I'm having a few issues with my 89 F150 4.9 str 6 ( Single Tank). The truck has a serious missfire. It has gradually got worse. At first I thought it is was a fuel issue, I replaced both filters, pressure regulator and everything checked out. I had the trucks computer hooked up and there were no issues. Replaced all the vacum hoses and had the electronic parts of the fule delivery system checked.The truck idles fine but when you put it under any load it missfires. You go up through the gears it continues to miss until you hit around 60 mph. Then it almost goes away. This made me think it was a timing issue. So off I go and buy a timmng light, along with new leads,cap, plugs, air filter and a rotor arm. Ater replacing all the parts I set about checking the timing. The truck fired right up and ran super smooth at idle. I hooked up the light and found that I could not see the mark for #1. Odd! I hooked it up to #2 and there is was... Somethings wrong!! I took #1 plug out and found TDC on the comp stroke and noticed the rotor arm was nearly 3/4" off of the caps tower #1. This is about where my knowlledge and skills end. Has something slipped? Worn out? I adjusted the timing by ear and it improved but them suddenly it got even worse! It's driving me bonkers!!! Help!!!

 

Either the timing has slipped or the distributor has been removed and installed wrong.

You say you found TDC for #1 by feeling for compression. If that's the case, the timing marks should line up. If they don't, the timing has slipped. You'll need to pull the timing cover and fix the timing (and quite likely replace the timing chain).

Then you'll more than likely need to remove and reinstall the distributor to get it to point to #1 properly.

 

Eh, IIRC, the 300 timing is gear-to-gear.

Was the SPOUT connector pulled when checking the timing? Should be near the distributor - looks like a connector with nothing connected. Pull the 'dummy' shorting plug out of the connector - this removes any computer timing adjustments, leaving base timing.

The firing order is 1-5-3-6-2-4 with clockwise rotation, so for you to find the timing mark at the #2 cylinder suggests to me that your timing is about 120 crankshaft degrees / 60 camshaft degrees late, since the timing mark should be in position for the #1 and the #6 cylinders, with 3 cylinders firing per 360 degrees of crankshaft revolution and 180 degrees of camshaft revolution.

If all else fails, suggest to verify the plug wiring is going to the correct plug. As you've probably found, most caps have a molded '1' where the #1 wire goes, then just follow things around the 'clock'.

As was pointed out, the distributor may have been removed and reinstalled incorrectly. Removing and re-aligning is the proper way to correct, however, one can 'cheat' a bit by rotating all of the wires 1 or more posts if that gets you in the range where the remaining error can be dialed out by rotating the distributor assembly, as normal.

If the gears have jumped once, they are likely to jump again - in any case, there is no way to fix this without pulling the timing cover off for inspection and likely replacement.

If you purchased a bargain brand of wires, you may have a bad one out of the box - adding another degree of difficulty to the mix.

Good luck, and keep us posted!

 

woo lol sounds like someone removed the cap and rewired the plugs wrong what you should do is take spark plug for cyl #1 out bring engine to top dead center on its compression stroke !!!! key !!! to tell if its on the compression stroke put your finger in the plug hole and feel for pressure! now once tdc take the distrib cap off see where the rotor is in line for take that plug wire and put it on that spot then rewire the cap with the corect fireing order and done no need to move the distrib cause can be a big pain to get back in when you turn the gear cause you have to alighn the pump too !!!! good luck

Tom

 

what side of the engine are you checking the timing on...?

on my 95 it is on the passenger side ...on the front cover marks it only lines up with #2 but it is off...

 

It seems that everyone has pretty much the same general ideas of what it could be. To answer some of the questions, yes when checking the timing I pulled that small jumper plug and hooked my light up to #1 and pointed the light at the balancer with the marks on it. (As instructed by the Haynes manual) Can't see the damn mark! Not to sure what you mean Dr Bowtie when you ask what side I check the timing from?

Now that you guys have pointed possible causes I am going to make further checks this week starting with the firing order!.

If the order is wrong would it still idle fine?

Appreciate all your help and I hope to get to the bottom of the issue. I owe this truck a lot of thanks as even though she runs rough at times she just can’t be broken!

 

Personally what I would do to save yourself much headache...just get your correct firing order get the balancer pointing at 0 and pull the distributor out an drop it in so it's pointing at #1. You might have to use a small socket with a long extension to turn your oil pump drive after the dist is out so it will drop in but you may not. Then take your timing from there. That rules out any question of the dist being in the wrong spot. By the way if it doesn't start after you do that pull the dist back out and aim the rotor in the opposite direction. That just means you were 180 degrees off.

 

Ok...

get under the truck and look at the balancer...there will be a notch and a mark..the mark is the one you want..it will be a thin line..very thin...I sand and paint the line and wipe off the balancer to make sure only paint is in the line....

then what I mean is on my truck there are 2 timing tabs...one is cast into the front cover that has marks on it with the numbers...this is cast into the timing chain cover and shows in top and bottom right next to the balancer...

there is also another timing tab on the left hand side of the engine just to the right of the AIR pump right at the balancer at the 9 o'clock position...this is the one I need to use....

this one just looks like a saw blade kinda looking thing with small stamped numbers...you can barely see them...

if you have both tabs then use the one that lines up with number 1...

I will say the left one (passenger side) was all grimy and I had to clean it to even see 0...but that one goes from 0-50 all in the same...

 

Is "0" top center of the balancer? As in O degrees'?

 

No...0 is TDC or Top Dead Center...this refers to the #1 piston being at Top Dead center...being at the highest it can be in the cylinder in the center of it's travel....