So I have a 1985 Jeep XJ with a 1986 Bronco EFI 302 in it.

It started running crappy at intersections and lurching and such. So after searching here using "idle" "problems" things like this I thought it might be the Air Idle Motor. This weekend I took the unit off and the rod valve section it acuates and cleaned them. I also cleaned my remote air filters as they were pretty dirty.

Put it back together and try to fire it....won't start :confused: Will crank awaaaayyyyy and no start.

So here is what I checked:

1. Fuel pump's are working...making noise and you get some fume'age after a while of cranking :)

2. I am getting no spark to the plugs. I jammed a screw driver into a plug end and held it to the manifold...nada.

3. Moved to coil...I have no voltage on the hot side of the coil with ignition on.

4. Double checked the coil to ensure it was within readings....it was...internal resistance was 3.something, and hot side check was 9.8...right in the middle of the specs.

So a neighbor who has a 5.0 Stang came over and helped me look farther into it...he mentioned that the "Thin Film Ingition" module is known to go bad for no reason...well that is what made me search...and that is what seems to be the general consensus...that those things fucking suck!

Things I learned while searching:

Shorts can take out a TFI......I have some crappy wiring splices in this circuit that could have been the cause.

Try to get the best "quality" TFI unit you can.

Might be good to carry a spare.

Use HEATSINK paste instead of the Dielectric Paste that will come with the unit.

Buy the little 5.5 MM thin wall Ford TFI removal tool......You know it must be a pain in the ass when they make a special tool to make removal easier!


So based upon my diagnosis...am I right in assuming the TFI is the culprit?

Mark

will it start if you feather the gas?

it would seem.. it half assed worked untill you clean the IAC.. then it didn't. If you manually open the throttle and it runs, it's probably still the IAC. Otherwise, yes, the TFI is a rather fragile pile of shit. But to get a decent replacement your gunna spend decent bucks on it. Better rule out the IAC first. (you can also just unbolt it and start it with it off, if it runs again, it's the IAC)

Which IAC do you have? If it's the all-plastic body one, it's not cleanable and chances are you killed it when you tried. Only the metal one is cleanable.

Thanks for the reply...

Remember it is not even getting spark to the coil for triggering the motor... :(

that is why I am assuming TFI.

As for my IAC it is a metal bodied motor...?

sounds like TFI to me IIRC autozone has the ability to test them to confirm your problem since it is there when it is cold.

So....

Wells...cheapest

Accel...cheap

Elchin (sp)...most $$

the current unit that is (might be) bad is a Wells and looks to be old...

Opinions? Buy two Wells and have a spare?

Didn't catch the no spark part

Well if it's dead, like was said, they can be tested while cold.. if it's dead it's dead. (unlike when they die after being warmed up)
Whatever you do buy, buy 2 either way. Buy a good one, and a cheap one for a spare, so it's there WHEN you need it.

I've had good luck with Borg-Warner branded TFI's in the past. (found mine at checkers, ~$70 IIRC)

without having priced them my guess is the Elchin is 2X the wells and the Accel is about 1/2 way between them. Personally I don't want to change one on the road if it goes bad b/c I'd leave the 5.5mm @ home :D but that's me & my luck. Personally I would by a good one then you don't have to worry for a few more years by then I'd have busted the spare one.

3. Moved to coil...I have no voltage on the hot side of the coil with ignition on.




i wouldnt buy two tfi modules.

i wouldnt buy two tfi modules.

why not? explain....

bobbywalter has brought up a good point. I'd overlooked it the hot side of the coil meaning you arent' getting power to the coil. the power to the coil would be controled by ignition

bobbywalter has brought up a good point. I'd overlooked it the hot side of the coil meaning you arent' getting power to the coil. the power to the coil would be controled by ignition

Well I am going to run with the TFI being bad. There is a green wire coming from the TFI Module plug that goes to my coil. It is the only wire on the positive side of the coil. I don't know enough to rebute anything else.. :confused: And according to a Mustang wiring diagram with the TFI...that is what passes the voltage through to the coil. If it does not collapse the field then the 12v won't pass to the coil. So I am assuming that it is bad and the field is open = no voltage.

How do they test those things?

All the circuits that are on the INGITION side of the key turn, come on. I have not had a problem yet with this thing....it was running very smooth...Then started running shitty...Now dead in driveway.

one side of the coil is always hot once the ignition is on. the other side is a switched via the TFI to GROUND. if you take a powered test light to find a ground, as you crank you should be able to see it flash as the circut it closed via the TFI. No pulsing, means the TFI isn't working.. (but don't forget, the TFI might not be working due to other reasons also..)

unless the TFI setup is backwards and the pos side is the controlled side, all the systems I've ever worked on the ground was the controlled.

I just called the local parts store that I trust...and they can test the TFI's. So I am going to buy the tool and take mine in tomorrow sometime. I have a feeling that the tool will be needed in the future from all the searching I have done here on Pirate :)

It will remain in the "trail box" to. Not in the tool cabinet... :)

actually you can cold test it with a dvom. if the hot side of the coil is dead then you may have a loose/disconnected wire elsewhere.


i assume you have a dist mount tfi and not a remote.



listen...if i were you i would run a hot wire to the coil before you take anything apart....crank it up...if it runs...find the fault to the coil. if it dont run then go test your module....i am short on time again today so i cant go thru the routines to dvom your tfi but will later if you pm me.

actually you can cold test it with a dvom. if the hot side of the coil is dead then you may have a loose/disconnected wire elsewhere.


i assume you have a dist mount tfi and not a remote.



listen...if i were you i would run a hot wire to the coil before you take anything apart....crank it up...if it runs...find the fault to the coil. if it dont run then go test your module....i am short on time again today so i cant go thru the routines to dvom your tfi but will later if you pm me.

Thank you...

I will give that a try this afternoon before I spend any $$. I understand now what you are all refering to.

I should always have a hot (12volts) coil and the TFI is what collapses the field on the NEG side. So if I run a new 12v wire directly to the coil and it runs....then the TFI is collapsing the field as it should...and I have a different issue...

Makes sense...

:smokin:

TFI tested "good"...they ran it 4 times.

So I guess that I am now going to have to put it all back together and start tracing the positive side of the coil.

There is nothing else in the Dizzy or that area that could be giving me no hot side voltage is there?

I really appreciate all the suggestions you guys have. I am going to be moving along to the Jeep forum now :(

FWIW I've had TFI's "test" good, but not still not work. Best bet would be to swap in a known good TFI.
I've had very mixed results with any aftermarket TFI module, so I've just started bending over and getting one from Ford direct...

I am going to revert my steps and follow all the ones who have mentioned that even though the TFI Module "tests" good to replace it anyway.

I have this afternoon checked fused links...Ignition switch...Battery connections, grounds, and still no fire.

My neighbor and I have a bet going as he agrees with all of you about the TFI. He thinks that I will go down tomorrow, buy one, throw it in and Varrrooommm....I am not so optimistic.

I bet him a dozen muffins...I bake them.

I will take a photo of the muffins and you all can say I told you so if you are right

:flipoff2:

Well yesterday I picked up a new TFI cleaned the surface plates applied lube...and installed the new unit. Did a triple check of all the wires that I had been fucking with and tried to fire it up...

STILL NO FIRE :mad3: No spark at the coil... :shaking:

Soooooo I debated burning the fucking thing and calling my insurance agent...while standing there I recalled how someone mentioned that they had a shorted TACH wire against the ignition wire and their XJ wouldn't run...

Upon further testing I removed all the non essential toys from the wiring and found that the tach power wire was on the same spade connector as the resistor wire for the ignition unit. The TACH in this thing was a piece of shit to begin with...

...Since the Tach took a shit it was basically changing the OHM's on the resistor wire...Not allowing enough or whatever to the ignition. I unplugged the Tach power wire and I instantly had 11'ish volts with keyed ignition... :)

Tach is going to get tossed as far I can huck that fucker....and then I just need to set the timing...

Thanks for everyones suggestions and thoughts...I have learned a hell of a lot about my 302 just from this thread and SEARCHING :cool2:

easy test, if the fuel pump runs when the key is in START, the TFI is good.

fuel soaked plugs, or fuel out the tail pipe is a good sign, but the pump running while starting = 100% good TFI test.