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87 f150 302 backfire? out of intake

A buddy just borrowed my truck and got about 2 blocks away when the truck lost all power. We took a look under the hood and when it is given any gas the airfilter box starts jumping up and down and a popping sound comes from the engine. It will drive but only at a walking speed. Restricted exhaust? stuck valve? I checked the plug wires and other easy things and everything appears to plugged in.


Maybe timing chain/timing gears?

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Could be the timing chain jumped a tooth or two. Has the timing chain ever been replaced? How many miles on the truck.

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You might do some net searching on how to pull the diagnostic codes.

It’s at least possible this could be related to the ignition module; the infamous TFI-IV. Maybe the module has lost the SPOUT signal and the timing is running way retarded.

You know how the odo’s are on these trucks more than 100 thousand is all I can say. I will look at the tfi-iv stuff my buddy has a code reader. Could it just be a loose plug of the ignition module?

Jumped time is the first thing that comes to mind for me also. Ford 302 engines with the laminated chains and plastic cam gears were notorious for jumping

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the plastic cam gears are horrible!

I don’t think a code reader will work on this truck. This truck doesn’t have a 16-pin dlc under the dash

I’m not an expert on these older Fords, but I think the procedure might involve a paper clip and a test light, and counting blinks. You should google the procedure, I’m sure there’s somebody who’s posted it, or maybe even a youtube video

Here’s how to pull the DTC’s from your Ford OBDI computer.

But to check for a possible failed timing chain, remove the distributor cap.

Have someone get on the crank bolt with a breaker bar/socket and turn the engine in the normal direction while watching the rotor in the distributor.

Now have that person rotate the engine in the opposite direction while watching the rotor in the distributor.

If the crankshaft can be rotated more than just a couple of degrees before the rotor in the distributor begins to rotate, the timing chain is stretched.

If you want to check if the plastic teeth on the cam gear has come apart, drain the oil, and inspect the oil for any pieces of plastic.


I pulled the cap and the did best I could marking the #1 position on the air plenum behind the cap and cranked it to top dead and it is pointing at it. How exactly should it be pointed? it may be just a hair past it or at least the rotor arm is. The contact on the end would definitely hit the plug stud thingy.
I will try testers method to check for chain slack but would that make it lose time if it stretched just a hair more?
I’m tempted to try and reset the timing just for fun.


If the timing chain stretches/jumps time, the valve/ignition timing will be off.

Here’s an example of a stretched timing chain.


Resetting the timing won’t do any good, the problem is the chain is loose, timing will move all over because of that. If it’s the chain, that is.

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I used a string to measure the diameter of the balancer and got 20 inches then marked it spun ot cak till the rotor moved with a difference of 1/2 inch which is 9 degrees according to my calcs. So this is worn but not so bad I guess? Would this be bad enough to cause a tooth jump. Just nervous to jump to a conclusion tear it apart and realize this isn’t the problem. I guess this would retard the timing by 4.5 degrees?

If you’re able to rotate the crank 9 degrees before the rotor starts to rotate, the timing chain is severely stretched, and may have jumped time.

Besides, if a timing chain is stretched that much, it’s replaced.


Awesome thanks i just needed a pat on the head for confidence.

I have had several high mileage trucks with 10 degrees of back and forth play in the timing chain, really no noticeable improvement in performance after replacement.

If you want to know if the chain has slipped, check the distributor rotor position with the crankshaft at TDC as you have done, sounds like the cam timing is OK.

Run a compression check to test for jumped time before dismantling anything.

My buddy has a leak down tester would this work instead of a compression test? I will do one or the other this week and come back with some results

I don’t think a leak down test would give much insight into the situation unless done while rotating the crankshaft from BDC to TDC while monitoring a degree wheel.

A lean condition can cause puffing out the intake. How’s the fuel pressure?