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Another "Why Won't it Start?"... '91 HO, 4.0L


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I've got a '91 HO, 4.0L. Starting just yesterday, it'll crank and crank and crank and not start. However, it will start if you hold the gas to the floor and keep cranking. When doind that, it'll start a little rough then seem to run just fine. I was hoping for something dumb like the fuel filter, but after changing that and the spark plugs it's still doing it. Any ideas from the greats? Thanks dudes!

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Just a shot in the dark here, but in SOME fuel injected vehicles, holding the gas pedal at WOT will clear a flooded engine signal. Fuel pressure regulator?

-E.

 

I thought about that too but figured that the truck wasn't smart enough for that. Can anyone confirm?

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On my 88 ,whihc may be a bit different than yours due to mines part AMC & part Chrystler , but mine periodically will crank & crank & crank & crank but not start, so I get out, slide underneath the drivers floor under it, & find the TPS wire that runs quite close to the exhaust pipe/manifold .one single wire.......and i wiggled that & then it fires up like normal ...aftre this happening 5 different times, I used one hand (cuz thats all i can fit in that tight of an area) & pressed the connecter together rather firmly to be sure its getting good connnection............ and so far It hasnt crank crank cranked in over a week, So Far ....

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On my 88 ,whihc may be a bit different than yours due to mines part AMC & part Chrystler , but mine periodically will crank & crank & crank & crank but not start, so I get out, slide underneath the drivers floor under it, & find the TPS wire that runs quite close to the exhaust pipe/manifold .one single wire.......and i wiggled that & then it fires up like normal ...aftre this happening 5 different times, I used one hand (cuz thats all i can fit in that tight of an area) & pressed the connecter together rather firmly to be sure its getting good connnection............ and so far It hasnt crank crank cranked in over a week, So Far ....

 

CORRECTION: NOT the TPS but i meant to say the CPS (crankshaft positioning sensor)

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Suggest measuring fuel pressure at the rail when this happens.

 

Another thought that comes to mind, and I don't 'know if the

PCM is this smart, but I wonder if the TPS at WOT tells PCM

to pulse the injectors longer/wider - which cause me to wonder

if injectors need attention. If you have a nearby shop that can

flow test them, it would be interesting to see how they behave.

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It sounds like a fuel delivery problem. Concur it's pressure gauge time, but would also disconnect the supply line from the rail and do a fuel pump volume check. It's just a test of how much fuel the pump delivers into a container vs. time; if you need the specs I can look it up in the FSM. Also check wiring connections at the fuel pump and ballast resistor for corrosion, measure the pump supplied voltage, and clean up the ground under the left tail lamp. :cheers:

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Started with the simple stuff... I checked the resistor and, sure enough, the connections were in bad shape. One had a big crack in it and the other had much of the bare wire exposed. The ground behind the taillight was in good shape as was the connections going to the pump. The ground on the pump housing looked okay as well. Fingers crossed anyhow. Thanks for the help!

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Started with the simple stuff... Fingers crossed anyhow.

 

Nope. Failed the leak down test. Numbers now pointing towards the fuel pump. You'd think that since it's the same pump as an XJ that any auto parts store would have one on the shelf... man, I miss living in a bigger town sometimes. :fs1:

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alot of time when it fails leak down it is just the hose in the tank that connects the pump to the sending unit

 

I agree and I checked on that. I recently had the pump out of the tank and replaced it then. I'll be waiting on getting a pump until Tuesday. As far as I can see, everything else looks fine.

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:thumbsup: Which pump did you go with Ben?

 

I went with the Delphi unit (part #DFP FE0108) from Napa and a new strainer for in the tank. I've used Delphi for just about every pump that I've put in anything with good results. Thanks for everyone's help again! comanche.gif

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