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Intermittent Spark (Read 382 times)
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Intermittent Spark
Dec 30th, 2019 at 7:15pm
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The issue: I recently bought an 87 951 with an intermittent dying issue. The car will almost always start cold and idle. You can turn it off and restart it and it will general idle with out issue. However when the car is driven it will randomly die and be impossible to start for about 10-60 minutes. Sometimes this is as soon as I turn out of the driveway other times it can go on a 30 minute trip and be fine. I have determined that during this time the car is loosing spark. Sometimes the car will fail to spark at all but often it will alternate spark/no spark at about 2 second intervals. Causing the car to fire for a second, but not start. Also, their are no fuel problems. The fuel pump always runs properly and I have good pressure at the rail, never less than 50psi.

The car: This problem would likely be a lot simpler if my car was stock, but it is pretty heavily modified. Here are some basic engine specs:
  • 2.5L
  • Vitesse Stage 3 Turbo kit
  • Vitesse MAF
  • Adjustable FPR
  • Upgraded injectors
  • Vitesse Wasted Spark
  • Vitesse chip/ piggyback
  • Millage Cam


Diagnostics Performed: In August prior to my ownership the following work was done:
Replace Speed/Reference sensors and harness (by local 944 Specialist)
Rebuilt ECU by Specialized ECU
Following this work the same mechanic who did the above work spent over an hour of shop time, based on receipts and PO, checking/cleaning all engine connections and grounds.
Now, for what I've done:
I checked the DME relay. I tried 2 brand new ones and the one in the car, this made no difference.
I bypassed the factory alarm with jumpers, this made no difference.
I opened up the DME and found several cracked solder joints and a resistor that had one lead completely disconnected! I have receipts and a sticker proving this DME was rebuilt less than 6 months ago, so it seems like they definitely did a pretty poor job. I re-soldered all joints and was sure I found my problem, but the problem still persisted.
Next, I pulled the KLR and I cleaned off a very minor amount of flux and corrosion, but overall the board looked pristine. The problem still persisted.
Now, I tried getting the car to die and no start, then bypassing the KLR by jumping pins 9 and 16. This made no difference, this likely rules out the KLR.
  
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Re: Intermittent Spark
Reply #1 - Dec 30th, 2019 at 7:21pm
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I also tested coil secondary and primary resistance and both tested good.
This left me with investigating the Wasted Spark module. I pulled it apart to check the board and found a minor amount of flux which I cleaned up, but ultimately the board looked good.
I then referenced the installation instructions for the wasted spark, which has a test protocol using the external LEDs on the module. My green LEDs that give diagnostics on power to the module were good. 3 solid and 1 flashing. However, my input/output (red LEDs) did not check out. My upper 2 red lights are supposed to initially blink the rightmost functions properly, but the leftmost one remains on constantly. Then the bottom 2 red LEDs that should flash alternatively do so only when the engine is getting spark. However, this diagnostic is supposed to work to test function after only the control module has been installed and the distributor and original coil are still in place, i.e. it tests if the DME is telling it to spark. This tells me that the problem must originate behind the wasted spark module. I checked all of the splices used to install the wasted spark and they all checked out. This leads me to believe that the problem lies in my DME and that I need to get this one rebuilt by a better shop and/or get a new one.

Is there anything else it could be that I'm missing? Anyone else have similar intermittent spark issues? Also, since this car is heavily modified with a custom tune can I test the car with a DME running a stock chip? If not is there a way to test my Vitesse chip to ensure that it is not causing the problem?
  
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Re: Intermittent Spark
Reply #2 - Dec 30th, 2019 at 7:53pm
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The chip itself would not cause your issue. If there was a issue with the chip it would be all the time. If you have the Vitesse piggyback you should be able connect it to a laptop and see what is going on.

DME will cut ignition due to cracked solder joints, bad caps or resistors.

Piggyback could be getting a bad signal and cutting ignition as a safety failsafe.

Your symptoms definitely sound electrical but I am not sure what the cause is. You may try contacting John at Vitesse to see if he can point you in any direction.
  

Steven Manfre Sales Manager 1501 nw 22nd ct  #10 Pompano Beach,Fl 33069 Toll Free 866-944-7883 Local 954-968-3766 www.944online.com
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Re: Intermittent Spark
Reply #3 - Dec 30th, 2019 at 9:57pm
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This post only rooted here for alternative publications.

'Rogue Ant' has a paper written at Lindsey Racing based on coil adaptive solutions and describes the functional spark timing.
The wasted gate spark might be in it or not. It does have explanations about timing load and such for sizing the coil is a file might be accessible in the search finction black tool bar above.

It has been a couple years since reviewed.

Since it is close to New Years and you might be awaiting the test proceedure for 944 Turbo Service Test Plan out there. DME_KLR Test Plan. Pdf is another possibility you could access after considering the Steve/ 944 online statement.

After looking at the drawings for an 87 in Factory Manual number 4 it appears a lot is tied to timing of injectors so the basis of your guidance is well appreciated. As well since the piggy/back Steve pointed to would be a Vitesse rep question.
The timing trigger from KR at DME pin/plug 31, TD input final stage from KR pin/ plug 32 could be checked as a matter of reasonable scope definition.
Where the post above Steve 944 Online ask without quoting is basically Anyone else .... Having these issues... reviewing the 85 DME_KLR Test Plan. PDF it does recommend a timing issue. As well at the DME pin/ plug 3 Full load signal from KLR might be different on the 23 MB file too big to get in and attach.

" Heavily modified" caution to readers of your post warrants respect to your 87 and informative well written post.

EDIT:
http://roguetuning.com/944951_ignition
Cannot seem to get the link in but the above is close if you desire a close rendition of diagnosing coil and pulse trigger.

« Last Edit: Dec 31st, 2019 at 3:37pm by anchor »  

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Re: Intermittent Spark
Reply #4 - Jan 3rd, 2020 at 12:44am
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XxSteve944onlinexX wrote on Dec 30th, 2019 at 7:53pm:
The chip itself would not cause your issue. If there was a issue with the chip it would be all the time. If you have the Vitesse piggyback you should be able connect it to a laptop and see what is going on.

DME will cut ignition due to cracked solder joints, bad caps or resistors.

Piggyback could be getting a bad signal and cutting ignition as a safety failsafe.

Your symptoms definitely sound electrical but I am not sure what the cause is. You may try contacting John at Vitesse to see if he can point you in any direction.


Thanks for the info. It's nice to know that I shouldn't have to worry about the chip being bad. I will definitely check all the piggyback wiring. I will also try to hook up the piggyback to my computer to see what's happening. I just need to get a disc drive so I can install the software.

I also just bought another DME and KLR from a wrecked 86, so I will swap the chips and computers to see if it makes a difference.
  
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Re: Intermittent Spark
Reply #5 - Jan 3rd, 2020 at 12:53am
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anchor wrote on Dec 30th, 2019 at 9:57pm:
This post only rooted here for alternative publications.

'Rogue Ant' has a paper written at Lindsey Racing based on coil adaptive solutions and describes the functional spark timing.
The wasted gate spark might be in it or not. It does have explanations about timing load and such for sizing the coil is a file might be accessible in the search finction black tool bar above.

It has been a couple years since reviewed.

Since it is close to New Years and you might be awaiting the test proceedure for 944 Turbo Service Test Plan out there. DME_KLR Test Plan. Pdf is another possibility you could access after considering the Steve/ 944 online statement.

After looking at the drawings for an 87 in Factory Manual number 4 it appears a lot is tied to timing of injectors so the basis of your guidance is well appreciated. As well since the piggy/back Steve pointed to would be a Vitesse rep question.
The timing trigger from KR at DME pin/plug 31, TD input final stage from KR pin/ plug 32 could be checked as a matter of reasonable scope definition.
Where the post above Steve 944 Online ask without quoting is basically Anyone else .... Having these issues... reviewing the 85 DME_KLR Test Plan. PDF it does recommend a timing issue. As well at the DME pin/ plug 3 Full load signal from KLR might be different on the 23 MB file too big to get in and attach.

" Heavily modified" caution to readers of your post warrants respect to your 87 and informative well written post.

EDIT:
http://roguetuning.com/944951_ignition
Cannot seem to get the link in but the above is close if you desire a close rendition of diagnosing coil and pulse trigger.



Thank you for the heads up on the resources I will have to check them out. I'll also have to investigate the timing trigger and associated wiring.
  
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