Hesitation/excessive Backfiring At High Rpms.

92BlackWidowHO

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Jul 24, 2011
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Today I was taking my brother for a ride and when I stomped the throttle, it performed greatly, and I as I went into 2nd, it started backfiring and hesitating severely around 4500+rpms. As long as you drive it below the 4500 range, it drives just fine all day. It never did this before as long as I've driven it. No engine noises. I cranked it this evening and I heard a extremely loud clicking noise under the hood, and it was coming from the tfi coil. It made a noise in the past but its now extremely noisy! Its a msd blaster coil. The timing has been checked and adjusted to different degrees and it has no change in performance. Plugs are new and so are the wires. Any suggestions as what it could be? Like I said, as long as I drive it below 4000 rpms, I can drive it all day with no problems. Check engine light is not on. Thanks.
 
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jrichker

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The TFI module mounted on the distributor is usually the culprit for a high speed miss on a warm engine. If the problem does not occur when the engine is cold, the TFI module is definitely suspect. You may need a special socket to remove the TFI module, but most auto parts stores will have one for $5-$7.

Be sure to use plenty of the heat sink grease on the new TFI and clean the old grease off the distributor.

View attachment 147708

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92BlackWidowHO

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I swapped out a spare distributor and it still does the same thing. I tried doing a computer test and its saying "O2 Sensors triggered engine running lean. I tried giving half throttle all the way to 6000rpms, no backfire, 3/4 throttle, no backfire or hesitation, but when I give it wot, all hell breaks loose and sounds like a gun going off and I lose 50% of power. As long as I don't WOT it at 4000+, it runs great! I cleaned the O2 sensors thinking maybe it being dirty could be a problem. MAF sensor is clean too. When I first crank it, it wants to stall immediately unless I keep the rpms near or around 1000rpms for like 10 secs, then it idles really rough like it wants to stall. But driving it cold I have no problems whatsoever. It will perform wonderfully all the way up to the red line mark. Once it warms up, it idles fine with no problems, then the backfiring/hesitation occurs. I did throw a code right around the time it started backfiring/hesitating. Saying engine running lean. Stock MAF, CAI, Stock engine with a mild cam"don't know what kind it is." It drove fine for 3 weeks after driving it for the first time with no problems at running temps. I thought timing may have been the issue, but wherever I adjust the timing, advanced or retard, it does the same thing. Engine only has 69K original miles on it. I run 93 octane in it.
 

jrichker

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What were the exact codes you got? You have a lean condition at WOT, which could be anything from a sensor or fuel delivery problem to a vacuum leak.

If you have a air filter that uses an oil coating (K&N), clean the MAF element with some spray electrical contact cleaner.
 

jesseover

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The TFI module mounted on the distributor is usually the culprit for a high speed miss on a warm engine. If the problem does not occur when the engine is cold, the TFI module is definitely suspect. You may need a special socket to remove the TFI module, but most auto parts stores will have one for $5-$7.

Be sure to use plenty of the heat sink grease on the new TFI and clean the old grease off the distributor.

View attachment 145163

See Automotive Tools Specialty | Auto Mechanic & Technician Diagnostic, Testing Equipment | Thexton
I went to three auto stores today asking for the TFI module but no one seemed to know what that was, nor were they able to find it on the data base. Is there another name for that part? Thanks!
 

MFE92

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Check your grounds and make sure your #7 ignition wire isn't touching the dipstick and that #5 and #6 don't touch each other.
 

jesseover

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Check your grounds and make sure your #7 ignition wire isn't touching the dipstick and that #5 and #6 don't touch each other.
I am having that warm engine about 4000rpm problem, like some other people. When the motor is cool, or the first 5-7 minutes the motor pulls all the way throught the rpms, then I get the hesitation after the motor is warmed. Seems like TFI is culprit...what ever that is:shrug:
 

dcurtis

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Is this the part I am looking for? http://thexton.com/index.cfm?pageid=42&search=tfi
The Ford E-Core coil adaptor. AKA TFI module.
No, just go to any parts store and tell them you need an ignition module, 90% of them will say they don't know what a tfi module is, its the small grey piece mounted on the side of the distributor. cost around 30 bucks. Doesn't really sound like a tfi problem to me though.
 

jesseover

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Intially I suspected the valves, then I read that the 5.0 motor does not need the valves adjusted. I am a Datusn guy recently switched over to the fox body. I am seeing the tolerences with the valves increasing as the motor warms. Am I off here?
 

jrichker

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Intially I suspected the valves, then I read that the 5.0 motor does not need the valves adjusted. I am a Datusn guy recently switched over to the fox body. I am seeing the tolerences with the valves increasing as the motor warms. Am I off here?
All the stock 5.0 engines came with hydraulic lifters. When valvetrain is in good shape, the lifter clearances are not a problem. From 86 on, all the HO engines came with hydraulic roller lifters.
 

pissedoff92

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Having the wires touch can acctually cause a miss? Anyways if you ask for the module tool your gonna get wierd looks. I just bought one at advance and I know autozone sells them as well. Either way its gonna be a double sided deal with a small 5.5mm side and the other is a small torx bit
 

jrichker

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Having the wires touch can acctually cause a miss? Anyways if you ask for the module tool your gonna get wierd looks. I just bought one at advance and I know autozone sells them as well. Either way its gonna be a double sided deal with a small 5.5mm side and the other is a small torx bit
Spark plug wires that run parallel touching or in parallel in close proximity to each other can induce enough voltage in each other to cause a misfire. This is due to the magnetic field that surrounds each wire when it is carrying current. Then the spark plug fires, the magnetic field collapses and causes an electric pulse in the closely adjacent wire.
 

MFE92

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Having the wires touch can acctually cause a miss? Anyways if you ask for the module tool your gonna get wierd looks. I just bought one at advance and I know autozone sells them as well. Either way its gonna be a double sided deal with a small 5.5mm side and the other is a small torx bit
Yes, the electrical pulse will follow the path of least resistance. In the case of #5 and #6, they're next to each other in the firing order, and if the wires are touching, the pulse intended for 6 sometimes finds less resistance jumping to 5 than it does going through the compressed charge waiting in 6. Same thing with the plug wire that likes to rest against the dipstick tube, sometimes it's an easier path to ground to arc to the tube than it is through the plug.
 

jesseover

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Just a note here. I initially replied to this thread because of the hesitation in the title, I do not get backfiring. I will check the plug wires tomorrow and get an ignition module---plugs first. Besides this minor annoyance, I am loving my '91. The odometer says 140,xxx but the cars runs storng and smooth, and sounds badazz. I get as many looks and comments on this ride then I did with my Datsuns. The 2.73's are a little slow, but it's real fun pulling from 35mph on up. Fox body's are the :poo:e.
 

pissedoff92

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Aug 14, 2011
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Try it with 4.11's lol. The reason I was curious about the wires touching is that I dont have wire looms on mine and I have a problem with cylinder 8. I cant pinpoint the problem either. MFE92 maybe you could assist on this, I have a thread already. I believe its titled breaking up above 2k. take a look and offer any kind of guess you can give. The problem is very similer to this OP's but my backfiring and missing starts at 2 grand. Idles great
 
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