My 88 runs terrible at all rpm. I have checked and cleared all codes by replacing or repairing everything from vacuum lines to TAB solenoid. I have extra parts from salavage yard to help try different parts w/o expense of new parts. I check parts by the methods listed in my Haynes man. If I spray fuel in the intake it runs line new until fuel is used. I unplug MAP and it runs great for a few seconds then starts missing. I go back and clear the MAP code. Any help with what would cause this condition? I checked fuel pressure when issue first started and it was within spec. Reg checked good too. (Both fairly new)

 

Have you changed the fuel filter? When was the last time it was tuned up (plugs, wires, cap, rotor)? Have you checked the timing?

 

Stop changing parts - you're making diagnosis harder. The ONLY part that should be swapped to check is the MAP because it's too difficult for most people to test accurately. But you have to use a KNOWN-GOOD one. For everything else, JUST TEST each thing according to the instructions in Haynes: ACT, ECT, IAT, TPS, EVP, EVR, TAB, TAD, CANP, HEGO, compression, ignition timing...

WHAT is the fuel pressure when it's running badly? How exactly did you check the regulator?

How many miles on the timing chain? Use the instructions in this caption to check its slack:


Read this & look inside the EEC:


What do the battery terminals look like?

 

I am going to recheck fuel pressures again this weekend. Yes, new filter. First thing i checked and replaced. A little more history, the truck was running great during winter. I drove it in late Feb and i thought it was missing but cleared up. 2-3 weeks later, i get in it to run it, and it was running like crap. Acted just like when the High Pressure Fuel Pump went out. Changed Filter and checked pressure (approx 3 mos ago) and pressure was in spec. So long ago, can't remember psi, but it was what Haynes manual spec'd. Timing set at 10 per spec with spout out, advances when spout is inserted to 20 (i think that is right) When i perform the test, i follow the Haynes manual instructions, but sure i screw up sometimes. I have the meter that reads Hertz to check MAP and it is testing ok. TPS checked ok. I had an EGR code, but corrected that with Salvage yard EGR (cleaned old one but would not pass) EGR Solenoid checks good. On and on it goes. Seems like its a fuel delivery problem, but i am better with pre-computer controlled vehicles.

 

Fuel pressure is 33-35 static, 30 running and 60 with return blocked. Also tested at pump at 60 psi dead head. The regulator is fairly new and the pressure drops from 35 to 30 when key off, then holds and slowly drops. Seems like 60 psi dead head pressure is low?? Also, I'm servicing the FDR since truck is down. The small o ring you suggested to drill out, is badly deformed. Also, the disk on top of diaphragm will not separate from the diaphram. Are replacement parts avail for the FDR? Thinking o ring kit might be smart? I've read the FDR can also effect fuel delivery and pressure?

 

One more quick note. This truck has been in our family since new. Has about 90k orig miles. Tune up about 10k miles ago. Plugs, wires, Dist Cap and Rotor button. I typically renew items as needed with Quality parts. BWD ignition parts etc.

 

The only fuel pressure that matters is WHILE the symptom is present.

"New" or "recent" aren't valid tests for the FPR.



It's "DFR". "FDR" was a president.
http://www.fourdoorbronco.com/board/...-Abbreviations

If the diaphragm is adhered to the top plate, just leave them together. Unless one of them is already ruined, there's no reason to risk ruining the diaphragm by trying to separate them.



AFAIK, no parts have ever been available for those reservoirs. It was only recently that the reservoirs became available as assemblies.

 

The pressures I listed are when running poorly. It does not run correctly at all. Only if i induce fuel into the intake, it will clear up for a few seconds. As for the diaphram, the Orange diaphram is stuck to both the top plate and the internal plate preventing access to the valves to check and clean. Guess I better find one at salvage yard. It has done the ole pump fuel from one tank to the other several years ago. I haven't used rear tank in some time as I know the internal pump is weak. However, I run it on the rear for short periods to keep decent fuel in the tank. That said on the pressure, is that acceptable or not.

 

In that case, you have nothing to lose by separating the plates from the diaphragm. Use a plastic scraper with a good edge. Don't expect a JY DFR to be in any better condition - either shop for a new one, or shop for the JY parts to convert the truck to the '90-96 fuel system.

The top 2 sections of this diagram don't apply to your old pumps; scroll down to the bottom 2:



The PREVious one shows the differences in the fuel systems.

 

Ok, cleaned the DFR and no change. The valves were hard to move, but are free and smooth now. Really need new o rings, but I'll have search for those since no parts are available. I am pretty sure the in tank pump's are my problem. I knew the rear was in bad shape, but I think the front has died! I do not hear any noise that would indicate it's running and I am getting voltage. I disconnected the HP pump (power) and still couldn't hear anything from tank. My question is, IF the in tank pump is not functioning, wouldn't that cause lower pressure as its putting all the work on the HP pump? I'm almost certain this is my fuel problem. Found a OEM pump for under $100. The one in the tank now is aftermarket. It say's Carter on the box, but I think it's Airtex. Been in the truck about 8-10 years. Any thoughts?

 

I'd convert to the later pump & fuel line system.