Need Help Troubleshooting a 1994 F350, I'm desperate!

[Tony396]

Ok..this one has me pulling what is left of my hair out. I know there are a ton of you out there who know more about this than I do so I am hoping someone out there can help.

1994 F350 Crew Cab Dually, 460 gas, 2wd, Auto, loaded. 168K, Ford reman motor at 120K and Trans at 125K. Very well maintained, never given me a lick of problems towing all over the country.

About two weeks ago, have cruise on doing 70 on an 80 mile trip. Starts to buck, snort, come back to power, buck, snort, backfired through the pipe, then runs well for another 20 miles. Switched tanks in the middle of the snorting and made no difference. Coast off road, sit for a minute, starts right back up. Limp to dad's.

Change module. Starts right up. Run 80 miles home, no problem.

Week later, making same trip, go all the way there with no problem. Truck sits for 3 hours while I load it. Go to start, nothing. Will crank, no light. Change module again, coil, cap, rotor, wires, plug.

Go to start, will not start...might stumble once or twice, but no start. Get pissed. Crank the ever living crap out of it and after 20 seconds, lights. Drive up and down street a few times, all is good. Turn off and on a bunch of times, all good.

Take 50 mile trek to Bridgeport area. Not one problem.

Truck sits for 20 minutes. Once again, crank, crank, crank, finally lights after 15 seconds.

Drive 100 miles home...not one missed beat.

Get up in the morning, starts right up. Go 20 miles, no snorting, but cuts completely off. Pull over, hit key, lights right up.

Truck sits for 20 minutes. Go to start, lights, goes 5 feet, dies. Starts right up again, goes 10 feet, dies.

Leave sit for 5 days. Go on vacation.

Come back, change fuel filter. Starts right up. Several times. Drive 10 miles to NES, as I am making the turn into the track...snorts, but keeps running. Pull into lot. Sit for 10 minutes, go to start, nothing. Crank for 20 seconds, nothing.

Sits all night...come out at 11, lights right up, drive 10 miles home. Restarts right up 10 minutes later.

What the hell could this be???????

Thanks in advance for your help.

Tony Pietrofitta (use to be a C/SA driver...)

[Mike Hedger]

Couple of questions, when it is acting up do you get a check engine light, have you hooked up to the computer to see if it has any codes, and have you ever replaced the pick up in the dist.? Fords trucks of those years are bad about the TPS going out and doing the same thing you are describing. The other thing is if the pickup in the dist is going bad it could cause this type of problem but I would check on the TPS first. I would only use Motorcraft parts as well. Hope this helps, Mike

[Steve Calabro]

I would also monitor the fuel pressure

[Fred Holdorf]

Just got through with a simular problem on a '90 Econoline chassis. I too shotgunned the ignition, but it turned out to be fuel system related. Changed both the low pressure pump in tank and high pressure pump on the frame rail, replaced the reservoir filter (on frame rail) and new fuel filter. All is well and I'm not getting towed in anymore. Hope yours is cheaper to fix, but think it's fuel system related. Good luck, Fred

[Rich Biebel]

My '96 GMC 454 had a somewhat similar series of problems a few years ago. Engine was stunbling and shutting off and wouldn't start and other times would run fine. I had it towed in one morning, changed the fuel filter and it was good for a few days. Engine quit again a few days later and I could restart it and go a few blocks...luckily I was near work. Pulled the fuel tank and changed the pump but bought a parts store model and had to swap some parts from the OEM unit to the parts store model. Ran ok for a day or two....than same deal. Towed in again! Put a fuel pressure gauge on it and drove it around......it was losing fuel pressure when it started to run bad. Replaced the fuel pressure regulator...no easy task on a Votec 454......didn't move 20 feet before it stalled and ran like crap again........pulled the tank again and spotted the problem!! Dirt and crap in the bottom of the fuel tank and the fuel pump filter sock had a lot of fine silt/rust type material on it causing the sock to suck closed. My old eyes never saw it the first time I pulled the tank as I put a rag over the tank opening and never really looked closey at the sock/filter. I bought a new GM pump that comes complete, cleaned out the tank and never had a problem again. Porbably got a load of dirt from a gas station that had bad pump filters. Some low priced station that's staffed by Taliban gas pumpers got me ! I change my fuel filter often after that experience...........Check your fuel pressure !

[Real Racer]

Check Tfi Module Connector.
They Have A Propencity For Loosening Up And When Not Fitting Well Will Cause Your Type Of Issues.
Heat Gun On The Connector While Pushing On It Then Tape It Tight.

[Tony396]

First up..thanks for all the help.

Here's what I found and came up with today.

I really don't think it is a fuel issue...but I don't know for sure yet.

Rock solid fuel pressure...40-42psi at idle, when key is turned, and through jumpering the pump at the test plug...Holds it for hours also when the pump isn't running. When I wind it up a bit it increases a bit, and then drops back down to 40 at the worst. If I had a clog or restriction somewhere, I don't see how it could hold that pressure, especially with 14 year old pumps.

I pulled every plug under the hood and checked for loose or dirty connections. All looks OK.

I did a resistance test on the TPS. Weird thing happened. As I opened it up, slowly and smoothly, the resistance went down, up, and then down again...which leads me to believe that it is my culprit. According to all my research and some suggestions here and other places, it should be a clean sweep on the multimeter. Ordered one today, will be here tomorrow.

Just for craps and giggles, I ordered a MAP sensor also..figuring it too is 14 years old and for $50 it's cheap insurance.

We'll see what happens.
Thanks!
Tony

[Mike Hedger]

You are correct the TPS should be steady with no glitches in it, they tend to burn where the throttle is set the most (ie highway speed) if you have access to a lab scope you can watch it even better and see if it has any spikes in the ramp on the scope. The hardest thing with a Ford and a TPS is they won't set a code till they are completely junk then the truck won't hardly run at all.

On the fuel pressure it sounds ok and if the truck runs OK when it is WOT or under a load without loosing power you should be OK, also the FP should go up when you gap the throttle or any time the FP reg. looses vacuum.

I hope you get it going and let us know how it runs. With the price of gas you can't have any big block running bad or it will run you to the poorhouse with fuel costs quick.

[Tony396]

Well, it is fixed.

I replaced the MAP and TPS sensors and it is running as it should.

Problem is, once I fixed that, it developed a massive transmission leak from the converter area. I think this thing is possessed.

Anyway, thanks for the help on this one. Onto my next problem.

Tony