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Rough running/Sputtering

91 Sploder

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May 29, 2015
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Year, Model & Trim Level
1991 Ford Explorer
Hello All:

I currently have a 1991 4Dr 4X4 4.0l explorer and am having issues with it. Looked thru the Elite section yesterday and did some checks based on what I read there. Here is the info:

Starts ok sometimes, runs rough, front/back fires, no throttle response, WOT bogs really bad, feather the throttle and can get it to rev up but goes to crap when I try to take off.

Manual trans

Truck sat for 2 years not being driven or started, I have other daily drivers.

Steps I have taken so far to fix/correct the issues:

1. Drained old gas and put in about 1/2 tank fresh with Sea foam.
2. Changed the fuel filter-old was clean though- precaution change since old gas and Sea foam.
3. Cleaned MAF Sensor and screen- used throttle body cleaner
4. Cleaned IAC, plunger and spring move freely, gasket is in good shape
5. Fuel pressure check- KOEO climbs to about 5-8 PSI then falls off rapidly. KOER steady at about 20-22 PSI, didn't snap the throttle.
6. Spark plugs replaced
7. Fuel Pressure Regulator- after the above step found gas in the vac line-- part will be replaced this afternoon.
8. No CEL didn't try to pull codes, cant get it running long enough to even drive it 5 miles LOL
9. reset the EEC by disconnecting the battery during the cleaning steps above.
10. Spark plugs replaced after getting it running, but old plug were clean and normal. Used NGK for cheapness since it was running bad to start with.

I am hoping that replacing the FPR does the trick but just checking here to see if any thing or step I might have missed up to this point ?

Need to get this issue fixed ASAP as I have a prospective buyer and cant sell it running like crap. :salute:

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Gas in the vacuum line is a sure sign the FPR is bad. Also fuel pressure while idling should be between 30-40psi should drop a little when throttling. Let us know if the new FPR fixes your problem. My experience seems like a couple things always go bad at the same time! hopefully its just your FPR

Thx vq5speed:

Little more info on the truck while im here:

200k plus miles, no smoke out the tail when it does run. heats up normally, slight oil leaks but hey 200k miles I would leak a bit to lol. A/C blows cold R12 system still works :)

Will follow up with a post after I R & R the FPR to update.

BTW the FPR in line is the clip on -- takes the little 2 prong tool to remove it IIRC ??


The fuel filter is inline below the driver seat area on the frame that takes a special tool to unclip it. The FPR would be located on top of the engine on the passenger side next to the valve cover and lower intake manifold.


Got the FPR off and waiting on the truck to bring the new one so I can install it, I use to work for Ford long time ago and luckily had the tool to removed the line from the FPR. Double prong clip tool made by PT Tool.

Also was able to finally get a KOEO codes

11= Fuel Injected
66= MAF voltage maximum issue

Thinking the FPR is the cause of the code 66 but going to research it just the same and do some checks incase its another follow-on issue.



FPR installed and it runs , idles and will take some throttle push.

Fuel pressure still only reading 20 PSI at Idle and throttle application-- I am thinking its a fuel pump/sock issue now , starving out for fuel as it is given throttle Tips, Advice or been there for this before I go drop another bill on it PLEASE..

Pulled vac line off FRP and no change , MAF disconnected no change, IAC disconnected idle drops way low but returns after plugging it back in.

KOEO codes after warmed up now showing 29 and 66

I tried a reman MAF and it didn't fix the 66 code and the 29 is new.

Research time(reading) and awaiting the next line of questions.

Thanks all for the input so far :)

FIXED finally:

Dropped the tank and typical of rubber in fuel for so long-- the short hose was dry rotted and cracked all over. Went to replace the hose and saw the sock was blown out as well. Started really looking over the pump assy and found all the rubber was no good -- long story short replaced the whole assy not piece by piece.

Fuel pressure= 35PSI
Code 66= GONE
Code 29= GONE

Engine runs like a champ, plenty of power and no drivability issues.

Total parts installed:
6 Plugs
Fuel Filter
FPR assy
Fuel pump assy
Starter Solenoid (fender one)
2 cans Sea foam

Thx for the input and hope this information might help others at some point.


Thanks for getting back with the solution(s), it helps everyone. I try to read all of the threads since both of our Gen1's have well over 200k and I do everything that I'm comfortable doing (and of course have the tools to do properly).