Hi Guys first of all heres the original post on this problem
https://www.ford-trucks.com/forums/9...lp-please.html

Believe me its a book and this problem is still not solved so here goes,this morning i finally replaced the ECM and G--D--- still no fuel pressure!!!. I have checked all the grounds, i have soldered in new EEC and Fuel pump relay and STI sockets, New fusible links,etc. I have 12v of power to the intank low pressure pumps and the ground is correct. Ive even used a wire from the Neg of the battery for the grounds for the intank pumps. These in tank pumps are brand NEW and have been replaced twice!! The high pressure pump on the frame works fine and the dual function reservoir is brand new. The inertia switch is new and the fuel tank selector switch is new and is getting power to both. I just find it HARD TO BELIEVE that BOTH lowpressure intank pumps have failed at the same time twice!!!! Ive used BOSCH and now AIRTEX brands for the low pressure tanks. I still get Code 95 on my code reader. The motor has spark and has been verified thru a noid tester on injector #1. The Stator is new as is the TFI module and both are motorcraft brands.

I DONOT hear either the rear or front low pressure pump tank come on when the system is charged.

heres my question:
Can i just replace this POS fuel system on this truck with High pressure INTANK pumps, bypassing the dual function reservoir and frame mounted hipressure fuel pump and hooking these pumps up to a simple on-off toggle switch inside on the dash?? Also would the fuel return lines just be connected bypassing the dual function reservoir?? or any suggestions on how to correct this problem?????

I really need your help guys as im moving in 3 weeks and really need this truck to help

BigLar

 

Hi Biglar,I have an 89 with the same drive train as yours with a very similar problem that I finally ended up taking it in to a shop that discovered an intermitent open circuit in the wireing harness between the inertia switch and the fuel pump which they solved by running a seperate wire outside the harness,don't know if this is the problem you have but as I found out anything is possible. I also went through replacing a lot of parts first also.

 

Terry thanks for the response! i have 12v going to both lowpressure intank pumps when the key is in the run position and the lowpressure pumps DONOT prime. my High pressure pump does prime for about 3 seconds which is normal. i know that i dont have fuel pressure because i have a FP gauge on the schrader valve. Oh and by the way the FP regulater is also a new kirban unit. I still need input and if youve taken the time to read my prior posts on this subject youll see that ive tried everything to solve this problem. Subford has been absolutely great on his input but still no cigar as of yet. Im hoping for some more input like yours that may really help. Thanks again

BigLar

 

What a gremlin! Personally I would try and fix the problem rather than redesigning the system. I have no idea if you can do what you suggested. I would be leery about removing the dual function reservoir for fear of a tank overflowing.

Since you have replaced every component in the system, it is most likely faulty wiring. If you have a good ground/power at the pumps and they don't operate they're bad. Both going out at the same time would tell me you do indeed have faulty wiring before the selector switch. If it were me I would start at the starter solenoid and wiggle every wire while watching a test light or analog multimeter to locate a broken wire or dead short. I personally would rewire the fusible links from the solenoid to the two relays with new wire, connectors and an inline fuse. Subford is certainly the person who could help solve this mystery. I would wait to hear from him but it can't hurt to start looking for those faulty wires.

 

Yes i agree with you about redesigning the fuel system. If i do it i would get a 38 gallon bronco tank for the back tank and just run one fuel pump. i have checked those wires from the starter solonoid to the relays and ive even taken off the firewall connector where all the wires enter the cab and checked and cleaned the crap out of them. you know with the way these auto parts are made today i wouldnt be surprised if both of those intank pumps went south at the same time!!! I only buy Motorcraft parts now. LESSON LEARNED. Ill tell you one of the things ill do is cut some windows in my bed over the fuel pumps when i remove the bed this time for easy access to testing and fuel pump removal. SubFord has helped me alot and hes a really GOOD GUY. One of the things ive done is subscribe to Alldatadiy and i have printed every wiring schematic made for this truck and placed them in plastic sleeves in a binder that i carry with me in my truck!!!. So far i havent gone far with them though ) I really appreciate your response Zorfox and yes this a total mindblower trying to figure this out. Before all this trouble started i completely rebuilt my engine ,Tranny and fuel-emission and exhaust systems. The only thing i didnt touch was the wiring harness in the engine bay and the ECM. As of right now my truck is completely brand new from the body and bed down!! and wouldnt you know this problem started after i drove only 200 miles exactly. When it ran it ran good and strong. Im just glad this problem didnt happen during the initial startup-cam breakin period!!!!! Keep those responses coming i really need your help guys! Ill bet those F----- out of country made fuel pumps have gone south! what do you guys think??

BigLar

 

Ahhh, that's a viable option. No doubt changing it over to a one tank system with the original Bronco fuel pump should work. I thought you meant you would try and install two high pressures for each tank and control each with a switch. The bronco tank is not a bad option and has been done before. You may have to ditch your spare tire but i'm not sure on that truck. My gut still tells me you have a problem before the selector switch though. Which would mean it would still be there after the modifications. The Bronco pump may handle the on/off power better but I doubt it. I'm interested to see what it ended up being. I have read in many posts that people go through more than two low pressure pumps before getting it right. What a sad day for the engineering field! But hey it is what it is I suppose.

 

Dude you were dead on with your diagnosis. I did this and all is well in NJ tonite!!!!! Much thanks for your post

BigLar

 

Thanks to you too Zorfox!!! much apprieciated and of course my buddy subford

BigLar

 

I guess multipul heads are better than one,glad to hear you got it going and thanks for the feedback.