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Randall008

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I have a 1987 Bronco II. I am not a mechanic. I replaced the TFI Module.

I Screwed something up.

I was getting some slight hesitation when I pressed the gas, the idle was a little rough, and a little rough on start up and going from drive to park. I figured the ignition system.

I checked the tfi module and the case was broken and the metal plate on the back was no longer attached so I figured that was the culprit.

I replaced it and it ran ok for about a mile, then it started sputtering and trying to die, lack of power. Now it starts up and dies with black smoke.

Ive swapped between a couple tfi modules to test if I had a bad module, no good.

I think ive either screwed up the distrubutor somehow, or the timeing was super off to make up for the fact that the old tfi module was broken, or I messed up the timing while I was back there fiddling with it.

My neighbor put a timeing light on it, and the bank on the drivers side is fine, but the bank on the passenger side has tons of missfires and bad spark.

Have I screwed up the distributor, did I accidentally yank the sprk plug wires or another wire that I havn't thought of. Is the timing just super off?

I will say it looks like the TFI Module sits closer to the valve cover gasket then it should. It's almot touching.

Any advice would be appreciated,

Thank You for your time
 


RonD

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Randall008

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Hi Ron,
Thank you for your response.
I am pretty sure the firing order is correct because it worked fine before I changed the module and I didn't unglug them. However, It is definitely possible that they are no longer tight. I easily could have pulled them loose while working on it. I'll check when I get home,
Thank you for the advise
 

RonD

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Everyone who has ever worked on a multi-cylinder engine "thinks" the firing order is correct

If a mechanic says they have never goofed up a firing order then you will know one thing FOR SURE about them, they are a LIAR, lol

I have no doubt your firing order is correct, until its not :)
 

Randall008

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Hi Ron,

That is a very helpful diagram to keep in my back pocket. Thank you.

To the best of my knowledge, the firing oder is correct.

I did notice that the plug wires on the passenger side felt a little loose so I put the old wires back on and it runs better, not perfect but better.

My plan is to replace the wires, possibly the plugs, cap and button for good measure.

If this works I will be quite happy, and frustrated because they are only 2 or three years old.

Thank you for pointing me in the right direction.

I will update in a few days if this resolves my problem.

Thanks again

Randall
 

Randall008

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Hi RonD,
Update:
I checked the plugs and they were fouled black.
I checked the cap and button and they both had a fair amount of corrosion.
Which again is weird because they are only 2 years old. I replaced all of them, and I took it for a test drive last night and it ran great except it had one miss, which I figured was a fluke. It ran fine after the miss. Better then it’s ever run.
I got in it this morning and nothing but misses.
could I have a bad pick up in the distributor?
thank you for your time
Randall
 

RonD

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If old spark plugs were "fouled black" then that's usually not a spark issue

1986-1992 2.9l engines used a Fuel Return system
On the engine is the Fuel Pressure Regulator(FPR), looks like a small can
The return fuel line is attached to it, AND a vacuum hose
If FPR leaks the vacuum hose will suck in extra fuel and cause RICH running
i.e. black spark plug tips and misfires from Rich Mix
Check that vacuum hose for gasoline

As said old O2 sensor will also cause rich mix, change it if you don't know its age


PCV valve, this needs to be cleaned or replaced every 3 to 4 oil changes
2 or 3 if engine is older, or if its obviously getting oil clogged

All piston engines have "blow-by"
When a cylinder fires some of the very HOT high pressure gases will "blow-by" the piston's rings and into the crank case
The rings and cylinder walls are lubricated with oil
The HOT gases will Vaporize some of that oil, this is THE ONLY PLACE in the engine hot enough to vaporize oil
Blow-by is exhaust gases

PCV system was added to suck up the blow-by gases and re-burn them in the engine, much the same as EGR system does but for another reason
But PCV system can also suck in the oil vapor
Newer engine will have 5-8% blow-by
As the rings get worn 9-12% blow-by
When it gets up past 15% the oil vapor can clog PCV and start to foul spark plugs

Valve guide seals
The valve train needs oil but the intake valve stems can suck this oil in because of the high vacuum in the intake, so there are valve seals on the intake and exhaust valve stems, inside the springs
Exhaust valve seals are not a big issue as far as engine operation
The intake seals ARE a big issue, as liquid oil can run down the stem and be sucked into the cylinders, this can cause misfires and black spark plug tips

A perfectly working Spark system can not over come any of the above
 

Randall008

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Hi Ron,
Thank you for the detailed response.
The bronco has always run a little rich. I get the faint hint of gasoline every now and then.
The fuel pressure regulator is relatively new but I will check the vacuum line when I get home. The O2 sensor is also new. A couple months old. The pvc is new within a couple thousand miles but I will check that as well. It’s always run a little rich, but performed. It stopped running when I swapped out the tfi module. So I’m wondering if I pulled a vacuume line or something in that area that would cause the drastic change in it running so rich. When I swapped out the module it ran fine for a couple miles and when I swapped out the plugs and wires it ran fine for a couple miles before starting to miss. I think whatever I did is causing it to run super rich, and after a couple miles it fouls the plugs and starts running rough. Is there anything in the area of the tfi module that I could have pulled to create this.
Again thank you for your time,
I appreciate the guidance
 

Randall008

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Update:

I replaced the pcv valve.

I swapped in an fpr that I know works.

I replaced the map sensor because it was full of dirt

I haven’t touched the O2 sensor, but it’s only a couple months old.

It runs worse when it’s warm. Should i unplug it as a test to see if it runs better

did I brake a fuel injector wire?

the valve guide seals exhaust seal, and the intakes seals are beyond my mechanical abilities, but I wouldn’t think they would fail all at once the moment I replaced the tfi module.

Any more advice? I’m at a loss

thank you
 

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Have you timed the spark for the engine yet?

Check a couple of spark plug tips, see what they tell you about rich or lean running

Cold engine runs off air/fuel mix tables in computer memory
Once engine is warm the computer calculates air/fuel mix on the fly
 

Randall008

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Thank you for your response.

I don’t have a timing light, and my neighbors broke. I checked that I had spark with one of those inline spark plug wire bulbs. Could changing the tfi module alter the timing or should it?

I checked the plugs, they are black again
That’s maybe 10 miles

thank you
 

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gaz

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@Randall008 ,
@RonD beat me to it, verify the timing correct. I believe you can rent any diagnostic tool from The AUTOZONE, WESTBAY-NAPA, Schuck's/Kragen/Checker's/O'Reilly's.
 

Randall008

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Good morning,

This is my last day off for a while so if I don’t get it fixed today, it will probably sit for a while.

I’m going to try and check the time if today, but I am a novice at this. Any pointers would be appreciated.

I’ve looked at a lot of you tube videos and I think I have the general idea. According to my emissions panel I want the timing set 10 degrees before top dead center. There is an arrow over the harmonic balancer that I assume needs to line up with the 10 degree mark on the harmonic balancer while the truck is idling and the spout connected is disconnected.

what is the circular piece of metal over the harmonic balancer?

to correct timing I loosen a bolt on the distributor and move it slowly is that correct?

thank you
 

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Randall008

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Update:
The timing was off. I rotated the distributor about a quarter of an inch, checked it again and the markers lining up.
It still didn’t run right so I took the plugs out, and put a blow torch on them.
I’ve run it about 15 miles now and it’s running well.
Thanks for all the suggestions
Randall
 

Randall008

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Update number 2

I’ve driven it about 30 miles.

it runs and idles now which is more than can be said for this morning.

it’s lost power twice, but other than that so far it feels pretty good.

I pulled a plug. It looks like it blackened up a little from when I hit it with the torch.

the exhaust is not smoking anymore, but the pipe is still black, and sometimes it’s got Water droplets in it.

should I just drive it and see what happens? Fiddle with the timing some more? Replace the plugs again?

thank you
 

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