quickly it may avoid forum attention. Coil packs cause rough running and the CRANKshaft sensor causing jerks at speed, complete stalls or CODE 41.

The fuel pump relay CONTROL (coil) is connected directly to the ECM.. D16 pin connection. Its suppose to.

The Voltage circuit for the running fuel pump comes through Fuse 6 then off to two places at the same time.
1. First to the oil pressure switch then direct to the fuel pump. Basically, with no oil pressure it wont let the engine run by cutting off fuel. It provices source voltage when pressure is up then the fuel pump completes the circuit to ground.
2. The other place is the other side of the relay for PRIME when the engine is first turned on without oil pressure. You normally will see the test light light because it can find a ground until the fuel pump relay is energized..

The F 6 Fuse ONLY has circuits for the fuel pump, oil pressure switch, and fuel pump relay. Those and associative wiring can blow the F6 fuse.

Know whats going on when using a test light to test for ground on a normally end grounded circuit through a component.

Disconnect you fuel pump and use the test light.

I have heard of pinched fuel pump wires close to the tank.


Good luck.

Luke.
01-12-2007, 10:43 AM
An impressively outlined inquiry, followed by an equally impressively detailed response. What a learning lesson....

jdl
01-12-2007, 01:55 PM
The diagrams I was looking at does appear to show, the ignition module and fuel pump working off the same 20 amp no 6 fuse. One diagram even showed the maf sensor working off the same fuse.

With the ignition module B+ disconnected, I wonder if the pump will prime? You may need to use a fuse to protect the circuit. You can check amp draw on the pump circuit.

With key on engine off, I wouldn't think the ignition module would be drawing much current if any. I don't have a spec for that.

Mickey#1
01-12-2007, 03:52 PM
Fuel pump & ICM are on the same fuse.

Can you post a picture of what you unplugged?

Bassasasin
01-13-2007, 12:28 AM
Fuel pump & ICM are on the same fuse.

Can you post a picture of what you unplugged?

Interesting... I was looking at Mitchell OD.. for a 94'

Thanks guys for checking that out..


Bass...

jdl
01-13-2007, 11:03 AM
I'm just surfing today, like always, killing time.

I couldn't figure why the ignition module would blow the fuse, key on, no crank.
Then I got to looking at the module connector, 14 wire connecter, at least that is what my info shows. The crank and cam sensor get their reference voltage through the ignition module, the ref voltage goes hot when you turn the key on.

I wonder if there were any cam or crank sensor codes? With the key off, I might unplug the crank sensor, turn the key on, see if the short was still present, if it is, turn off the key, plug the crank sensor back in, unplug the cam sensor, check if short is still present. If the short goes away, that doesn't mean the sensor is faulty, it might be a wire or connector. Just a thought.

Blue Bowtie
01-13-2007, 12:32 PM
And just for reference, look closely at the schematic for the fuel pump power circuit. You will discover that the auxilliary oil pressure switch does NOT act as a safety shut-off, but is a redundant path for fuel pump power in the event of pump relay failure. No domestic GM engine of that vintage used a pump cut off reliant upon oil pressure.

Lots of people make that assumption when they see the oil pressure switch in the circuit - Even dealership techs, but you can usually win free drinks from them on a bet. Bet then that it will still run with the oil pressure switch unplugged. You can run the sump bone dry and the pump will contiinue to operate so long as there is a relay installed and the PCM has references pulses from the CKP.

That is important, since a failed/grounded oil pressure switch can take out the fuse. Been there.

Knowing what connector you unplugged is going to be very helpful - either identified in a photo or by the wire colors in the connector, since the circuit you have open may not be what we're assuming.

BNaylor
01-13-2007, 01:18 PM
:werd:

:lol:

Yeah I've won a few of those bets. I had a similar issue over at sister "H" body forum Bonneville concerning the oil pressure sending unit and fuel pump circuits. Alot of confusion and misunderstanding on the issue.

Here it is from our main GM man GMMERLIN.



GMMerlin,

Can you do me a favor and help resolve an issue that has been bugging me. On the early to mid nineties GM 'H" body cars like Buick LeSabre and Pontiac Bonneville does the oil pressure switch act as a fuel pump cutoff. I see the replacement part is listed as a fuel pump/oil pressure switch, part # 25627057.

However, I do not see any service documentation supporting that. If oil pressure is nil will fuel be disabled?

I know on a 97 and up "W" body like a Regal or Grand Prix you can disconnect the oil pressure sending unit and the engine will start and run OK.




Bob,
Usually the oil pressure switch worked in 1 of 2 ways.
1. a redundant power feed for the pump, parrallel with the relay...if one fails the vehicle will run off the other
2. sole power source while the vehicle is running.

Unfortunately I do not have any older service information to check right now...give me a couple days and I can come up with more info.



Not finding any good information, but by looking at the schematics and going off memory, the relay energizes the pump for 2 seconds and the oil pressure switch powers the pump while the engine is running.

It appears that the relay is powered up anytime the engine is running(from the ECM) so if one fails (relay or switch) the engine will continue to run.
Hope this helps

Buick3.8
01-13-2007, 06:04 PM
Hey all. This is what i've came up with so far.

First. I've unpluged the OPS, still shorting
unpluged the cam sensor, still shorting,
fuel pump, still shorting


I see the crank sensor plug, But can i unplug it? It looks really tight in there and i wasnt sure if it was possible with the Harmonic balancer still on.


Also. This is a test one of the techs at work told me to do(work for GM Dealer). He told me to take all the coils off and try it. then test again with them back on. He gave me a test ICM to check too.

So. My findings.

All coils pluged in and ICM connector pluged in= Shorts out
All coils unpluged and ICM connected = No short

I didnt try it with each coil seperate yet...it was late that nite. So He gave me a test coil and told me to try one at a time. He says it sounds like a coil is shorting out some how. Does this sound like its possible?

I thank everyone of you for the help with this problem.

Mickey#1
01-13-2007, 08:23 PM
Don't worry about the crank sensor you already found the problem.

I was helping someone on another forum with the same problem. When he removed the coils he said the top of the ICM was gritty. All he did was clean everything up, put it back together & fired it up. You can check the resistance of the primary side of the coils. If they all have the same resistance I'd clean everything up & give it a try. The ICM supplies a constant 12 volts to one side of the coils & then grounds the other side when spark is required so make sure there is no sign of corrosion where the electrical contacts are.

Bassasasin
01-13-2007, 08:58 PM
This post really 'shone' the

"POWER OF....
THE F O R U M,, f o r u m,,,, forum"


High fives !


Special CUDOS.. to you Mickey#1.
Thanks for the insight.

Buick3.8
01-13-2007, 09:09 PM
So you really think its a coil then?

Mickey#1
01-13-2007, 11:11 PM
I think you've got it narrowed down to the ICM or coils. A bad coil or a problem where the coil's electrical contacts connect to the ICM seems like the most likely suspects. Look everything over very carefully then put one coil on at a time & retest before putting the next coil on.

Buick3.8
01-14-2007, 04:08 PM
Well. I cant thank you all enough for the help. It indeed is/was a coil. I checked one by one and sure enough the middle one was bad. It was just really strange how a coil can blow the fuel pump fuse. But never the less...its fixed. Thanks again everyone

jdl
01-14-2007, 05:05 PM
Glad you got it fixed.

Mickey#1
01-14-2007, 05:49 PM
Glad to hear you got it running & thanks for keeping us updated on your progress.

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