Missing, backfiring Mustang

BlakesStang · Oct 19, 2020

Hi all,
Got my son's mustang running after some effort.. a lot of effort.
He drove it for about half the summer and it suddenly started missing and backfiring. Hard starting and basically undrivable.
Tried a few things, tested maf and tps with a dvm.. seems ok. After messing around decided to take it to a shop. They were unable to get any codes.. stupid OBD1.
Anyway, they were not able to nail it down but told us best guess is the timing chain. So, we took it home and changed out the timing chain. Old was pretty slack so hopes were high. Got it back together.. no change. Still not running, backfire, missing.. pretty much the same deal.
I am out of ideas, this thing is killing us both.
Any help would be VERY appreciated!
Any ideas guys?

General karthief · Oct 19, 2020

Cranks OK, but No Start Checklist for Fuel Injected Mustangs

Cranks OK, but No Start Checklist for Fuel Injected 5.0 Mustangs model years 1986-1995 A word about this checklist before you start: it is arranged in a specific order to put the most likely failure items first. That will save you time, energy and money. Start at the top of the list and work...

www.stangnet.com

Start by reading through the checklist to make sure you understand and have the tools, pay attention to the highlighted notes that are for 94-5 stangs, take notes, ask questions here and the members will help you.

BlakesStang · Oct 19, 2020

General karthief said:
Cranks OK, but No Start Checklist for Fuel Injected Mustangs

Cranks OK, but No Start Checklist for Fuel Injected 5.0 Mustangs model years 1986-1995 A word about this checklist before you start: it is arranged in a specific order to put the most likely failure items first. That will save you time, energy and money. Start at the top of the list and work...

www.stangnet.com

Start by reading through the checklist to make sure you understand and have the tools, pay attention to the highlighted notes that are for 94-5 stangs, take notes, ask questions here and the members will help you.

That is quite a list but definitely worth a shot. I will give it a whirl as soon as possible.
Thanks!

General karthief · Oct 20, 2020

It saves you money and time, in some cases you have a couple things going wonky so do the complete list step by step, jrichker put it together with imput from others and I can tell you it works, I will say I had to do the list twice, but I had some self inflicted issues when I put my motor together.

BlakesStang · Oct 21, 2020

General karthief said:
It saves you money and time, in some cases you have a couple things going wonky so do the complete list step by step, jrichker put it together with imput from others and I can tell you it works, I will say I had to do the list twice, but I had some self inflicted issues when I put my motor together.

Understood, trying to get through the checklist. Made it past spark tests, fuel pressure good, noid light on injector flashes. Tried starting at 1/4 throttle and no go. So I am to the failed computer or ignition or cam timing off.
We did change the timing chain on advice of a mechanic but seems to be acting the same as it did. That said I suppose it is possible timing is off. We were very careful with the timing chain installation so hoping that is not it. Any advice on setting timing on a non running engine? I know the shop we took it to played around with it and now we are too.
By the way we did check compression and we are at about 120lb. Also.. and maybe I should have mentioned this at first, but we had a dead coil when all this started. Swapped out for a new one, engine ran but not well. Swapped it for another new coil and no ignition at all. Put the other new coil in and it at least pops. Maybe that is significant?
Thanks in advance!

General karthief · Oct 21, 2020

Pull the plugs, crank the engine over with your finger over the #1 spark plug hole, when you feel air coming out stop and stick a small screw driver into the plug hole and turn the engine by hand feeling the piston push up on the screw driver, when the piston stops coming up and before it moves down look at the pointer at the balancer and it should point to 0*, you may have to turn the engine (by hand) back and forth to get the piston at the top of the stroke, the rotor should be pointing at the #1 spark plug terminal. This is top dead center or 0*.

BlakesStang · Oct 22, 2020

BlakesStang said:
Understood, trying to get through the checklist. Made it past spark tests, fuel pressure good, noid light on injector flashes. Tried starting at 1/4 throttle and no go. So I am to the failed computer or ignition or cam timing off.
We did change the timing chain on advice of a mechanic but seems to be acting the same as it did. That said I suppose it is possible timing is off. We were very careful with the timing chain installation so hoping that is not it. Any advice on setting timing on a non running engine? I know the shop we took it to played around with it and now we are too.
By the way we did check compression and we are at about 120lb. Also.. and maybe I should have mentioned this at first, but we had a dead coil when all this started. Swapped out for a new one, engine ran but not well. Swapped it for another new coil and no ignition at all. Put the other new coil in and it at least pops. Maybe that is significant?
Thanks in advance!

General karthief said:
Pull the plugs, crank the engine over with your finger over the #1 spark plug hole, when you feel air coming out stop and stick a small screw driver into the plug hole and turn the engine by hand feeling the piston push up on the screw driver, when the piston stops coming up and before it moves down look at the pointer at the balancer and it should point to 0*, you may have to turn the engine (by hand) back and forth to get the piston at the top of the stroke, the rotor should be pointing at the #1 spark plug terminal. This is top dead center or 0*.

Ok, we got it timed pretty well I think. Turned it over and same thing. It just chugs a little but doesn't start. To me it sounds like not getting gas but we do have pressure (shop told me about 40lbs) and pressing the schrader valve we get a four or five inch geyser of fuel. Plus we tried some ether and still no joy. Went out and got a ford specific obd1 code reader which did return codes but it was low coolant temp and low transmission temp. Not much help there.
Not sure where to go from here. I guess I shouldn't expect it to be easy when it stumped the professionals but running out of ideas at this point.

General karthief · Oct 23, 2020

Go back to post #2, that should show you what is wrong if you do the steps one by one and in order, don't skip around.

BlakesStang · Oct 23, 2020

General karthief said:
Go back to post #2, that should show you what is wrong if you do the steps one by one and in order, don't skip around.

BlakesStang · Oct 23, 2020

Well, it does have spark which precludes a large part of the checklist. I will say however that the spark is not as blue as what is described. More orange and blue. Not sure how much difference that would make. That said we have replaced the coil, cap, rotor, wires and plugs. Still kind of orange.

General karthief · Oct 23, 2020

.) Coil weak or intermittent - you should see 3/8" fat blue spark with a good coil
Will it start or try to start using starting fluid?

BlakesStang · Oct 23, 2020

General karthief said:
.) Coil weak or intermittent - you should see 3/8" fat blue spark with a good coil
Will it start or try to start using starting fluid?

We have tried two different brand new coils and got the same type of spark. It is bright and a good 3/8 inch but not blue. More orange. And like I said, this disaster started with a bad coil, no spark at all.
No, it does not start with starting fluid. Strangely it seems we get less ignition with starting fluid. Thinking maybe it is getting flooded by the time we go to the starting fluid. Being we have replaced so much of that system.. not sure what would be left.
But then, I have no other ideas and am totally open to suggestions.

General karthief · Oct 23, 2020

Just curious, what type of spark plugs you using?
Is your coil connections good? I believe the coil is grounded through the bracket to the fender panel, does it look good, no burn marks?
Check spark at coil with screw driver to ground, then coil wire to cap
Check for proper voltage to the coil too. Does the tach react to cranking the car?

BlakesStang · Oct 28, 2020

General karthief said:
Just curious, what type of spark plugs you using?
Is your coil connections good? I believe the coil is grounded through the bracket to the fender panel, does it look good, no burn marks?
Check spark at coil with screw driver to ground, then coil wire to cap
Check for proper voltage to the coil too. Does the tach react to cranking the car?

Just checking in. It has gotten cold out but have not given up, just taking break. Probably get back to it this weekend.

rockyracoon · Oct 29, 2020

Seems stupid. But check that both wires in the connector that goes to the coil are all the way in the connector. I once had the same symptoms and that's what it was.

hftrud · Oct 29, 2020

BlakesStang said:
Hi all,
Got my son's mustang running after some effort.. a lot of effort.
He drove it for about half the summer and it suddenly started missing and backfiring. Hard starting and basically undrivable.
Tried a few things, tested maf and tps with a dvm.. seems ok. After messing around decided to take it to a shop. They were unable to get any codes.. stupid OBD1.
Anyway, they were not able to nail it down but told us best guess is the timing chain. So, we took it home and changed out the timing chain. Old was pretty slack so hopes were high. Got it back together.. no change. Still not running, backfire, missing.. pretty much the same deal.
I am out of ideas, this thing is killing us both.
Any help would be VERY appreciated!
Any ideas guys?

Mine had a similar issue. Finally removed the rotor and found a burn mark where is was shorting out on the buttom. Also check the cap for any signs of carbon from arching.

BlakesStang · Nov 1, 2020

General karthief said:
Just curious, what type of spark plugs you using?
Is your coil connections good? I believe the coil is grounded through the bracket to the fender panel, does it look good, no burn marks?
Check spark at coil with screw driver to ground, then coil wire to cap
Check for proper voltage to the coil too. Does the tach react to cranking the car?

Ok, a little warmer today so took a few minutes to check it out. Using autolite 25 plugs. Got 11.6v dc at the coil. Also got a pic of the spark. It seems a little weak to me.
Grounds seem OK.
Thoughts?

BlakesStang · Nov 1, 2020

hftrud said:
Mine had a similar issue. Finally removed the rotor and found a burn mark where is was shorting out on the buttom. Also check the cap for any signs of carbon from arching.

Yep, the old cap and rotor were not great but replaced them both. No change.

hftrud · Nov 2, 2020

rockyracoon said:
Seems stupid. But check that both wires in the connector that goes to the coil are all the way in the connector. I once had the same symptoms and that's what it was.

A really OLD school test for spark. remove the dist cap with all wires attached, turn it upside down and place a penny (clad quarter will do) half way between the center post and any two plug wire posts. Crank the engine and watch the spark. Should be a sharp blue line. Move the coin to the next two plug wire posts and repeat. If one or two are not firing correctly you have isolated the problem. If all is good you have eliminated everything from the plugs to the cap and the coil.

BlakesStang · Nov 2, 2020

hftrud said:
A really OLD school test for spark. remove the dist cap with all wires attached, turn it upside down and place a penny (clad quarter will do) half way between the center post and any two plug wire posts. Crank the engine and watch the spark. Should be a sharp blue line. Move the coin to the next two plug wire posts and repeat. If one or two are not firing correctly you have isolated the problem. If all is good you have eliminated everything from the plugs to the cap and the coil.

Well I'm pretty sure it's getting gas. It back fired loud enough to make my ears ring.
Think I will hang it up for tonight.

Missing, backfiring Mustang

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