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Discussion Starter #1
I'm still chasing this gremlin; it seems to have gradually worsened over the last month.

The symptoms are:

1) What feels/sounds like an ignition miss when the engine is under load. An example is when coming out of a turn and I apply moderate throttle (but not enough to force a downshift, so the engine is lightly lugging). I notice this only when things are good and warmed up.

2) Hesitation when accelerating from a dead stop. When the engine is cold, this is so severe that the engine nearly falls on it's face if I forget engage the throttle ever so gently; improvement is noted as the engine warms up, but is always evident to some degree.

Idle is good, no diagnostic trouble codes.

I don't know if these 2 symptoms are related; they may or may not be. It has had the hesitation problem much longer than the perceived miss problem.

What I've done:

Replaced plugs, wires, cap, rotor, checked timing (it was time anyway). I also substituted a known good coil; the symptoms remain. The only part of the ignition system I haven't messed with is the ignition control module.

My question is this: can a faulty igniton module cause such symptoms... can it fail gradually, or would it fail completely (like turning off a switch)? I was always of the understanding that they either worked or they did not... that there is no in-between.

Regards... Mike
 

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Very rarely will the TFI fail partially. I have had one do it - it would only start to fail after it got good and hot. They do generate quite a bit of heat, and do not have a large enough heat sink.

However, have you looked at fuel delivery? You say this only shows up under a load? Generally this is a sign of fuel starvation. You may want to check pressure and volume to help determine if this is a fuel issue.

When was the last time the fuel filter was replaced? Quick, cheap, and easy to do. Otherwise, you have the possibility of a FPR or the fuel pump being on it's way out.

The only way to determine this is by testing for it (pressure & volume).

I would bet your spark is fine based on what you have done already, and like mentioned, the TFI generally is a 100% fail item.

:x:
 

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In roughly 25 years of dealing with EEC IV / TFI Fords, I have seen a number of TFI modules "partly" fail, generating a miss when cold, a miss when hot, random stalling, etc. I have also seen intermittant PIPs several times. Often, but not always, either an intermittant PIP or intermittant TFI will set a CM code. FYI, Ford recommends replacing both the PIP and TFI if one or the other fails. Also, use ONLY Motorcraft parts when replacing these, and be sure to use thermal conductive grease on the TFI.
 

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Discussion Starter #5
zeptoplix...

I suspected that the TPS could be at fault regarding the hesitation condition. However, a resistance test indicates smooth operation throughout it's range; no dead spots are evident. I may try to borrow one to see if any change is noted.

Garry...

It's been about 25K since I replaced the fuel filter... I'll do that as well as check the pressure & volume before returning to the ignition system.

Jeff K...

Please forgive my ignorance... I figured out that a TFI is the ignition module (located under the cowl debris screen on this vehicle, evidently).

The PIP is giving me trouble though... I can't find it in my (official Ford) manual. Would you by any chance be referring to the Hall Effect device located within the distributor?

I appreciate the three of you taking the time to arm me with some fresh ammo. I'll follow up to inform you of what I find out (or return for more advice if I get stuck again!).

Regards... Mike
 

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Discussion Starter #6
Hi,

I replaced the fuel filter and checked the fuel pressure; it is good.

I temporarily disabled the EGR valve; no difference noted.

I borrowed a known good ignition control module; again, no difference noted.

I don't think it's a lack of fuel delivery, as FT acceleration is good. It's when under moderate load/light lugging situations that this problem appears. Of the two, I would think that FT acceleration would be the more demanding of good fuel delivery.

So, now I'm snooping around in the distributor.

According to my Ford manual, the leading edge of the vane should be centered in the vane switch stator ass'y when the #1 piston is at exactly TCD of it's compression stroke (0 deg). That is not what I'm seeing. I see the vane having moved beyond that (this distributor turns in a counterclockwise direction). My manual does not illustrate this relationship, so I'm unsure if what I have is correct. I've included a link to a photo for you to have a look at. What do you think... could that be enough to cause trouble? Perhaps the distributor drive gear/cam gear relationship is off a cog?

I do note, however, that when I set the #1 piston at 10 deg BTDC, which is the recommended setting, the leading edge of the vane is pretty close to being centered in the stator ass'y.

http://img5.ranchoweb.com/images/2crazy4stuff/dist.jpg

Regards... Mike
 

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I'll assume that the timing is set on that car in the old-school way, by rotating the distributor housing, in which case what you're seeing is correct. What I would take a closer look at is the shaft itself, specifically if the assembly has side-to-side shaft play. Your description of missing off tip-in just off idle, and at low RPM/high load conditions reminds me of Ford distributors I've had where the distibutor bearings wore which causes a shaft wobble. Then your pickup gap is goofy, with weak spark resulting.
 

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Discussion Starter #8
WJC,

Yes, the timing on this engine is set by rotating the distributor.

I checked for play: I found none side to side, nor did I find any up and down. There is 1/16" of axial play, measured at the vane, which I would think to be normal gear mesh clearance.

I may try substituting another distributor on the off chance that the hall effect unit is weak; however, I'm not expecting to learn of any revelations there either.

Regards... Mike
 

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HELLO,
I have had many issues with ignition modules over the yrs. Both GMC and FORD. I am current owner of a 1993 Taurus that I cannot find a good module replacement for, everyone I get jus dies out when the vehicle gets to operation temp. FORD has discontinued their brand and am dealing with after market.
 
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