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Can anything be done to stop the missfire/pop

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#21
Ron Alan

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Jim,

 

Are you also looking closely at each clip...both male and female...both wire terminations and contact points?


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#22
Jim Drago

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Yes, I am going to reinstall this harness in our dyno mule and see if I can pin point.. Besides these splices, I am still thinking of female ends on the cam position sensor. The other sensor and connectors all have pigtails and wiggle room, but the cam position sensor mounting directly on the valve cover, the wiring harness plugs directly into it. So it makes sense that a break could occur there.

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#23
steveracer

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I was researching making a new harness a few years ago, but lost interest when I hit 27 different color/stripe combos.


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#24
ChrisA

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Jim, I had the ground wire to the MAF break within the insulation about an inch before the plug. Took a while to isolate where the problem was after we determined it wasn't the sensor its' self.  There could be lots of issues with this harness. Not good seeing all those splices, particularly the 1 into 3 power line & 3 into 1 grounds that all use the same gauge wire, just not good design at all. Crimp connections of themselves are not necessarily bad if they are properly done.


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#25
Jim Drago

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Jim, I had the ground wire to the MAF break within the insulation about an inch before the plug. Took a while to isolate where the problem was after we determined it wasn't the sensor its' self.  There could be lots of issues with this harness. Not good seeing all those splices, particularly the 1 into 3 power line & 3 into 1 grounds that all use the same gauge wire, just not good design at all. Crimp connections of themselves are not necessarily bad if they are properly done.

 

The crimps do look good, no corrosion, no tarnish, nothing loose. The 5v refrence goes 1 into 6, the grounds splice afm, cas, cps into one, then join a six way ground connector ( white plug)

Jim 


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#26
AW33COM

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Watching the Miller video I would not rule out other components besides the harness.  It's strange that a wire stops working for a fraction of a second on the straight away, and then it works.  I would understand it, if it was during cornering, where leaning of the car connects/disconnects something.  Though cookie, and I have no idea how to reproduce this. 

 

Faulty ignition switch could cause this behavior as well. 



#27
dfuser

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Well, my problem I had in my car at the NASA nationals never got fixed.  I pretty much replaced every sensor and the main computer.  I ran the final race with it missing.  The same problem cam back to life at the run-offs with Michael Ross driving my car.  Its seem to come in after the car been running for a while.  I am assuming at this point somewhere with in the harness the wire is broken.

 

I am in the process of building quite a few new ones.  Trying to finish sourcing all the connectors and fixing this crimping crap the Jim has shown us.

 

Bill


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#28
dfuser

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Also engaging into the 1.6L Harness as well.  Looking at possibly about 6 months before the 99-00 are available, 


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#29
Tom Hampton

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Watching the Miller video I would not rule out other components besides the harness.  It's strange that a wire stops working for a fraction of a second on the straight away, and then it works.  I would understand it, if it was during cornering, where leaning of the car connects/disconnects something.  Though cookie, and I have no idea how to reproduce this. 

 

Faulty ignition switch could cause this behavior as well. 

 

 

I've been an electrical engineer for a long time.  I've built a lot of stuff.  The life of living breathing electromechanical things is not nearly so simple...especially things that move and live outside (planes, trains, and automobiles).

 

There are a thousand reasons things can happen besides the simple "its a broken wire/loose connection that pulls apart under G-load".  Quite frankly the "g-forces" of cornering just aren't that significant to "wire".  The impulse G loads associated with bumps, and resonant vibrations are much more likely to cause harness related issues---these aren't related to cornering in any way.  As the engine revs during acceleration, a resonant frequency can be setup on a length of suspended wire that causes a break to pull apart momentarily.  But, as the engine rpms continue to increase the resonance goes away...until the next gear (maybe). 

 

Poor grounds are frequently a cause of mysterious behavior---particularly the high resistance variety.  High resistance in either power or ground can cause all kinds of weird stuff under electrical (not mechanical) load...that can be really hard to replicate in the shop.  Floating (not connected) or intermittent grounds can be devilish to troubleshoot (as noted by ChrisA above---the inside the insulation variety is pretty common, but no more enjoyable). 

 

Verdigris corrosion on bare copper in crimps, thermal expansion of crimped connections, use of dissimilar metals (causing a form of corrosion), improper wire guage can all cause large resistance changes.  Most of these are exacerbated with age, and more crimps equals more opportunities for problems.  Connectors have insertion lives...they are designed for a certain number of connect/disconnect cycles.  After 20 years, and the above average number of disconnects on a racecar, the sockets can stretch, the pins can wear...making poor mechanical, and intermittent electrical contact.  Pins and sockets can get dirty.  Pins and sockets can push back in the connector when mated, and then pull forward when un-mated.  I hate these, because everything looks normal when you inspect it, and it only "fails" when connected.  Again, these usually work fine sitting still and intermittently disconnect under mechanical and thermal loads.

 

High(er) frequency signals, and higher voltage/current/power signals are generally the most susceptible to these types of issues.  Eg, ignition systems in cars. 

 

Its not a hard and fast rule, but wiring harnesses are MUCH more likely to cause intermittent issues than components.  Components usually just stop working in one way or another.  Unless you can isolate the intermittent behavior to a specific component (based on some very well informed judgement), you should start with the wiring.  Only once you've eliminated the wiring only then return to the components. 

 

The inspection details above don't do anything to alleviate the suspicion that it is the wiring harness.  To the contrary, they support the theory.  My money is still on the harness. 


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#30
Randy Thieme

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... Connectors have insertion lives...they are designed for a certain number of connect/disconnect cycles.  After 20 years, and the above average number of disconnects on a racecar, the sockets can stretch, the pins can wear...making poor mechanical, and intermittent electrical contact.  Pins and sockets can get dirty.  Pins and sockets can push back in the connector when mated, and then pull forward when un-mated.  I hate these, because everything looks normal when you inspect it, and it only "fails" when connected.  Again, these usually work fine sitting still and intermittently disconnect under mechanical and thermal loads....


 

A few years ago my 1.6 would die intermittently.  The fault was the connection to the ECU.  I had recently swapped ECU's temporarily.  The other ECU had some of its pins twisted slightly, I presume to make better contact in the other harness.  When that ECU was inserted into my harness it enlarged some of the sockets permanently.  Then when the original ECU with straight pins was put back in the contact became intermittent.  Fortunately a very good auto-electrician found the issue and was able to replace the bad sockets.   No problems since then.



 


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#31
dfuser

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Note:  My specific issue came to life after an engine swap.  After talking with Jim Drago we both believe the problem is in the Harness however most likely somewhere within a plug at the connecter side.  Most likely the CAM sensor plug itself. 

 

I have watched my videos and when my miss starts, my shift LEDs all turn off and then come to life at once. 

 

This happened to me once before with the fan connector.  The pins inside the connector from the harness has spread far enough they were making intermittent contact.

 

Hopefully Jim can fix his issue that way.  My car is still not back to test that theory.


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#32
AW33COM

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I have watched my videos and when my miss starts, my shift LEDs all turn off and then come to life at once.

 

Where do you get your power from for that shift light?  It must be post ignition. 



#33
HoneyBadger - BrianW

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Where do you get your power from for that shift light?  It must be post ignition. 


My experience tells me that he is more than likely loosing the rpm signal and not the power. Electrical issues cost me the Tuesday morning qual session at the runoffs this year. I noticed that on my dash I would loose rpms on the dash, but not power.
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#34
dfuser

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Where do you get your power from for that shift light?  It must be post ignition. 

From the connector behind the dash cluster.


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#35
Joe (dad) Jordan

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Also engaging into the 1.6L Harness as well.  Looking at possibly about 6 months before the 99-00 are available, 

Thank you Bill!


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#36
Adax

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I included this link on my build blog but for those of you not reading...

 

This site has great information regarding motorsports wiring. It's of course not legal or affordabe, but good info here none the less.

 

http://www.rbracing-...wiring_ecu.html


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#37
dfuser

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One of the options I can add, is a connector at the fire wall, however, I want to make sure that it will be legal by SCCA/NASA before I can offer that option.   This will simplify ENgine swaps and harness issues at the Engine side. 

 

And of course the added cost!


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#38
RussMcB

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I noticed the following in the SCCA GCR:

 

On 96-05 cars a single fixed bracket may be installed to support and secure the crank position sensor (CPS) in its stock location. The bracket may only attach to the CPS, the CPS mounting bolt, and the closest oil pump threaded mounting hole and must serve no other purpose.

 

Was that inserted because there was a problem with the original mount?


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#39
Jim Drago

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Russ
The CPS was an after thought on these engines. It is held in posiition by one 6 mm bolt. There is no locating pin etc. IMO, it should be two bolts or one bolt and a locating pin of some sorts. They often come out of adjustment and if they do, the car doesnt run any longer. I put one on my STL car, but dont run them on the SM car. But we do loctite the bolt and check the gap often
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#40
tynor

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Reviving this thread.

 

Is anyone marketing an SM-legal CPS "bracket"?   I had a CPS related stumble when testing my new (to me) '99 SM.  The sensor was pretty loose when I checked it.  Have readjusted the sensor and loctite'd the bolt, but it still feels pretty iffy.  As Jim says, no locating pin - just relying on friction to keep things in place.

I've googled and don't see any of the obvious sources marketing a CPS brace or bracket - surely that's not true?
 


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