I recently acquired a '93 F150, 4.9L, A/T. The previous owner had replaced the fuel pressure regulator, fuel filter and fuel pump relay.

Problem: Won't start on its own, but will with starting fluid. Idles rough and doesn't take fuel well. If it were a V8 I'd suspect it had jumped cam timing, but I don't think it's even possible with this configuration.

It doesn't appear to have been well maintained at all - I'm reasonably sure the O2 sensor hasn't been changed & it has 181,xxx miles on it. Possibly the cat is plugged from running rich? Or might this be an ignition module problem?

I'm more into Mopar & not very well versed on Fords - Somebody . . . ANYBODY . . . Please help!

 

have you pulled the plugs? they will be able to tell you quite a bit.

 

You are correct. The 4.9L is a gear-to-gear timing arrangement. It's a very well respected engine for its durability and long-life.

x2 for checking the plugs. Not only does this give you an idea of what may be going on, but fouled plugs, even one, can cause the engine to run badly. Had an occasion where a piece of crud wedged in the plug gap, engine rocked so hard, it seemed to want to come out of the engine bay.

Suggest to pull any computer codes - may help give better direction, or at least get another opinion (the computer's) on what is going on.

Suggest to first go for verifying fuel pressure and quality, and presence of good spark.

The fuel system should be investigated further for two reasons - first, to understand what the previous owner was chasing after, and second, to verify that the changes made did not introduce any new problems. May be worth your while to check the fuel rail pressure - IIRC should be in the 25-40psi range.

Cat? Maybe, can loosen the headpipe from the exhaust manifold or otherwise take the cat out of the loop. Generally, I would think that a restricted cat would allow the engine to start, just not be able to run the RPMs up very high - unless the cat is stowed up, blocked solid.

Ignition module? Also, maybe, but check the other things first.

O2 sensor? This may bear investigation further down the road, but it shouldn't keep the engine from starting. Computer should throw a code for this.

If you've used a lot of starting fluid and raw gas down the intake, consider changing the oil when this issue is resolved. I suspect a lot of this will have made its way to the crankcase.

 

Changed plugs, cap, rotor, wires & ignition module. will crank & idles better - still not taking fuel very well, but better than before. burning VERY rich. fuel pressure from front tank is 48 psi, rear tank 56 psi. scanner can't pull codes. manual for scanner refers me to owners manual & "troubleshooting - no codes present" but I can't find that in Haynes or Chiltons. Haynes mentions FMEM, failsafe mode and HSOL failsafe when FMEM won't work. How to reset? Thanks for all advice.

 

You have certainly been busy to get all that done!

from http://www.autozone.com/az/cds/en_us...rInfoPages.htm

FMEM - Failure Mode Effects Management. A sensor is outside the calibration limits and the PCM is using default numbers.

HLOS - Hardware Limited Operation Strategy. Used when a fault is too extreme for FMEM mode to handle. All software operations have stopped. Diagnostic test codes will not be output.

The 'Check Engine' lamp should be on for either case.

Can disconnect the battery for about 20min to reset the computer. However, if the problem that caused the fault hasn't been corrected, the engine will go right back into one of the failsafe modes.

Suggest to investigate the fuel pressure further - there's certainly plenty of it. Probably putting in 10-20% more fuel than would be expected for normal pressures. The computer probably has limits on how narrow the pulse can be for the injector firing, so it may be at a limit on how far it can dial down the fuel??

Perhaps a problem with the fuel regulator on the rail, its control circuit, or a plugged / pinched return line - maybe in a section that is common to both tanks since the high pressure is seen on both.

Sounds like you're making progress. This looks to be a multiple problem situation where one has to knock out one issue at a time and see where that leaves things.

Thanks for the update and keep us posted on what you find.

 

Got dark on me so I disconnected the battery - I'll do it all over tomorrow.

Since it's obviously in HLOS mode, I suppose the first thing I should do is put a timing light on it. Next thing will be to bypass the cat.

The fuel pressure I mentioned is at the Schrader valve - before the regulator. I see no way to test the pressure on the injector side of the regulator.

Thanks. Dan

 

The regulator is at the outlet side of the fuel rail, connecting to the return line. The pressure measured at the Schrader valve should be the fuel rail & injector supply pressure.

 

Well now I'm thoroughly confused. My book says pressure at the Schrader valve should be between 50 & 60 psi. That the regulator reduces this pressure to 39-40 at normal operating conditions and to 30 psi at idle and hi vacuum. If this valve is on the downstream side of the regulator, why then, would the pressure be different between front and rear tanks?

Also, the fuel pumps (front and rear) never shut off. My GMC and my Dodge both run briefly when the key is turned to the on position, then shut off. These run constantly with KOEO. Is this normal with Fords? I can hear fuel being returned to the tank.

Thanks again for all your help while I try to figure this out.

BTW - love them 'throwed rolls'!

 

Another question - where, exactly, are the O2 sensors in the manifolds? I can't see 'em; can't feel 'em - but I know they're there somewhere . . .

 

??? hmm, I was thinking about the setup on mine - IIRC, there is a Schrader valve test port right on the fuel rail.

Just to clarify - what I'm calling a Schrader valve resembles a valve stem on a tire - for measuring pressure and adding fuel injector cleaner directly to the fuel rail.

Certainly follow the book's guidelines - my memory ain't what it used to be. :-) If there is a test port on your fuel rail, it would be interesting to know what its pressure is while running.

At the risk of passing along another bum steer - the fuel pumps should run for about 2 seconds when the ignition is turned to key on engine off. Now this I know happens, at least on mine.

Not sure if the in-tank low pressure pumps were still being used in addition to the common high pressure pump along the frame rail for your vintage - if so, the difference between the low pressure pumps in performance capabilities (wear&tear), the relative tank levels, or a quirk in the tank selector could be reasons for the pressure difference.

I apologize for the confusion.

And yes, those throwed rolls are something. It amazes me how far people travel out of their way just to eat there. The restaurant even offers a taxi service from the local airport for those that fly in for the sole purpose of eating there.