90 BRONCO NO POWER TO FUEL PUMP

90 bronco no power to pump. wife was driving the thing when it quit. there was a bump in the road and when she went over it the vehicle was jarred and just quit. turn the key and it doesn't even make noise. checked inertia switch first. it was not tripped, , looked like the connector got hot. replaced a perfectly good fuel pump. replaced a fuel pump relay. low voltage to inertia switch. used code reader, got a pcm code and a pcm ground code. had pcm reconditioned, replaced fuel inertia switch, and its melted connector, new battery, battery connections tight and clean, turned the key and nothing happened. code reader still says pcm ground. have crawled all over looking for bad ground connections. can not find it. been down for over six months. any suggestions will be greatly appreciated as long as some a--hole doesn't say buy a chevy.

Which pump are you working on, the frame-mounted or in-tank? I've been looking at some wiring diagrams lately in the Haynes repair manual. That or the Chilton's one may help you trace the short or bad ground so you don't melt anyhing else, JSM84

your enertia switch could be bad and check your fusible links coming off the starter solenoid, i had the same problem i replaced all brand new for $90. or go to junk yard and get for maybe 10 bucks.

This is a very simple circuit to trouble shoot. Instead of throwing parts at it, get a meter and check the voltage along the entire path. Turn the key to ON and use a long wire lead lead connected direct to the battery (-) and look for 12V at each connection. Probably the quickest is to measure at each of the fuel pump connectors, if you have 12V at both, then you most likely have a ground problem. If you don't move back to the next point and check until you find 12V, at that point you have found the culprit. If it turns out to be a ground problem, run a new ground lead from the battery (-) to the negative lead of each fuel pump.

Good luck,

>-

Justshootme84 said:

Which pump are you working on, the frame-mounted or in-tank? I've been looking at some wiring diagrams lately in the Haynes repair manual. That or the Chilton's one may help you trace the short or bad ground so you don't melt anyhing else, JSM84

Click to expand...

It's an in tank model.

Seabronc said:

This is a very simple circuit to trouble shoot. Instead of throwing parts at it, get a meter and check the voltage along the entire path. Turn the key to ON and use a long wire lead lead connected direct to the battery (-) and look for 12V at each connection. Probably the quickest is to measure at each of the fuel pump connectors, if you have 12V at both, then you most likely have a ground problem. If you don't move back to the next point and check until you find 12V, at that point you have found the culprit. If it turns out to be a ground problem, run a new ground lead from the battery (-) to the negative lead of each fuel pump.
Good luck,

>-

Click to expand...

Thanks Seabronc. I'll try what you said, I never would have thought to add a new ground to clear the trouble. I'd also heard that a clogged oil filter can send a signal to the pcm and it will not allow the fuel system to work. That's not the problem here, but it's another possibility.

PonyXpress said:

It's an in tank model.

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The 90 has two 2 fuel pumps, one in the tank (low pressure) and one on the frame rail just about under the driver seat (high pressure). You will have to get to the connectors to make the measurement. I wouldn't suspect ground unless you have 12V at both connectors. If not follow the diagram all the way back to the fusible link.

Don't change a part until you find the most likely one, it will save you a lot of money replacing perfectly good parts. Keep in mind those connectors at each location have been there for 17 years and most likely haven't been apart. A lot of corrosion could have built up in that time. You need to check for the 12V at each side of a connector where that is the only component in the path being checked. Pierce the wire with a pin on either side.

As far as grounds go, I no longer use body and frame grounds as my path for functional components. I use a ground distribution system and run independent grounds to components that need them. The conductivity of frame and body ground is approximately 10th of copper. Also the connections often build up corrosion in the form of rust which makes them perform even worse. That has cleared up any ground related problems I had, one significant one that is complained about is the accuracy of the fuel gauge. A lot of times the fuel sender gets replaced when the problem is actually a poor ground. Mine for ex. would read 1/4 when the tank (33 gal) was only down 10 to 15 gal, since running a new ground it is pretty close, I still have 5 gal when it hits a needle above E.

Good luck,

>-

Per my manual:

These trucks employ a single, high pressure pump which is part of the modular, In-Tank Reservoir (ITR) assembly. Besides the pump, the ITR consists of a venturi jet pump, a supply check valve and a shuttle selector valve. All this is mounted on the fuel gauge sender ******. The sending unit is separate from the ITR module.

I have to agree with seabronc on that one. I'm 95% sure that a 90 was still using the low press. in tank and the high press. frame mounted unit. Its was basicly the same design the pickups were using with the dual tank setup. Easy way to find out, just crawl under and take a peek.

Jersey said:

I have to agree with seabronc on that one. I'm 95% sure that a 90 was still using the low press. in tank and the high press. frame mounted unit. Its was basicly the same design the pickups were using with the dual tank setup. Easy way to find out, just crawl under and take a peek.

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I've got a '90... that was the year they changed over to a one pump system. Its hard to impossible to keep the dates of changes in one's head. I am continually amazed at the amount of knowledge amassed within the collective membership here. Kinda like the Borg, but friendlier eh? /emoticons/[email protected] 2x" width="20" height="20" />

joe

BroncoJoe19 said:

Kinda like the Borg, but friendlier eh? /emoticons/[email protected] 2x" width="20" height="20" />

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Oh, Joe, Joe, Joe. Do you have any idea how many guys you just lost on that one ? Their eyes are glazing over right now while they say "huh ?"

/emoticons/[email protected] 2x" width="20" height="20" />

Quick, say something trucklike & redeem yourself otherwise you might as well have just said Frack <grin>

Broncobill78 said:

Oh, Joe, Joe, Joe. Do you have any idea how many guys you just lost on that one ? Their eyes are glazing over right now while they say "huh ?"
/emoticons/[email protected] 2x" width="20" height="20" />

Quick, say something trucklike & redeem yourself otherwise you might as well have just said Frack <grin>

Click to expand...

What? you think they never heard of the Borg? They are alien supermechanics that have bumper cutters and heliarch welders installed onto their extremities. They are like Victoria Secret models for Craftsman.

Hmmm trucklike you say, how about....

truckers are in it for the loooong haul?

Hey thanks for giving me a chance to redeem myself.

Love,

joe

I've checked and rechecked. My model has only the one in-tank, high-pressure pump with nothing on the frame rail.

PonyXpress said:

I've checked and rechecked. My model has only the one in-tank, high-pressure pump with nothing on the frame rail.

Click to expand...

Hey man.. where've you been?

Yeah, you're right, you only have one pump, but the recommendations of how to trouble shoot for a bad ground, and where in the wiring that you may be losing a connection still holds true.

Have you tried running a new ground?

I see that you picked up a manual, did you get a pressure guage and pressure test the system?

My haynes manual doesn't list specific grounding points for a '90 bronc, but it does for a '92 and newer. I posted that info in another post, I will find it and repost it. IF not exactly the same, the grounding points are probably similar.

Let us know what you have done, and any findings that you came up with, and we'll try to get you running.

joe

took a look in my Haynes manual.

They list 10 separate grounds... A-J.

For '92 and newer broncos

A. Starter mounting bolt

B. Right front of Engine compartment near the battery

C. Lower left front of engine

D. Right front of engine compartment on upper radiator support.

E. Left front of engine compartment Upper radiator support

F. Bottom of cowl panel

G. Rear of left fender apron

H. Behind bottom of right cowl panel

I. Left rear corner of cargo area near rear lamp assembly

J. Under center rear of vehicle on rear cross member.

I've replaced the grounds that are directly associated with the power supply, right off the wiring harness.

A. Starter mounting bolt - replaced ground

B. Right front of Engine compartment near the battery - replaced ground

C. Lower left front of engine

D. Right front of engine compartment on upper radiator support. - replaced ground

E. Left front of engine compartment Upper radiator support - replaced ground

F. Bottom of cowl panel

G. Rear of left fender apron

H. Behind bottom of right cowl panel

I. Left rear corner of cargo area near rear lamp assembly

J. Under center rear of vehicle on rear cross member.

My wife was driving the thing when it quit. There was a raised bump in the road and when she went over it the vehicle was jarred slightly and just quit.

Thanks for the continued help.

PonyXpress said:

90 bronco no power to pump. wife was driving the thing when it quit. there was a bump in the road and when she went over it the vehicle was jarred and just quit. turn the key and it doesn't even make noise. checked inertia switch first. it was not tripped, , looked like the connector got hot. replaced a perfectly good fuel pump. replaced a fuel pump relay. low voltage to inertia switch. used code reader, got a pcm code and a pcm ground code. had pcm reconditioned, replaced fuel inertia switch, and its melted connector, new battery, battery connections tight and clean, turned the key and nothing happened. code reader still says pcm ground. have crawled all over looking for bad ground connections. can not find it. been down for over six months. any suggestions will be greatly appreciated as long as some a--hole doesn't say buy a chevy.

Click to expand...

You might want to double check all your engine to chassis ground(s)...Especially on EFI.One broken or weak ground can and usually does shut down the whole system by usually causing the good grounds to overload and overheat.I would at least try running a temporary ground from engine to body,and from -ground on the batt to engine.

While I hate to 'jack a thread out from under anyone this is actually a related question. This power-to-fuel-pump question seems to come up a lot and everyone does their best when the questions are posted but there's always some confusion about when the switch was made from the dual-pump system back to a single-pump system. I have an 88' w/dual pumps so I know at least *that* much but does anyone know what years have which fuel systems ? Thanx.

Broncobill78 said:

While I hate to 'jack a thread out from under anyone this is actually a related question. This power-to-fuel-pump question seems to come up a lot and everyone does their best when the questions are posted but there's always some confusion about when the switch was made from the dual-pump system back to a single-pump system. I have an 88' w/dual pumps so I know at least *that* much but does anyone know what years have which fuel systems ? Thanx.

Click to expand...

Dave,

I have a '90 302 with a single fuel pump. According to Haynes manual 1990 is when they went to a single pump system.

joe