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Author Topic: 1993 Cobra... Popping/misfiring intermittently  (Read 28556 times)
kilby91
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« on: July 06, 2015, 02:54:28 pm »

I have a 1993 Cobra with 42,000 miles. I got the car from the original owner in Indiana. The car is nowhere near stock and has had a lot of work done to it over the years. It was a twin turbo'd 347 for a long time, but when I bought it was back to the naturally aspirated 347 setup. Its a really nice car, but it was a weekend driver/track car for the previous owner so it hasn't been babied...

When I got the car in a trade I got it knowing that it had a couple issues I needed to work out. When I got it home last year it would barely crank and when it did, it ran like crap.. I checked the codes and the car was missing the ECT sensor, had a couple grounds that were loose, bad MAF, etc... I fixed all the codes that is was showing and got a new Pro M meter and injectors. By this time the car was running great except for the high rpm miss under load.. So I quit chasing this problem and concentrated on other things with the car.

Its been over a year now, and I have been working on the car almost non stop with different projects over the months. Now it runs great in every aspect except for cruising at a constant speed in high gear I can still feel a random miss every now and then and it sometimes stutters under WOT pretty bad. It seems like the problem shows up/gets worse when the car warms up.. I have read a lot and tested most things that I know how to do so far. Here is a list of what I have done so far:

Timing set to 16*
Fuel pressure is set to 42# and holds constant under load.
Spark plugs are new and are gapped to 0.040"
Spark plug wires are new Ford racing and are not arcing to anything that I can see.
Cap and rotor are in good shape.
TFI has been replaced
Valves are set to 1/4 turn past zero lash
Tested for vacuum leaks and none are present.
EGR has been deleted completely with EGR delete plug.
Pro M MAF meter cal'd to 42# injectors (Car has A9P processor)
The car has an externally mounted 255 LPH fuel pump with braided fuel hose all the way to the fuel rail.


The car is not showing a CEL, and the only codes it is giving have to do with emissions stuff that I have deleted. It runs and drives great right now, except for a light miss cruising at low rpm, and the stutter under WOT.. Sometimes it screams like it should, and sometimes it stutters so bad that it doesn't accelerate very well at all...

HELP!!!! I don't know what else to check!!! Car idles great, drives great, everything is good except the intermittent miss that appears while cruising/hard accelerating when the car warms up..

Thanks,
Richard



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Joel5.0
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« Reply #1 on: July 06, 2015, 07:52:35 pm »

Remove the A9L ECM. Open it up and check to see if you have the classic e-caps leaking and other PWB lines issues .... http://sbftech.com/index.php/topic,37302.0.html. LUK
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'86 Mustang GT, X-303 cam, Holley DP 700, RG Tran., 289 Heads   Ford Smilie 2


Quote from: Joel5.0
The right to be stupid is inalienable for sure however, there is no such thing as a right to impose stupidity onto others
Great Thoughts will Overwhelm a Feeble Mind
There is never money to do it right, but there's always money to do it over.
Knowledge based on external evidence is unreliable.
He, who doesn't ask, does not deserve an answer.
A mind is like a parachute it only works when it is open.  (oldmanjoe)
If you can't explain it simply, you don't understand it well enough. (Albert Einstein)
Tuning on a Dyno for the track, is like swim practice in a bathtub.
I can explain it for you, but I can't understand it for you. (90lxcoupe)
The proof of understanding is the ability to explain it. (H. Torruella)
Ignorance is bliss, but stupidity is orgasmic.
Fraud and falsehood only dread examination. Truth invites it. (Samuel Johnson)
The chaotic resistance of the opponents leads to the conclusion that they are not prepared to meet the challenge. The problem is already much more psychological then technological. [Bojidar Djordjev]
Individuals are rational and humane... Crowds are reactionary and barbaric. (Jason)
The person who says it cannot be done should not interrupt the person doing it. –Chinese Proverb
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kilby91
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« Reply #2 on: July 07, 2015, 10:30:06 am »

I will pull it today after work and report back.

Thanks,
Richard
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kilby91
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« Reply #3 on: July 10, 2015, 02:00:28 pm »

Sorry for the delay, but I did pull the computer and take a look at it. Everything looks good to me. I inspected all the e-caps and looked over all the circuits, and everything looked brand new to me.


I also tried a different distributor, TFI, re-adjusted valves, etc..

Fuel pressure is @ 42# vacuum unplugged.

Between 13-14" of vacuum at idle.

Still not showing any codes, but the cylinder balance test keeps giving me different results.

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Tommy Hillbilly
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« Reply #4 on: July 11, 2015, 06:11:58 am »

Where did the replacement TFI module come from?  If it's from the McParts store, it might be the problem.
Did you replace it yourself, or was it on there when you got the car?
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1988 Mustang GT convertible, T5, 3.08:1 gears, A9L Mass Air conversion, Fenderwell Mac cold air intake, Ford 70mm MAF meter = 4.6 T-Bird housing + '94 Mustang F2VF-12B579-A1A sensor, aftermarket 70mm throttle body and spacer, Explorer intakes, GT40P heads drilled to rear ports for thermactor with Alex's Parts springs and Crane F3ZE-6529-AB 1.7 roller rockers, Ford Racing P50 headers, Mac H-pipe, Magnaflow catback, Walbro 190 LPH fuel pump, UPR firewall adjuster and quadrant with Ford OEM cable, 3G conversion ('95 Mustang V6), Taurus fan, rolled on Rustoleum gloss white paint.  KOEO: 11, CM: 11, KOER: 11, CB: 9.
kilby91
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« Reply #5 on: July 13, 2015, 10:26:34 am »

Well the Ford TFI is still on the stock distributor, I have tried different distributor/TFI combo and the same problem still exists... But I did swap coil wires and the problem seems to be better/fixed... I drove it 100 miles Friday night and it ran pretty good, still has a slight miss at cruising speeds, but the stumble under WOT is gone!!?!? I think.....

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stp-a-syd
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« Reply #6 on: July 14, 2015, 12:59:04 am »

this sounds like the same problem i once had. My problem was due to the spark plug wires being routed nice and neatly. The spark was jumping across wires due to the firing order and the proximity of plug wires to each other. The fix was to replace the wires and plugs,,,,,,,,(the problem ruined a brand new set) and to re-route the wires all crappy looking (away from each other). Maybe Joel remembers the Ford service bulletin??? Its an easy fix and cant hurt to try.
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kilby91
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« Reply #7 on: July 14, 2015, 09:26:24 am »

Well I am hoping that this was the issue and it is resolved, but I guess time will tell.. This car had the black Ford racing wires that look brand new, so I never even thought twice about them being the culprit. Then I noticed that the coil wire was a different brand/size wire than the rest of them. Replaced it with an MSD 8.5mm wire I had laying around, and it seems to have fixed it. I ordered a new set of black MSD super conductor wires that will be here in a day or so. I'll report back with the verdict if this solved it or not.

But the car still has another issue that I cant figure out, I had forgot to mention it until now. When the car sits overnight or for an extended period of time, and you crank it up... It ALWAYS goes dead within the first2 seconds of cranking it.. The second time you fire it up it'll run great, but it always dies the first time.. I have no idea what that means and its kinda annoying, but its not a huge problem... But if it is related to my ongoing issue I would like to figure it out as well.


Thanks guys
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kilby91
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« Reply #8 on: August 06, 2015, 09:47:12 am »

Well, new plug wires didn't fix my issue. Its still there just like it always has been.

One thing I have noticed lately is that I have to cycle the key on and off 4 or 5 times before the fuel pump primes up??? Not sure what that is all about. I have a fuel pressure gauge on the cowl, and it takes quite a while for it to build pressure. But once it primes then it cranks and runs normally.. But "normally" with this car means, intermittent sputtering under load... Not sure what else to change out/test at this point.

Thanks
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Joel5.0
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« Reply #9 on: August 06, 2015, 10:32:57 am »

Rerun the KOEO and KOER self tests with engine at op temp and LUK what codes are displayed.
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ACRONYMS:
LUK  LMK  JIC  BTSTDTRT  YCYDYP  NFI-YTM  SPOBI, and the classic... DILLIGAS

'86 Mustang GT, X-303 cam, Holley DP 700, RG Tran., 289 Heads   Ford Smilie 2


Quote from: Joel5.0
The right to be stupid is inalienable for sure however, there is no such thing as a right to impose stupidity onto others
Great Thoughts will Overwhelm a Feeble Mind
There is never money to do it right, but there's always money to do it over.
Knowledge based on external evidence is unreliable.
He, who doesn't ask, does not deserve an answer.
A mind is like a parachute it only works when it is open.  (oldmanjoe)
If you can't explain it simply, you don't understand it well enough. (Albert Einstein)
Tuning on a Dyno for the track, is like swim practice in a bathtub.
I can explain it for you, but I can't understand it for you. (90lxcoupe)
The proof of understanding is the ability to explain it. (H. Torruella)
Ignorance is bliss, but stupidity is orgasmic.
Fraud and falsehood only dread examination. Truth invites it. (Samuel Johnson)
The chaotic resistance of the opponents leads to the conclusion that they are not prepared to meet the challenge. The problem is already much more psychological then technological. [Bojidar Djordjev]
Individuals are rational and humane... Crowds are reactionary and barbaric. (Jason)
The person who says it cannot be done should not interrupt the person doing it. –Chinese Proverb
Nothing sways the stupid more than arguments they can't understand - Cardinal de Retz
kilby91
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Location: Jackson, MS

« Reply #10 on: August 06, 2015, 10:40:19 am »

I did run codes again this past weekend. The only codes that it threw were for the secondary air injection and charcoal canister.. I recently installed the EGR bypass plug so it doesn't throw that code anymore. I still haven't passed a cylinder balance test with this car, but every time I run it it gives a different cylinder number. Sometimes 2 cylinders.

I will run them again when I get time though and report back. 

Thanks,
Richard
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RunninHorse
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« Reply #11 on: August 07, 2015, 09:13:06 pm »

FWIW my high RPM miss was fixed by a new distributor.  Even though I previously put all new electronics on my factory distributor and cleaned it up.  If both distributors you tried were OEM I wouldn't rule that out as the cause yet.


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I'm Rob.  Working on my '93 Reef Blue coupe.  Stock internal 302, 80 MAF, 75 TB, Victor 5.0, High Ports, 30# inj., B303, 1.6s, Tremec TKO 3550, Quicktime bell, Fidanza Al flywheel, stage 3 ceramic clutch, & 4.10s.  12.68 @ 111.69
'66 F100 shortbed, 352ci, 3 on the tree - on hold
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kilby91
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« Reply #12 on: August 10, 2015, 10:49:19 am »

I still have the OEM dizzy, but I also bought a parts store Richporter Tech. dizzy and there is no difference in performance. Has the same miss/studder with both distributors. I am starting to think it could be related to fuel delivery.. It never loses pressure on my gauge though. I am stumped..
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Joel5.0
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« Reply #13 on: August 10, 2015, 11:12:04 am »

Suggestion, do a cranking compression test and LUK the results..
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ACRONYMS:
LUK  LMK  JIC  BTSTDTRT  YCYDYP  NFI-YTM  SPOBI, and the classic... DILLIGAS

'86 Mustang GT, X-303 cam, Holley DP 700, RG Tran., 289 Heads   Ford Smilie 2


Quote from: Joel5.0
The right to be stupid is inalienable for sure however, there is no such thing as a right to impose stupidity onto others
Great Thoughts will Overwhelm a Feeble Mind
There is never money to do it right, but there's always money to do it over.
Knowledge based on external evidence is unreliable.
He, who doesn't ask, does not deserve an answer.
A mind is like a parachute it only works when it is open.  (oldmanjoe)
If you can't explain it simply, you don't understand it well enough. (Albert Einstein)
Tuning on a Dyno for the track, is like swim practice in a bathtub.
I can explain it for you, but I can't understand it for you. (90lxcoupe)
The proof of understanding is the ability to explain it. (H. Torruella)
Ignorance is bliss, but stupidity is orgasmic.
Fraud and falsehood only dread examination. Truth invites it. (Samuel Johnson)
The chaotic resistance of the opponents leads to the conclusion that they are not prepared to meet the challenge. The problem is already much more psychological then technological. [Bojidar Djordjev]
Individuals are rational and humane... Crowds are reactionary and barbaric. (Jason)
The person who says it cannot be done should not interrupt the person doing it. –Chinese Proverb
Nothing sways the stupid more than arguments they can't understand - Cardinal de Retz
kilby91
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Location: Jackson, MS

« Reply #14 on: August 11, 2015, 09:00:28 am »

Here are the results of the latest self diagnostic check:

KOEO
81
82
85
84

KOER
94
44
33

Cyl. balance test #1
7

Cyl. balance test #2
8
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