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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.
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 flashes constantly, and 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?
Does the tach bounce when you crank the motor? (If not, think speed/ref sensors, harness, DME, etc. -- i.e., upstream of ignition components.)
Does the dash boost gauge show "1" with the ignition on and car off? (If so, it confirms the KLR and probably DME are getting power.)
Which VR piggyback do you have, and have you confirmed the Wasted Spark installation? There is some interfacing in the harness and piggyback set-up needed to get it right, and your blink tests would make me want to review closely. Contact John at VR if unsure. When I ran VR's wasted spark, it took some work with John to get it glitch-free.
Running a stock chip with MAF and big injectors won't work (well). The VR chip is actually a mini-computer and is not likely the cause of intermittent dropped spark. Certainly way less likely than the configuration of the wasted spark. You could, however, revert to the factory ignition with the rest of the VR stuff in place, to isolate if the issue is related to the wasted spark.
It's also a 35 year old car, so any number of harness, ground or sensor issues could be the cause. Sorry it's being a pain. It's got to be something, so keep after it and you'll get there.
yep. same here. Years ago I had the same issues, could never really track it down. Tried changing all and various sensors with no effect. I finally changed the KLR out with another and "seemed" to make a difference. I still suspect that the harness running to the coil may be suspect. Anyway running VEMS now, but that's another story.
I understand you've done the re-solder thing... but I'll just add that your symptoms describe pretty much exactly what I had while back... solved with re-soldering, particlarly these two joints (cracks seen in pic)
M’Guinn, sorry to hijack this thread, I was reading your response and I have a question. I have had an S and currently have an S2, but recently also acquired an ‘87 951. Being that this car is new to me, I have a question about the boost gauge. When my power is on but engine not running the boost gauge stays at 1. When idling, it drops to .3 or .4, then spikes above 1+ when the throttle is revved. Is this normal behavior? Also it seems that the needle is very quick to move and “jump around”, not a smooth controlled arc. Does this sound normal as well?
M’Guinn, sorry to hijack this thread, I was reading your response and I have a question. I have had an S and currently have an S2, but recently also acquired an ‘87 951. Being that this car is new to me, I have a question about the boost gauge. When my power is on but engine not running the boost gauge stays at 1. When idling, it drops to .3 or .4, then spikes above 1+ when the throttle is revved. Is this normal behavior? Also it seems that the needle is very quick to move and “jump around”, not a smooth controlled arc. Does this sound normal as well?
Normal, Ignition on motor not running you are @ Atmoshphere… = 1 bar Engine on, No throttle engine is under vacuum= LESS than atmosphere = Less than one bar...
Rev the engine turbo spools bit over one bar.. Get a load on it driving and make some Boost! Over 1 bar... So on the factory Gauge 2 bar is actually 1 bar of BOOST....
Also.. note that 0.4 on the gauge is aprox. 15-17 in hg of vacuum; at fully warm, ideally you are showing at least that or less (ie. under the 0.4 line). If you are only showing 0.3 or less vacuum fully warm (remember closer to 1 is less vacuum), you may have a leak(s).
If you've ever seen a regular vac gauge hooked up to one of the lines, you'll see how they jump around fast with changes in throttle!
PS Tom M'Guinn makes and sells a device that alters your dash gauge to read boost only ie. making 1 actual 1. This is useful as it gives a more accurate measure above 1... esp if you increase boost and want a quick view!
Does the tach bounce when you crank the motor? (If not, think speed/ref sensors, harness, DME, etc. -- i.e., upstream of ignition components.)
The tach definitely moves when I crank the engine during no start, and I really don't think it's the speed/reference sensors or their wiring harness, because they were installed and checked by one of the best 944 specialist in Western Washington just a couple of months ago, but I suppose anything is possible.
Originally Posted by Tom M'Guinn
Does the dash boost gauge show "1" with the ignition on and car off? (If so, it confirms the KLR and probably DME are getting power.)
I don't recall. I'll have to check this next time I'm out there.
Originally Posted by Tom M'Guinn
Which VR piggyback do you have, and have you confirmed the Wasted Spark installation? There is some interfacing in the harness and piggyback set-up needed to get it right, and your blink tests would make me want to review closely. Contact John at VR if unsure. When I ran VR's wasted spark, it took some work with John to get it glitch-free.
My piggyback is SMT6. I believe the Wasted Spark was originally installed properly and functioning properly for a period of time. The wasted spark was installed professionally by the same 944 specialist who did the rest of the work. Also, if I remember correctly from the PO he drove the car about 1000 miles since all the Vitesse products were installed in 2016 (I have to double check that date).
Originally Posted by Tom M'Guinn
Running a stock chip with MAF and big injectors won't work (well). The VR chip is actually a mini-computer and is not likely the cause of intermittent dropped spark. Certainly way less likely than the configuration of the wasted spark. You could, however, revert to the factory ignition with the rest of the VR stuff in place, to isolate if the issue is related to the wasted spark.
It's also a 35 year old car, so any number of harness, ground or sensor issues could be the cause. Sorry it's being a pain. It's got to be something, so keep after it and you'll get there.
That's good to know that chip likely isn't the problem, so I will just swap it when I try another DME. Speaking of which I just bought a DME/KLR from a wrecked 86, so when those arrive I will test the car with them.
I understand you've done the re-solder thing... but I'll just add that your symptoms describe pretty much exactly what I had while back... solved with re-soldering, particlarly these two joints (cracks seen in pic)
Good luck
Thanks for the picture. I'll open the DME back up and check those joints.
gpr8er, I am hoping a new computer can solve it for now and I can keep rewiring the engine off for a while, but with a 30 year old electronically controlled car I know it's somewhere in the future.
Also.. note that 0.4 on the gauge is aprox. 15-17 in hg of vacuum; at fully warm, ideally you are showing at least that or less (ie. under the 0.4 line). If you are only showing 0.3 or less vacuum fully warm (remember closer to 1 is less vacuum), you may have a leak(s).
If you've ever seen a regular vac gauge hooked up to one of the lines, you'll see how they jump around fast with changes in throttle!
PS Tom M'Guinn makes and sells a device that alters your dash gauge to read boost only ie. making 1 actual 1. This is useful as it gives a more accurate measure above 1... esp if you increase boost and want a quick view!
Jimbo, yeah if I remember correctly my truboost reads around -10 at idle.
I also just stumbled upon this regarding Lindsey Racing M-tune/MAP, and it says that you have to disconnect one of the resistors in the DME in order for it to work properly and it was the resistor that was disconnected in my DME. Is this something you need to do for Vitesse MAF or is this just a MAP/LR thing?
Jimbo, yeah if I remember correctly my truboost reads around -10 at idle.
I also just stumbled upon this regarding Lindsey Racing M-tune/MAP, and it says that you have to disconnect one of the resistors in the DME in order for it to work properly and it was the resistor that was disconnected in my DME. Is this something you need to do for Vitesse MAF or is this just a MAP/LR thing?
Both. I believe the circuit is used for the map sensor. So it must be cut. Its actually a dead circuit from the factory that is used by these vendors to back feed the dme.
Progress has been slow, but I have finally had a chance to start looking into my intermittent spark problem again, and have been able to run a few more tests. I hooked an o-scope up to the speed and reference sensor just to rule them out and they were well within spec per Clark's garage. I also checked the new to me, tested DME/KLR for cracked solder joints or any other signs of damage and they looked prestine, so I cut the necessary resistor and swapped the chips. I thought this solved the problem I got a solid 15 minutes or so back and forth down the road, which is the longest I've been able to drive. Then right as I was about to pull out for a longer test run the car lost spark. Since, then I've pulled the wiring harness apart a bit more and confirmed the installation of the wasted spark on the DME/VRPB side. I also verified all of the grounds to the DME and went through about half of the VRPB wiring. I am thinking my next steps are to go through the engine bay wiring harnesses and finish checking the installation of the VRPB. However, part of me thinks that maybe there is something wrong with the Vitesse wasted spark computer with the way the red LEDs flash. Even when the car is running the LEDs do not flash as it says they should in the instructions. I included a video of the LEDs while the car is running and while the car is not consistently sparking to see if anyone familiar with wasted spark has any thoughts. If someone knows a way to test the computer I would love to know how, if not I'll get in touch with John and see if he can help me test it after I have ruled out all the wiring. Finally, while going through all of my Vitesse docs I found some info about the coding plug and about how out of the box a removed coding plug is for pump gas and an installed plug is for race gas. However, after installation you can make the plugged/unplugged tune whatever you like correct? So, my car, which has the plug installed and has only ever been run on pump gas, could still be running a safe tune with the plug installed, right? I am also going to hook up the VRPB to my computer next time I test drive it to see if maybe the piggyback can give me any insight into what the problem may be.
Video of the car running. The upper right LED flashing concerns me.
12-30-2019, 03:34 PM
Intermittent Spark
