Ok, here we go.

I really need the experts help on this one. Let me start with a little backround. I have a 1987 F-150 with the 300 I-6 MFI (great engine!) 188,000 miles, burns no oil, leaks a quart every 3k from rear main seal, no leaks otherwise, runs decent with a few exceptions (I will explain later), It has a NP435 4-speed trans, but need new release and pilot bearing. In the last 3 months, I have done (or had done) the following: New time gear set (with metal gearset not Nylon!), new spark plugs, wires, distributer, coil tested OK, new exhaust from the cat back. I know that the pre-converter is shot to hell and makes a hell of a racket under load, new belt and tensioner. Other things you may want to know: smog pump still working and not squeling, I have not done the EGR modification yet, (but considering it). I use only motorcraft filters and 10w30 valvoline and STP oil treatment.

This is not a vehicle that sits, daily driver. 30 miles a day or more.

Hope fully that will give enough info to keep the guessing more educated. (LOL) Oh! I remembered something else, NO CHECK ENGINE LIGHT, (works, No codes I mean).

Now that I have thourghly bored everyone reading this, I will give you the problem.

I will give you every symtom i experience. There may be more than one thing wrong. As the title said, I have a intermintent rattle, It is engine speed dependent when it happens, sometimes load dependent. It is not speed sensitive. Most of the time I get the rattle on the highway after climbing a long grade, or hard on the gas for an extended time. Here's the kicker, after I level my lead foot out it it gets louder, I let off completly it goes away, WOT goes away..

NOW FOR THE WEIRD PART.

After crusing at one speed for 5 -8 minutes, the rattle (clatter maybe better description) goes away instantly and completely, but I noticed when it did that, that i had to give it a little more gas to keep cruising the same speed. I could feel the change happen when it went quiet.

I, for the life of me, can't explain it. Maybe this forum can.


Truck never seems to lose much power or MPG's just very NOISY sometimes.

 

sound like the TFI module. to me. or even a lose distrubutor.

 

Whats a TFI module?

 

Hi,

Do you know what the engines indicated oil pressure is when this happens ? From what I understand, what your hearing is the valve noise, and the engine may be starving for oil.
It might be possible that the oil pump pickup is clogged.

 

I have not connected a true oil pressure gauge to the engine, but the oil pres gauge does go up and down with engine speed and starts higher when cold and lowers some when the oil warms up and at operating temp. It seems to get oil just fine, no funny startup noises and lifters pump right up, like I have seen written in other posts. The gauge needle points between the 'R' and the 'M' of NORMAL when it's a cold start, then after warm it reads between the 'N' and 'O' at Idle and 'O' and 'R' Off idle. (maybe I should get a real gauge!)

 

The answer to Incommunicado's question is nothing. Nothing happens to the oil pressure at that point. that I can see on the gaugeany way. It stays where it normally rides when warmed up.

 

I think pfogle may be on to something, I read in my Haynes manual where if the PIP sensor or the tfi module does not send a timing signal to the EECM, timing reverts to base timing and stays there, other word no advance. That may cause the rattle as the timing is not moved, I'm going to look for bad connections at the TFI and at the EEC connection. then go from there.

 

Thick Film Integrated ignition module. On '84-91 EFI, it's on the base of the distributor and there's a class-action law suit against Ford because of heat-related failure. On '92-96, it's on the L inner fender under the hood hinge mounted in an aluminum heat sink.

 

From the Class action lawsuit that was settled by ford,

'In the Related Actions, the plaintiffs allege that Ford knew, but concealed from the public and from government officials, information that its TFI-IV module—which is an ignition-system component that Ford installed on the distributors of class vehicles—had an inordinately high propensity for failure due to overheating. The plaintiffs allege that TFI module failure is more likely to occur in conditions that cause the TFI module to become overheated, such as in hot weather and while the vehicle’s engine is under load (such as while towing or while driving up a grade) or while idling for extended periods. The plaintiffs also allege that TFI module failure frequently occurs on an intermittent basis; that is, the module will fail while hot, and then recover and continue functioning after it cools. In addition, the plaintiffs allege that if a TFI-IV module fails, the engine of the vehicle can stall suddenly and unexpectedly, even while traveling on the roadway, thereby creating an unreasonable risk to motor vehicle safety.'