Hey all!

I just got a 94 F-150 XLT. Beautiful truck, and a far cry from my ol firebird.

It has a 302, 4 speed auto, 158,000kms. No rust, looks good.

Now, here is my issue.

As I drive the truck on level ground, doing any constant speed (30kmph - 120 kmph) the truck will suddenly lose power, like the tranny or the engine is not producing any power at all, then I get a "check engine" light then after about 45 seconds or so, without moving my foot at all, the truck lurches back to life, by this time, the check engine light has gone away. During the loss of power, the engine will run rough. It also idles a little rough, but not all the time.

I can usually fix this if I stomp on the gas. then it lurches into passing gear and off it goes.

I suspect I might be dealing with a vacuum leak as the tranny shifts up and down just fine otherwise. Tranny fluid is nice and red. Aside from new plugs, wires, distributor work and such normally expected with a used truck this old, is there anything else I might be missing?

I would love to know where the more common vacuum leaks come from on these engines.

I am getting a code reader today and I am calling the dealership back as well. I know it would be easier to diagnose with the error codes.

Any suggestions?

Thanks!

Chris

 

Take a vacuum gauge and tee into the upper intake manifold to check your vacuum. A good steady needle between about 17 and 22" hg would indicate a sound engine. As long as the needle is not erratic(quivering) or sweeping narrowly or widely I would not think you have any major internal problems. You could have a TPS (Throttle Position Sensor) acting up. There are test procedures in some post on here for that.
The vacuum lines are generally made of plastic and over time can become brittle and possible split or break. The upper intake manifold gasket can leak sometimes also. Generally with a vacuum leak I think you would see your idle rpm's increase, depending on the size of the leak.
I've had the vaccuum line come off the bottom of the air bypass valve and idle went to 1100 rpm and an upper intake gasket leak(major) and the idle went to 2200 rpm's. Report back if you read your codes and that might help. You can get a procedure at http://fordfuelinjection.com to read codes without a reader. Other good info on that site as well. Keep us aprised of any developments.



guzzler96

 

I had the same issue and it turned out to be a bad TPS, even though it tested fine.

 

Around the intake gasket and plenum are the most common places for an intake leak to develop. Here's a real easy way to determine if you have a leak. Take a can of brake cleaner/carb cleaner (anything flammable), and spray it around anywhere that a leak could be. If the engine picks up and runs smoothly, you've found your problem. See, the engine will suck that stuff up and run on it if you have a leak. If you don't, you're only out a bit of cleaner.

Trevor

 

Hey thanks so much for all the help.

No signs of lthe vacuum leak based on the information you guys gave.

I took the truck back to the dealership who sent me to their mechanic.

Seems this truck has been on someone's back burner for a very long time.

Most of it was normal PM on the truck. Thing is I didn't want to touch it since I just got it a day ago and the dealership might point the finger at me if they know I did anything at all to the truck.

Mechanic took it for a drive with me and said it seems to be starving for fuel. The bog down would come and go at almost regular intervals, then backfire (Which is the clunk I heard)

Some of the things we did.

New fuel filter (Old one was clogged solid)
New plugs (Old ones had lots of rust on them and some were not even tight)
New plug wires
New rotor (cap was fine but rotor was almost completely shot)
New Oxygen sensor (Old one seems to have been there since time began)
New air filter (Old one was completely clogged)

No codes stored in the computer.

Judging by what I have seen so far, the oil change I am going to do tomarrow should be eventful. The transmission should probably be serviced as well.

So my current status...

Check engine light is gone
Truck runs so much better

Current problem...

Low rumbling sound from which is audiable from the transmission, seems to come up around 60-80kmph. Still boggy when trying to maintain higher speeds as well. I suppose it could be echoing from another place. Could be U-Joints, tranny, engine, or rear end.

I get to check that too.

Thanks again everyone!

BTW I know my string has changed focus, sorry bout that one.