Engine will not continue when starting

[Manche757]

89Mj, 4.0, 5 speed manual. First time this ever happened.  Has been running fine. Came out of grocery store. Engine starts right away and dies smoothly; no sputtering.  Starts again easily. Engine zooms but tapers out. Same over and over. Gas tank slightly less than 1/2 tank. Any guess?

[Ωhm]

Bypass the fuel pump ballast resistor.

 

@cruiser54

[Manche757]

5 minutes ago, Ωhm said:

Bypass the fuel pump ballast resistor.

@cruiser54

Pull both wires loose and connect them?

[Manche757]

Well, that worked. Before god and the world I would never have figured that out. Happened in front of O'Reilly.  They don't carry it. Probably too old. Where should I get one?

[Ωhm]

Glad it worked for you. You can get them at a lot of places, I would think. Some will say just leave it bypassed, myself, pick one up and remember your symptom. 

[Manche757]

Yes, it worked. Thanks Ohm. It saved me from walking home and calling a tow truck in the morning.

 

Anyone know where to get the resistor?

[Eagle]

Rock Auto

 

https://www.rockauto.com/en/moreinfo.php?pk=8744632&pt=7052&jsn=891

 

[Minuit]

Won't hurt a thing to leave it bypassed, unless your fuel pump is noisy enough to bother you.

[Pete M]

yup, 87 4.0s didn't have it.  it was added in 88 to quiet the pump. (and retrofitted into some 87s)

[Manche757]

Ordered from Rock Auto as pointed out by the Pres of the LIMJPS, aka Eagle.  $12.92 plus shipping and tax. $17.68 total.  6 day ETA.

 

CC at its best.  Accurate, quick and efficient help.  

 

Thanks

[Manche757]

I installed the Rock Auto part. Engine will start and run at half throttle but cuts off at idle.  Wrong sized replacement resistor?

[Manche757]

Part gets hot quickly 

[gogmorgo]

Does it have a resistance value stamped into it? Or can you take an ohm reading? I think the original was supposed to be something like 1.1 or 1.5 amp. I can maybe investigate in the morning if no one else knows the value.

It getting super hot makes me think there’s something weird about it. 

[Ωhm]

On 9/16/2022 at 9:20 AM, Manche757 said:

Engine will start and run at half throttle but cuts off at idle.

 

How does the engine start and run when the "NEW" resistor is bypassed?

[cruiser54]

Ditch that POS and do a clean job of wiring the connectors.

 

That resistor was there ONLY because of customer complaints regarding fuel pump noise. That's it. 

[Manche757]

15 hours ago, gogmorgo said:

Does it have a resistance value stamped into it? Or can you take an ohm reading? I think the original was supposed to be something like 1.1 or 1.5 amp. I can maybe investigate in the morning if no one else knows the value.

It getting super hot makes me think there’s something weird about it. 

1.1 with the ohm symbol is imprinted on the old one.  And a string of numbers that I assume are serial numbers.  There is no marking at all on the new one.  I ordered the one that Eagle's link above shows.  The box does not indicate an OHM rating.  The box shows the part to be RU38 made by Standard.  I went to their site, standardbrand. com.

It does not give a rating either but lists it as an "ignition coil resistor".  Wrong part maybe? 

https://www.standardbrand.com/en/ecatalog?part=RU-38 - Ignition Coil Resistor&type=p

I went to "CHECK YOUR FIT" and it states that it does not fit an 89 Comanche with 4.0,  

 

 I Googled what a fuel pump resistor does.  I did not find anything MJ specific but there are comments about dropping the voltage from 12amp to 10amps.. That would generate heat of course which the part is intended to dissipate.   

[Manche757]

2 hours ago, Ωhm said:

 

How does the engine start and run when the "NEW" resistor is bypassed?

It starts and will continue if given gas but if it will not idle and shuts off.  Multiple tries and it does the samething.

[Manche757]

2 hours ago, cruiser54 said:

Ditch that POS and do a clean job of wiring the connectors.

I read that and thought what is the gentleman from Prescott throwing at me with POS?   Power Operating System?  WTF does he mean?  Ah hah! An expansive sense of humor coming from the rattlesnake state.

[cruiser54]

Gotta love acronyms, eh?

[Eagle]

16 hours ago, Manche757 said:

I Googled what a fuel pump resistor does.  I did not find anything MJ specific but there are comments about dropping the voltage from 12amp to 10amps.. That would generate heat of course which the part is intended to dissipate.   

 

Volts, not amps.

 

Quote

It starts and will continue if given gas but if it will not idle and shuts off.  Multiple tries and it does the samething.

 

If it behaves the same whether the resistor is in the circuit or bypassed, then the problem obviously isn't the resistor. It could be a dirty throttle body, it could be a bad idle air controller -- or it could be something else.

[Manche757]

39 minutes ago, Eagle said:

 

Volts, not amps.

 

 

If it behaves the same whether the resistor is in the circuit or bypassed, then the problem obviously isn't the resistor. It could be a dirty throttle body, it could be a bad idle air controller -- or it could be something else.

Yes, volts, not amps.

 

The engine runs as it should when bypassed.  Apparently the part is not correct and the correct one is not available. Bypass wins.

[cruiser54]

Hmmmm. what to do.....

[Eagle]

On 9/18/2022 at 6:53 AM, Manche757 said:

The engine runs as it should when bypassed.  Apparently the part is not correct and the correct one is not available. Bypass wins.

 

That's the opposite of what you said above.

 

Agree - just bypass the resistor and move on.