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Discussion Starter · #1 ·
Hi, thanks for allowing me into your group!

I need help from experienced men that have been through the wall of fire dealing with a crank no run no fuel pressure.

It quit on the wife in traffic and when I tried to start it that evening behind a Papa Johns Pizza Joint it had no fuel pressure. It was 6 quarts low on coolant due to a plastic heater nipple broke off and has the oil pressure curse as well. I can't find a schematic for the fuel system to determine if the engine will shut down if it gets hot or has no oil pressure.

What color is the control wire to pump relay pin 85 from the computer? Tan or green with a white stripe?

Any information will be greatly appreciated.
 

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Discussion Starter · #3 ·
Thank you Differently!

May I ask another question?

I have single tank. There is no green/white wire but there is a tan wire which is the run signal to the relay.

The tan wire is pin 85 on the Fuel Pump relay and is indicated hot with the ignition key on when probed with a LED test light but it is not hot in the circuit. It appears hot because the LED test light is grounded. The computer grounds the tan wire to pin 85 which makes it hot in the circuit then pin 86 which is chassis ground completes the circuit and the relay is activated at which time pin 87 and pin 30 drop system voltage to the grey wire to the fuel pump which turns it on. Feel free to apply a brisk left right glove slap to me if I'm wrong, Biff, Bapp!

I commissioned to have the wounded old gal towed home and I prepared myself for the likely prospect that she was, as a practical matter, beyond repair and would be moved to a self service junkyard where she would die.

The year old battery was open circuit but somehow managed 3 volts when the wife cranked the living hell out of it trying to start the engine to get out of traffic while crying and screaming at me on the phone for not buying her a new car.

I changed the fuel filter, new battery, swapped in the horn relay, 5 gallons of gas, bypassed the heater, changed the oil, added 80 pounds of bars leaks and she fired right up at 60 PSI fuel pressure. I prepared for the test drive and it would not start. I had prime but not run. I tried again in an hour and it runs perfect, drove it over a hundred miles last night and it never ran better.

Did the computer need time to wake up or is there an intermittent ground, either in the computer circuit or the chassis circuit or a break in the tan trigger wire? The relay did click when it would not start so I thought that the pump wiring was suspect but the ground potential is within 1/10 volt. No noise is audible from the pump.

I need to wire up a doomsday devise in the event that the pump quits so that the wife can throw a couple of switches and get it going without the computer getting pissed off and shutting down the ignition. Any help or advise would be greatly appreciated!
 

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I would probably start by checking continuity on the green/white (in your case tan?) Wire from the pcm all the way to ground 105.
 

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Discussion Starter · #5 ·
Okay good, I assume that the tan wire connection at the PCM would be disconnected so that meter ohm current doesn't fry the computer, but I think my PCM is under the hood in the main panel in the shape of a circuit board. I have not confirmed it but was told by a mechanic that it is there and they are crap insofar as reliability goes. Wisely I have not ventured into the box other than to expose the relays. If I start to attempt to wring out the circuits I might live to regret it. Do you know how to hotwire the pump without issue? I appreciate your help Differently.
 

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Well it should be grounded at all times so I would think tapping into the grey wire off the pump you could just supply 12volts from somewhere threw a switch in the cab.
 

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Discussion Starter · #8 ·
Good idea Mr.D. What about splicing in another wire next to the tan wire? Or hotwire it to prime if the computer doesn't keep track of time but rather uses a bimetal switch that heats and breaks the circuit like a flasher? The problem is that the transmission and other devises talk to the computer. A four wheel drive might have a oil switch break that is not in the schematics, a mechanic told me it is in the circuit because it has a three wire harness. There has to be a way to disable the computer to the extent to make it home as opposed to getting stranded.
 

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Good idea Mr.D. What about splicing in another wire next to the tan wire? Or hotwire it to prime if the computer doesn't keep track of time but rather uses a bimetal switch that heats and breaks the circuit like a flasher? The problem is that the transmission and other devises talk to the computer. A four wheel drive might have a oil switch break that is not in the schematics, a mechanic told me it is in the circuit because it has a three wire harness. There has to be a way to disable the computer to the extent to make it home as opposed to getting stranded.
From my understanding the eops is more of a backup than a kill, if wired, it is wired as a FP relay bypass, if relay dies long cranks will trigger eops via pressure and then Trigger pump. Also from what I can tell the ecu doesn't care if FP relay is on, only that it triggers it. So a manual bypass should be completely feasible as long as vats wasn't involved. IE as long as security wasn't disabling truck, shouldn't be a problem... If you are worried about vats, that's by passable also...
 

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Discussion Starter · #10 ·
I read that if the security light is off when the key in on then VATS is not causing the crank no start condition.

My first pump replacement was caused by a new battery shorting out, and the current no pump pressure condition that fixed itself was caused by a 6 month old battery that went open circuit.

I was thinking about adding a second battery to buffer the circuit although the added resistance in the circuit might be an issue. I will install a volt data logger to monitor the circuit but a runway ripple might be the cause as well.

I have a 10 amp fused jumper wire. If the pump quits will pulling the relay and connecting from 30 to 87 work to get me home? Should I clip 85 to 86 as well? Thanks guys for your replies, it means a lot to me.
 

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I don't remember the pins off the top of my head but, yes if all else is fine down the line you can run from relay pins in a jumper config.
 

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Discussion Starter · #12 · (Edited)
86 is chassis ground and 85 is computer hot, 30 is always hot and 87 is hot to pump.

85 is hot to the computer but will show 0 volts on a test light to ground. Once the computer see's a green light to authorize the fuel pump to energize it grounds the circuit to it's ground since it's a ground switched circuit. Now pin 86 has potential to ground so the electromagnet pulls the normally open 30 and 87 closed and voltage from 30 goes to 87 to the pump to complete the circuit.

If I jumper 85 and 86 if the pump loses voltage and since the computer is grounded internally then I may damage the computer. But if the relay is good and the computer has grounded 85 that might indicate that an internal computer fault is causing no voltage to flow from the computer even though it's switched to do so.

Here's what I've come up with as a backup plan, feel free to correct me if I'm wrong.

If the pump quits verified by no voltage at the grey wire which is exposed under the vehicle here's what I'll do.

Jump 30 and 87 with a 10 amp fused clip. If it runs use it.

If it does not run and the grey wire has voltage then either the pump is burned out or a connection which is inaccessible closer to the tank has gone open or the computer has disabled the ignition or otherwise is not happy with me. The only recourse besides a tow truck is to jump 85 and 86 and if the computer is fried as a result, it's okay since I believe the computer circuit board located under power distribution box under the hood is a known problem.

My only other thought is to place a resistor in series with 85 and 86 since I think that the computer inputs might be in series with a stepped down transformer to 5 volts but the current transfer from the computer is stepped up to 12 volts output to the relay. Therefore it's possible that the computer is switched internally to a power distribution center running at 12 volts which grounds 85 to send 12 volts to the relay. It's likely that the fuel pump and it's potential of 10 amp draw might have damaged the computer since it might be the highest current flow of the computer.

I don't know how to safely check for a ground drop at the computer ground. My meter might send meter ohm current into the computer. I just bought a logic probe, does anyone know how to use it to look for my issue?

One more thing. I'm cutting an access hole under the seat and the run the pump hot and ground wire before the nearest connector to the cockpit. The two wires will be attached to a voltmeter for real time monitoring and a voltage data logger on a usb platform for computer graph analysis at one sample per second. If the volts rise then the pump is drawing more current or if the vehicle battery is soft shorting or otherwise the charging system is faulty then I will be able to take corrective action. Not being able to trust a vehicle is worse than not being able to trust ones wife!

Thanks again guys!
 

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Bob, 85 to 86 will blow a fuse

30 to 87 will emulate the operated relay contacts and send voltage to the pump.

But, if your just trying to get it home, just use one of the other relays. Most are the same, grab one that you don't need (horn, headlights) to get home.
 

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Bob, if this is a one time deal, I think it's overkill; but that's just me.

I've had 3 S10s, everyone of them eat fuel pumps, I'm sure I averaged at least 3 pumps per truck when I had those guys.

The thing I do remember, the pumps from the dealer were always the cheaper to buy pumps (hmmmm, maybe that was why so many failed).
 

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Discussion Starter · #16 ·
Ray, I know why the pumps fail. If you think about it, how can one pump be better than other mechanically or electrically if they last a year?

Both of my pump failures we're caused by electrical and mechanical problems.

My first pump failure was caused by a 11 month old autozone gold battery shorting out, the plates buckled causing the alternator to runaway.

My second pump was caused by a 6 month old filter that uses paper media which plugs up fast, use a Wix they still use oil filter sytle media.

The pump that is in there now is a Delphi. There are 14 gauge hot and ground wires in the pump body which turn into 16 gauge before the first connector that is located on top of the pump assembly. The 3 foot harness from the pump assembly to the body connector is 16 gauge. According to a SAE wire guide, 16 gauge wire is acceptable for up to 3 feet at 10 amps at 12 volts, right on the edge to keep the lawyers from circling for a class action lawsuit relating to pump failures.

When cranking the vehicle the line voltage drops to 10 or 11, lower if the battery or connectors are marginal. When volts drop, amps rise. Add a partially plugged filter, marginal connectors, low fuel level so the pump I asked to suck up the fuel as opposed to the weight of the fuel and gravity of a half tank of fuel, and the tiny filter sock that comes with a new pump, and it's a wonder the pumps last as long as they do.

Solution. Drill and attach 14 gauge sae wire, not the fake Chinese crap sold at parts stores, from the pump to pin 87 of the relay. Do the same with the ground wire to the nearest frame location. Under the drivers front bumper there are the chassis grounds including a 8 gauge from the factory negative battery cable. Run a 4 gauge 2 feet from the factory chassis location to the negative battery cable. The frame and body have the lowest resistance. The pump ground will travel the 5 or 6 feet through the frame to your new 4 gauge cable, or the electrons will chose another path to ground. If you add grounds too close to the factory grounds a ground loop and noise could occur.

The side post battery connector rubber shields harden over time and lose contact which is another issue. Look at the cable tits. Notice one or two of the four tits are heat discolored? Use 3/8 coarse studs epoxied into the battery and two nuts to lock them in and a good connection is achieved.

I will make a huge pump filter sock if my pump goes out again and do the rest of the aforementioned suggestions.

With the upgrades in place, the pump will get a solid connection electrical wise and less restriction fuel flow wise that it does not, cannot have in factory trim.
 

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Discussion Starter · #17 ·
The Suburban might be done, I didn't realize that the problems started at 200K minus about 140 miles. There is not just one problem, but many other problems unrelated to the fuel system which came to my attention.

My wonderful Plymouth Grand Voyager drove trouble free for almost 2 years and one day would not start. My gut at that moment was she was done but like an idiot I spent time and a 1000 dollars to try to fix the old cow only to find out she slipped a tooth and needed an engine.

I'm working on her again tonight but tomorrow I might call the junkyard if she doesn't cooperate. Again thank you very much for your help guys, but it's in her hands now.
 

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Discussion Starter · #18 ·
She broke down on my wife up the street and didn't thank goodness, restart. My 15 year old switched the ignition on and there was no prime. With the key in the on position I carefully reached up under the glove box and disturbed the PCM and the lights flickered in the instrument cluster. I reached over and started it and drove home. It stalled in the driveway and my son asked why I was smiling.

I wired up 4 meters to the battery, pins 87 and 30, and the grey wire near the pump and in 10 second intervals tested prime and run while observing the fuel pressure and my son watching the meter nearest the pump.

There was a consistent voltage drop but the amperage flow across 87 was 3.86 and 6.55 intermittently. The fuel pressure was 20 at 3.86 and 60 at 6.55. I looked at the factory ground which I had overhauled with new wire and connectors when pump number 2 was installed. The factory ground is located on a body donut ear which is welded to the frame. I exposed the ear and the weld and the welding material has a nickel lead appearance which might not be as conductive as iron. In addition, the factory grounding scheme is substandard with respect to battery to engine, engine to body, and engine to frame.

I am drilling a hole through the frame to mount the pump ground and there are now 5 number 1 and number 4 ground cables which will provide a solid ground connection to the battery. I removed and installed a new wire and connector to the computer ground behind the engine. It's not a good idea to have the computer grounded near other grounds.

The pump could be bad but I would have likely seen a voltage drop with a corresponding amperage rise as the pump soft shorted, but the voltage was steady.

When I juggled the pump my 270 pounds of pork fat was providing a ground to the grateful computer, there is not a bad connection in the harness as one would assume.

I will report my findings.
 

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Discussion Starter · #19 ·
The pump did not respond to my genius grounding scheme. The only thing left is to bypass the connectors at and around the tank and run a dedicated power and ground signal from the grey wire in the harness under the drivers door although the pins showed no signs of heat damage.

How would you guys bench test it and what is the 3 pin connector used for, thanks!
 
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