Reader Question: Balky Five-Oh?

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Here’s the latest reader question, along with my reply!

Bill asks: I’ve got a weird one I hope you can shed some light on. My ’92 Mustang GT 5.0 (5 speed stick) wouldn’t start a few weeks ago. Cranked but wouldn’t fire, which seemed to be fuel to me. After a bit it did start, and then drove fine.

Without droning on too much it’s happened several times, but only when it’s been sitting about an hour. Never in the morning, never after a 10 minute run-in-the-store stop.

Always around an hour. The check engine light came on so I had a mechanic pull the code. He said it was the fuel pump relay, so I replaced that. I also checked and replaced the somewhat corroded distributor cap, wires, and plugs. Then it did it again. It’s stuttered once on me while driving, but otherwise runs well when it’s running. I figure it’s gotta be the fuel pump, but can’t for the life of me figure why it only seems to happen after sitting for about an hour. I also wonder why there’s no code for a failing pump. I’m at best an old-school shade tree mechanic who no longer has shade or a tree, and am very limited in funds. Any suggestions?

My reply: I agree with your old-school instincts; I suspect the fuel pump is your problem – and for the following reasons:

First, the symptoms. The pump gets hot (bet your fuel tank isn’t full – the fuel would help cool the pump), stops working; you sit for awhile – it cools down – and works again, presto!

Second, the age – your car (and fuel pump) are 27 years old; that is well beyond the reasonable service life of the factory fuel pump, especially given the higher ethanol content of fuels today vs. what was typical circa the early ’90s.

The pump itself should not be expensive but the labor might be if the tank has to be dropped to get at it. However, it’s not a technically difficult job for the DIY/shade-tree mechanic. Have you got a floor jack, 2x4s and a basic socket set? That’s really all you ought to need to lower the tank. Once that’s done, replacing the pump is as easy as changing spark plugs.

There are lots of Mustang people here, too – and I expect  several will chime in with some specific tips that will be helpful.

And here’s one, from me: With any car that has an electric pump in the tank, try to avoid running the tank to near empty; try to keep it at least a third full most of the time. The pump is cooled (per above)  by the fuel and running the tank to nearly empty will tend to shorten the service life of the pump.

Also, try keying the ignition to run – but wait a couple of seconds before cranking. This will let the tired old pump prime the system; it sometimes helps get a car with a tired old pump operational.

. . .

Got a question about cars – or anything else? Click on the “ask Eric” link and send ’em in!

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  1. Follow 8SM advice above and replace the fuel filter (inline on the frame somewhere?) while you are at it. You should do that every so often anyway to protect the injection system. Or sometimes they are just part of the damn fuel pump and you have to do everything at once // bang head.

    On that age of car, the hardest part of dropping the gas tank to get at the fuel pump will probably be getting the damn fuel filler hose off of the tank neck!

    • Correct NOOO. I had that happen years ago. Filled up the tank then the pump quit. Had to saw off the line from the tank fill to the pump and replace the hose. Those hoses get hard after a while and glued onto the tank fitting. Also damaged the filler neck while trying to siphon the full tank of petrol.

      Might also be a crank position sensor. Had that happen too. Poured hot water over the top of the sensor and the car started right up. Both of these issues were on a GM car.

  2. Eric from the South Main Auto channel on YT diagnosed a very similar sounding issue to this – bad injectors. They were fine when cold, but as soon as they got heatsoaked the vehicle would fail to restart

  3. I agree with everything eric said but will throw in another possibility, the fuel filter.

    The z71 began a strange sort of missing at the gate last week then ran fine for a few miles then did that same missing, again at the gate. By the time it was down the driveway a bit it quit missi.

    Next day it did the same thing only this time it was way down on power but after several miles seemed to recover. Did the same thing 30 miles further after it sat for half an hour but began being down on power a while later.

    I tried to envision what could cause erratic stuff like that and had visions of some complicated ignition problem since it has a coil for every cylinder and what could cause a miss before the coils is beyond my keen.

    Then I thought of the myriad problems with port fuel injection. Then the wife would ask questions I really didn’t want to hear or contemplate. She wanted to make a 140 mile round trip the next day going from one big box store to another, hardware stores and other places. I had quash that since othe thought of a huge tow bill made my stomach churn.

    Next day I drove 30 miles with low power and got a new air filter and fuel filter. I had to stop by Wally where it got rough again
    Bought a 4 pack of Heet, put in 2 bottles and topped it off with Alon fuel and drove home, replaced the air aand fuel filter, loaded up CJ and tore off without any problems. On the dirt road it was fine and pavement let me run it up to 75 with a good bit of throttle and it felt regular so turned and gassed it hard through the gears to which it felt fine and ran smoothly at the gate, idling in gear. I had blown out the air cleaner right after it started messing up so didn’t think that was the problem but knew it COULD BE. I’ve been in countless dirt storms where less than an hour of driving would have a new air filter completely stopped up and kill the engine.

    Probably everyone here would have had a good laugh listening to my rant a couple days before about overly complicated bullshit on everything made after 98 and to a great deal after 94. I clearly remember saying IF THIS WAS A TBI 350 I WOULD KNOW EVERYTHING ABOUT IT BUT THIS SOB has sensors that monitor sensors.

    I know where a 79 one ton light duty crew cab is sitting with a 454 and think the owner would sell it. Not one damn thing on it I don’t know how to fix or trouble shoot and have every tool…in multiples, to do so. Gear pullers of all sorts, specialty axle tools and brake tools. Holley or Qjet, I can rebuild it in my sleep. As my best friend’s tongue tied uncle would have said “Doddammit”. Tell em Uncle George.

  4. Thanks for your help, Eric! It’s good to know my old instincts haven’t entirely abandoned me. Also good to have some of it cleared up for me. I’m casting around now for a new pump. Wish me luck!


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