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Random missfire

 
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William Jones
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Joined: 30 Jan 2006
Posts: 823
Location: Lake city, FL
28541.86 points


1971 Ford Mustang

PostPosted: Wed Feb 15, 2012 11:45 am    Post subject: Random missfire Reply with quote

I have a LT1 I built for a customer a few weeks ago he is 3 hrs away so trying to help him diagnose the problem. It runs fine then every once in awhile when he tries to accelerate it sputters then the check engine light flashes and stays on, the code says random mutiply missfire. This is in a 96 Impala SS the opti spark, plugs, wires, o2 sensors are all new. The crank trigger and coil are old but I would think it would always do it if they were bad. He can drive it like 20 to 30 mins and it will be fine then he resets the computer and it does it again. Kinda has me stumped without actually seeing the car.

Bam

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Take the horse out off the barn and let her RUN BABY RUN!!!!!

92 LX 454ci Clevor 9.24@142.53 N/A
71 Mach1 454ci Clevor 10.16@134 N/A 3850lbs race weight "Lost in fire"
03 Cobra Bone stock 12.42
68 Falcon 363ci 10.55@126 N/A
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Paul P
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Joined: 15 Aug 2002
Posts: 2404
Location: Townsend, Mass.
81616.60 points


1971 Chevrolet Chevelle

PostPosted: Wed Feb 15, 2012 12:57 pm    Post subject: Reply with quote

Opti spark is the issue. My friend has had 2 of these cars and issues are common with them. The aftermarket replacements are better but not cheap.
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2001 Focus 2.0 Zetec
stock cams, bolt-ons and tune
15.63@87 MPH 1/4mi

1971 - Chevelle 408 SBC N/A
6.86@102.5 MPH 1/8mi
10.78@122 MPH 1/4mi
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William Jones
Member


Joined: 30 Jan 2006
Posts: 823
Location: Lake city, FL
28541.86 points


1971 Ford Mustang

PostPosted: Wed Feb 15, 2012 3:14 pm    Post subject: Reply with quote

We put an accel optispark on it new and there is less than 20 hours on it.
_________________
Take the horse out off the barn and let her RUN BABY RUN!!!!!

92 LX 454ci Clevor 9.24@142.53 N/A
71 Mach1 454ci Clevor 10.16@134 N/A 3850lbs race weight "Lost in fire"
03 Cobra Bone stock 12.42
68 Falcon 363ci 10.55@126 N/A
95 GT 363ci 11.08@118 N/A
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10sec.et
Member


Joined: 29 Mar 2006
Posts: 3473
Location: Houston,Texas
346658.74 points


1969 Oldsmobile Cutlass

PostPosted: Wed Feb 15, 2012 4:16 pm    Post subject: Reply with quote

problem with the Opti is that it only takes one good puddle in the road to ruin your day. new or not, that Opti HATES water. has he been through any drive through car washes ? how old is the water pump ? those will leak and soak down the Opti. also seen issues with corrosion on the sensor pigtail at the Opti. are you positive its "random misfire" ? could it just be bad gas ?
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af2 wrote:
It seems we can look at our magical Balls and come up with a fix?

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William Jones
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Joined: 30 Jan 2006
Posts: 823
Location: Lake city, FL
28541.86 points


1971 Ford Mustang

PostPosted: Wed Feb 15, 2012 11:49 pm    Post subject: Reply with quote

10sec.et wrote:
problem with the Opti is that it only takes one good puddle in the road to ruin your day. new or not, that Opti HATES water. has he been through any drive through car washes ? how old is the water pump ? those will leak and soak down the Opti. also seen issues with corrosion on the sensor pigtail at the Opti. are you positive its "random misfire" ? could it just be bad gas ?


I will ask him if he has been through any car washes but he said it happened the first time after leaving our shop on the interstate headed home. The whole engine is totally rebuilt so no oil leaks or water leaks when it left the shop. The code it throwing is random mutiply misfire. When he called me I told him to get new gas in it since it was old and replace the O2 sensors since they were not replaced when we did the rebuild. The reason it seems weird is the fact that it runs great and then out of the blue it sputters and throws the code.

Bam

_________________
Take the horse out off the barn and let her RUN BABY RUN!!!!!

92 LX 454ci Clevor 9.24@142.53 N/A
71 Mach1 454ci Clevor 10.16@134 N/A 3850lbs race weight "Lost in fire"
03 Cobra Bone stock 12.42
68 Falcon 363ci 10.55@126 N/A
95 GT 363ci 11.08@118 N/A
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10sec.et
Member


Joined: 29 Mar 2006
Posts: 3473
Location: Houston,Texas
346658.74 points


1969 Oldsmobile Cutlass

PostPosted: Thu Feb 16, 2012 1:52 am    Post subject: Reply with quote

if its been dry then its time to look elsewhere. realistically, the reason the water kills the Optis is... 1. it causes crossfiring in the cap or 2. it has enough time to take out the little sealed bearing the shaft rotates on and the sensor reluctor hits the sensor itself.

i have had MAF cause misfires on mine. is the air intake still stock with that weird "home plate" looking thing on top ? mine would work its way loose and cause an air leak (didnt fit worth a damn to begin with).

silly question but, did all the ignition cables get pushed onto the dist with at least a couple "clicks" ? if the wires are missing the little metal clips it wont contact the terminals very well and ultimately burn the end of the wire and cap terminal off.

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af2 wrote:
It seems we can look at our magical Balls and come up with a fix?

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William Jones
Member


Joined: 30 Jan 2006
Posts: 823
Location: Lake city, FL
28541.86 points


1971 Ford Mustang

PostPosted: Thu Feb 16, 2012 2:12 am    Post subject: Reply with quote

10sec.et wrote:
if its been dry then its time to look elsewhere. realistically, the reason the water kills the Optis is... 1. it causes crossfiring in the cap or 2. it has enough time to take out the little sealed bearing the shaft rotates on and the sensor reluctor hits the sensor itself.

i have had MAF cause misfires on mine. is the air intake still stock with that weird "home plate" looking thing on top ? mine would work its way loose and cause an air leak (didnt fit worth a damn to begin with).

silly question but, did all the ignition cables get pushed onto the dist with at least a couple "clicks" ? if the wires are missing the little metal clips it wont contact the terminals very well and ultimately burn the end of the wire and cap terminal off.


Yeah it still has the home plate on it with a K&N filter on the end I will tell him to check the whole intake setup make sure its still attached good. We put the MSD street wires on it and installed them before it was installed in the car so I could route them out of the way and make sure they were plugged in. I appreciate the help with this. Thanks a bunch

Bam

_________________
Take the horse out off the barn and let her RUN BABY RUN!!!!!

92 LX 454ci Clevor 9.24@142.53 N/A
71 Mach1 454ci Clevor 10.16@134 N/A 3850lbs race weight "Lost in fire"
03 Cobra Bone stock 12.42
68 Falcon 363ci 10.55@126 N/A
95 GT 363ci 11.08@118 N/A
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squeeezer
Member


Joined: 02 Mar 2007
Posts: 2427
Location: new richmond WI
191524.76 points


1991 Chevrolet Camaro

PostPosted: Thu Feb 16, 2012 1:48 pm    Post subject: Reply with quote

check fuel trim under load too,when you get the chance
ive seen too many+25

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Paul P
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Joined: 15 Aug 2002
Posts: 2404
Location: Townsend, Mass.
81616.60 points


1971 Chevrolet Chevelle

PostPosted: Thu Feb 16, 2012 4:37 pm    Post subject: Reply with quote

Was there an issue like this with the previous engine in the car?
_________________
2001 Focus 2.0 Zetec
stock cams, bolt-ons and tune
15.63@87 MPH 1/4mi

1971 - Chevelle 408 SBC N/A
6.86@102.5 MPH 1/8mi
10.78@122 MPH 1/4mi
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View user's profile Send private message
William Jones
Member


Joined: 30 Jan 2006
Posts: 823
Location: Lake city, FL
28541.86 points


1971 Ford Mustang

PostPosted: Thu Feb 16, 2012 9:31 pm    Post subject: Reply with quote

I just got off the phone with him he said the MAF was a little loose and before we worked on it that there was a check engine light but wasn't sure what it was for. When we got it at the shop it had a cracked head and two bad rod bearings he had overheated it when the radiator tank cracked. So I have him checking for any vac leaks and then reseting the computer and see what happens if it continues he said he would take it and have a diagnostic check done. It only happens like once everytime he drives it. He said he will be cruising along then he tries to accelerate and it will not respond then sputter and the CEL flashes and it goes away and runs fine. It is also hunting for idle when he comes to a stop sometimes.

Bam

_________________
Take the horse out off the barn and let her RUN BABY RUN!!!!!

92 LX 454ci Clevor 9.24@142.53 N/A
71 Mach1 454ci Clevor 10.16@134 N/A 3850lbs race weight "Lost in fire"
03 Cobra Bone stock 12.42
68 Falcon 363ci 10.55@126 N/A
95 GT 363ci 11.08@118 N/A
Back to top
View user's profile Send private message
10sec.et
Member


Joined: 29 Mar 2006
Posts: 3473
Location: Houston,Texas
346658.74 points


1969 Oldsmobile Cutlass

PostPosted: Thu Feb 16, 2012 11:49 pm    Post subject: Reply with quote

definitely sounds like a vacuum leak somewhere after the MAF.
_________________
af2 wrote:
It seems we can look at our magical Balls and come up with a fix?

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View user's profile Send private message
Paul P
Member


Joined: 15 Aug 2002
Posts: 2404
Location: Townsend, Mass.
81616.60 points


1971 Chevrolet Chevelle

PostPosted: Fri Feb 17, 2012 8:20 pm    Post subject: Reply with quote

Get rid of that stupid intake muffler right in front of the motor and put an aluminum puck in it's place. That could be a source of leaks. I will post a pic of my buddies as he had issues with that too. Simple elimination of a point of failure.
_________________
2001 Focus 2.0 Zetec
stock cams, bolt-ons and tune
15.63@87 MPH 1/4mi

1971 - Chevelle 408 SBC N/A
6.86@102.5 MPH 1/8mi
10.78@122 MPH 1/4mi
Back to top
View user's profile Send private message
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