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So I'm at the tail end of a long rebuild and install of an '86 turbo motor into my '85.5 NA. I'm using as many stock parts from the donor car as possible, harness, ECUs, sensors, intercooler and plumbing, etc...
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I'm running into a trademark no start "no tach bounce" scenario at this point as it's finally ready for first start. I've done a thorough troubleshooting workflow to isolate sensors and wiring issues. I have fresh Bosch reference and speed sensors and a new-ish replacement LR reference sensor harness I've used since the factory one was beyond crusty. The oscilloscope readings of the sensors are good and they're producing good consistent peak to peak voltage numbers. Good ft9 solid state DME relay, though I've tested with a jumper as well with no results. After a few days of troubleshooting it's looking likely that I have a bad DME, the one I'm using came with the donor motor, has been opened up, and obviously is nearly 40 years old. I opened it up again last night and naturally the ignition driver solder joints have cracks in them, seem to have good continuity but I'll reflow them for good measure this morning and see if has any effect.
Having a late model car, it's seemed like most of the harness/electrical stuff has been very straightforward, more or less plug and play. Is there anything obvious that I could've missed in regard to using this motor in my NA chassis? I did have to revert a change I had made at the 14 pin connector for the ignition signal to accommodate the 16v motor I had in this car last- that connector is now as it came with the original 8v motor and as far as I know I shouldn't need to make any changes there for the new turbo motor.
Anything sticking out to you guys? All sensors and checks on the standard one page DME wiring test sheet pass, other than the tach/upshift wiring at pins 11 and 21 on the DME connector, which is supposed to have continuity and does not. I realize the 951 never utilized the upshift light (neither did my car in the first place for what it's worth....), and I'm too dumb to know whether A. it's normal or B. even if it's not if it could result in a no start issue.
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Thanks in advance for any advice you guys may have. I'm trying to get back into the forum format, really hope with use this forum can take off and be a good source of information compared to the yardsale that is FB groups...
Hi, see my post in your other 'saga' thread. I'm wondering if you hooked up the tach? It's not an obvious thing to do when installing a turbo motor in a non-turbo chassis, so if you didn't put some effort into sorting out that wiring, I'm guessing your tach isn't working. Now that would not explain the no-start, but best to start with a working tach so the no-bounce doesn't throw you off. If you have an o-scope, you can also check the signal on dme pin21 when cranking. That's the signal the drives the tach (green/black). It should pulse to ground in time with the revs. If you see those pulses, and the tach is not bouncing, then the DME is working (in that regard) and the tach is not for whatever reason (probably wiring per my other post).
Thanks Tom! This is exactly the type of information I'm on the hunt for. Both the car side and the motor side of the harness have the matching red 4 pin connector that goes right together, my assumption is that the wiring is the same inside the plug but that obviously could be completely wrong. I'll try to track down the diagram for that plug.
I'll have some time this afternoon to mess with it hopefully, I'll go ahead and scope that pin 21 signal- that may actually be the nail in the coffin in regard to confirming whether or not the DME is good or not. I think If I'm not seeing tach output signal there and have since confirmed the ref/speed sensor inputs are good (they are), it may indicate something else internal to the ECU has gone south.
Also, to answer your questions in my other post- I am using the donor car's harness, DME, and KLR. Basically I tried to use everything I could off the donor in order to keep things as simple (theoretically) as possible.
Ok, quick update on this: we have tach connectivity to DME, and we have tach bounce! Er...did.
Per Tom's suggestion I double checked the wiring from the DME harness to the tach- it appears that in fact the red 4 pin plug on my '85.5 does jive with the corresponding plug on the '86 turbo engine harness. I had continuity all the way, and was able to verify tach response by grounding that pin at the DME.
Also, that morning I spent a few minutes re-flowing cracked solder joints in my DME as a last resort, the 3 pins at the ignition driver were of course the worst though still showing good continuity with a DMM. Oddly enough that was apparently a real issue, as soon as I plugged it in and cranked a few revolutions I had tach bounce! For whatever reason literally the next crank it was gone. I'm guessing the DME is on it's last legs...
Most of the time the solder cracks are microscopic, I suggest you reflow the whole dme. It is tedious but I have had success 2/2 times I did this with faulty dme's and with an alarm module too. My method is to clean off the outer pcb coating with alcohol or a special pcb cleaner would be even better and have better results then I use Kester 2331-zx water-soluble flux and Kester 24-6337-6403 water soluble flux cored solder then once all the joints are reheated with a soldering iron and solder added where necessary I rinse off the flux with water and it looks great with very shiny and clean joints.
The speed and ref signals are processed by the "S100" chip on the DME motherboard. That chip turns the raw a/c signals into square 5 volt pulses that are connected to the hardware interrupt pins 12 & 13 on the main 8051 microprocessor on the motherboard. Since you have an o-scope, you can probe pin 12 and 13 on the 8051 to see if it is getting the pulse, and pin 21 to see if the ignition signal is being generated. That might help steer you to where the problem is.
You might also try bypassing the KLR. The ignition signal makes a round trip through the KLR so that the KLR can pull timing when needed. If the KLR is bad, the ignition signal may never get back to the DME. The ignition signal goes in pin 9 of the KLR and out pin 16 of the KLR. To bypass it just short those two pins together. Factory alarms are capable of causing similar issues by cutting all power to the DME -- so worth confirming you have 12v and solid grounds going into the DME...
So I went for the "easy button" and pulled the trigger on a fresh DME from Focus 9- Joe was incredibly knowledgeable and easy to deal with. He even suggested I send him the aftermarket 55lb injectors I plan to use and he could make sure the DME is set up to run them properly. I do intend to keep this car for a long time so it seemed like a justifiable investment to run it with an ECU that's not nearly 40 years old with existing issues....
One interesting thing- when Joe was bench testing the new DME he found that my brand new LR chip I had was bad. Not sure if I did something to wreck it while it was plugged into the car or what, I'm guessing getting a non-functional chip right out of the box is relatively rare- I'm going to contact them on Monday and at least see if they can give me a deal on a replacement. I did tack weld a cat-back exhaust on the car a week or so ago with the DME's plugged in, I usually try to remember to unplug them- not sure if that would've wrecked the chip. So...not totally sure how that would've effected my no-start/tach bounce issue, but I'm assuming the car won't run if the chip is not functioning.
Crenshaw wrote: Sat Feb 03, 2024 5:48 am
So I went for the "easy button" and pulled the trigger on a fresh DME from Focus 9- Joe was incredibly knowledgeable and easy to deal with. He even suggested I send him the aftermarket 55lb injectors I plan to use and he could make sure the DME is set up to run them properly. I do intend to keep this car for a long time so it seemed like a justifiable investment to run it with an ECU that's not nearly 40 years old with existing issues....
One interesting thing- when Joe was bench testing the new DME he found that my brand new LR chip I had was bad. Not sure if I did something to wreck it while it was plugged into the car or what, I'm guessing getting a non-functional chip right out of the box is relatively rare- I'm going to contact them on Monday and at least see if they can give me a deal on a replacement. I did tack weld a cat-back exhaust on the car a week or so ago with the DME's plugged in, I usually try to remember to unplug them- not sure if that would've wrecked the chip. So...not totally sure how that would've effected my no-start/tach bounce issue, but I'm assuming the car won't run if the chip is not functioning.
Modern chips have gotten better but static (and welding) can still fry them. That said, who knows how LR handled them and/or if they ever functioned correctly. When they were selling the M-tune, they never came across to me as super well-versed in microelectronics... At any rate, I'd strongly recommend you ditch the LR chips and contact @Fast951 at Vitesse Racing. He's in a league of his own.
P.s., don't forget the KLR. It can fail in all the same ways....
So as suspected, the DME was bad- as soon as I got a fresh Sport DME from Joe at Focus 9 it fired right up, pig rich of course as it's on 55lb injectors and 3 bar fpr and all I had was a stock chip while I wait for a replacement from LR. (Which, it should be noted- Dave at LR was incredibly accommodating and offered to send me a replacement for the cost of shipping, even though I stressed that there was no way to confirm that it was bad right out of the box or if it was something I did- welding, mishandling, whatever.)
But, sure enough it will only run with the KLR jumpered, it still produces spark with the KLR plugged in but the timing is off enough to where it won't run at all. Is there a chance the KLR chip is bad? Would that produce a no start condition? The chip in there is the mate to the LR chipset I got, considering the DME chip was bad I wonder if the KLR chip was bad too... I'll try the KLR one more time tomorrow with a stock chip (have to find it first, doh!) before I condemn the KLR and begin the hunt for another one. Both the DME and KLR I have came from the donor car and look like they've been through a war....
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So speaking of which, do I even need an aftermarket chip in the KLR? I'm running a Tial wastegate and manual boost controller, cycling valve and plumbing is all removed.
Anyway, long story long- now that I know the majority of the swap wiring and setup is good, just need to button up a bunch of little wiring cleanup and other stuff and I can finally get it on the road to break in the clutch and motor.
