Hi Fellow slanters, It seems the second time the engine died, the ECM was not bad. It checked out fine with ACcel. They have driven it on one of their test vehicles, and it seems to be OK. So there is probably something not right in the harness. I did muck with this by way of shortening it physically on some of the leads to fit the slant instead of the universal SBC V-8 configuration, so maybe I have done something that is causing this problem. It seems as if Rance's advice to use the dual sync harness, and jury rig it for UIP use is a possible source of problems here as well..

The question is, why did it run for awhile, and then die? I don't know if Fred did a diagnostic check the second time. They might have just ASSUMED, it was the same failure as the first time, when they did find a bad transistor. That thinking seems very reasonable, even though possibly wrong. Now the task is to look for shorts in the harness that could either put it into a safety shut down, or be of an intermittent type, that only showed up after awhile. The thing that seems the most likely is an intermittant short in the ignition harness between the pick leads and ground, or another disruptive, but not deadly voltage source. . I have asked Fred to simply cut the ignition leads out of the harness, and run them as their own seperate harness, that is isolated from everything else.

Another possible culprit could be the Electronic spark control or ESC, which is supposed to retard timing if there is pre-ignition. This is not currently hooked up, but is just hanging there unused. Since it does interface with the ignition in some way, possibly that is a source of trouble. There is an NOS circuit, that I will never use, that is hanging there unused as well. I have asked Fred to just cut this out of the harness, and get rid of it as well, since there is a 12 volt and a ground lead in there that could be possibly causing a problem.

I actually do not feel as discouraged as I did before. I have had time away from it, and a few good people thinking about the problem at hand, and the info that the ECM is OK, which means that if we can find the problem in the harness, we are headed to home here.

I will keep you posted.
Sam

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Hmmm, well there's some progress there.

Whenever I build/modify a wiring harness, I make sure to take an ohmmeter and check for continuity from one end of a lead to the other end where that wire is supposed to be in the connector/pigtail. Then I check every other lead to make sure there is open circuit with the first one. This takes some time, but it will save you headaches later. For the MS harnesses, I spent probably 20 min checking this.

--> Insert probe into one end of wire, check other end of that wire with other probe, then check every other wire for open circuit on the other end. Lather, rinse, repeat...

Lou

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Home of Slant6-powered fun machines

I agree with Lou here.......I had an unpleasant experience with this in the spring when an apprentice where my vehicles are serviced messed my EFI wiring on my truck. They spent hours (un invoiced) trying to track it down. I spent 3 hours splicing in a new harness and lathering and rinsing ......no further problems.

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Yeah....Im the one who destroyed this rare, vintage automobile.....

Is there a "stimulator" equivalent for accel computer? Or maybe build your own test bench from spare parts and your own harnes, use noid lights for injectors and something to spin spare distributor for pickup... it will take a bit of work to do it from scratch but at least you will have a way to verify ecu operation without getting accel involved.

Glad there is some forward progres. Your goin to go nuts once you find the little strand that escaped the terminal shorted against something else and is wreaking all this havoc.

If you have a vom with an audible ohmmeter on it, then I highly recommend using the audio function as you test for intermittent shorts.

Connect the leads of the vom to the two connections you suspect may be intermittently shorting, then wiggle the harness. The audible tone responds much faster to an intermittent short than an lcd display will. Your ears will tell you what your eyes miss.

It should be noted that this test will not reveal high-resistance-path short circuits. The alarm tone will not sound above (I believe) about 2000 ohms. But most shorts in automotive wiring are not of this type (with the exception of carbon tracking in high voltage ignition wiring).

-Mac

Thanks for the tips. I am sure the entire forum is listening to both problems and solutions here. I have a question that one of our resident geniuses can likely answer. Since the car ran both times for awhile, it might be that the problem in the harness is temperature related, and didn;t cause a problem until the engine got warm. Does the resistance go up or down as the temp sensors heat up. If it goes down as they heat up, and there is a short between the ignition pickup, and one of the temp sensor feeds, then there would be a ground that was not made until the sensor heated up, and the rsistance lowered enough to complete the ground circuit. This might have damaged a weak ECM part the first time around, and simply killed the pick up read the second time around.

With only two wires to the sensor, and one of them going to ground, it seems as if temp sensor input to the ECM must be between a source voltage and the sensor. How else could the voltage change from the sensor with only two wires, if one of them is to ground. Anyway, think about this and see what you come up with.

Unfortunately, or maybe fortunately, (I don;t know for sure yet), I am not working on this car at all myself. It is at Total Performance, and they are doing all the testing, and diagnostic work. I hope I don't have a heart attack when the bill comes due. The good news is, I don;t think they will deliver a product back that they do not trust. He has a sense that I am trying to hold the cost down by doing the little clean up things to detail it after he gets it running, so he knows this car is not just a rich boy's toy, but a hobbyist project. So, I think he will call me and talk about things if it looks like the cost is getting very high. many of the ideas put forth on this forum ahve been passed on to Accel through Fred, so your input can be quite helpful. Thanks again.
Sam

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Well, to tell the trutch I was hoping to here better news than this. But it could be alot worse as you say.

As far as the harness it is just going to have to be tested to know if there is shorts.

Temp sensors have two types, one that just goes closed curcuit which is like touching two wires together. This type can be used for triggering relays or such for fan control. The other vairies the resistance & the computor sends voltage threw it & retreives it to know what temp the engine is. But unpluging what you have hooked up to any temp sensor could eleminate any shorting caused by having the wrong sensor or a miss wiring.


The NOS curcuit you should keep intack instead of cutting it out, it could be used for something else latter on after you get this all behind you.



ESC - This confuses me. Is there a module that is not wired in yet ( I dont see why it would need it). Or is it some wiring that is not wired in yet. If so I think this is the wiring you should of been using because you are setting it up as a Computor Control setup letting the DFI control timing but the MSD controling spark. If I am understanding correctly you just anwsered the whole problem. It states in the manual that if you do this wrong the DFI will close the ignition curcuits drivers to try and protect itself from burning out. Which goes along with it starting but then shuting down.

I can not know for sure without knowing exactly how you have the system wired, Coil,MSD, Dizzy & DFI <----- Just ignition curcuit on the DFI part. If you could get this info I could anwser that question pretty quick.


Jess

did you ever dig in my disregarded by most of the people "electronic interference" theory? some electronic equipment can fail like this due to interference. I don't have the theoretical knowledge to back up my hunch, just have seen lots of quarks like this before.

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Juan Ignacio Caino

Please use e-mail button istead of PM'ing. I do log in sometimes but I'll be answering quicker thru e-mail.

Sam - you can check out typical GM temp sensor curve at http://www.slantsix.org/articles/dibias ... ersion.htm - goes down as temp goes up. The temp sender circuit is a simple voltage divider - the ECU passes a known constant voltage (say +5v) through a known resistor value, which is in series with the sensor, and ground. It then measures voltage at the point between known resistance and unknown sensor resistance to ground. From there, using ohms law, calculation of the unknown resistance is simple.

I doubt the current is shorting through the sensor itself - those thermistors don't handle much current and chances are you probably would of popped the sensor before the ecu.... esp seeing as the ecu should have safeties built into it (but you did say previously that accel said this wasn't the first ecu they've seen burnt in same manner?)

Start at the higher current stuff, main battery feed, fuel pump, injectors, then work way towards ecu. Other things related to temp - fans, iac motor/solenoid...

Pierre has got it on the sensor, and I really think that's a very remote, if not impossible, cause - high T shorting, that is.

Any way to swap in a new harness? Might be time to start over on that. Checking continuities should be first.

Lou

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Home of Slant6-powered fun machines

Lucky 13, would you answer a couple of questions here regarding this passage?

Quote" ESC - This confuses me. Is there a module that is not wired in yet ( I dont see why it would need it). Or is it some wiring that is not wired in yet. If so I think this is the wiring you should of been using because you are setting it up as a Computor Control setup letting the DFI control timing but the MSD controling spark. If I am understanding correctly you just anwsered the whole problem. It states in the manual that if you do this wrong the DFI will close the ignition curcuits drivers to try and protect itself from burning out" Unquote

What manual are you reading? Can you give me links or tabs to flow through to where you read this. If you do "THIS" wrong. What "THIS" are you refering to. You are right, if I knew what THIS you were refering to, that could be the answer since it is indeed shutting down the ignition.


Sorry I do not know how to use the quote feature here on the forum. Maybe you can walk me through that.
Sam

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Sorry for the slow reply, I have been at the Doctors office all day. I can go back and get the Info I had found. But you can also hook the computor up to the internet that you have the DFI software on for tuning ( laptop probably) and hit F1 or F4 or one of the buttons ( I will go back and find out which one) to take you to all there wiring diagrams & info, maybe more info than is available other sources.


There was two differnt ways of hooking up to a VR dizzy with MSD. One way took into account that you was going to let the DFI control the timing. The other way was for hooking up for letting like a MSD or what ever you was using control the timing.


The way you are ( or should be) trying to hook up is refered to as (Computor controled timing) or something like this. I will go back back & go threw all the info right now. But this ESC you refered to sounds like what would have been the wiring for Computor Controled Timing setup. In which case is what sould have been wired up instead of what may have been wired up. There is just so many possibilties in the problem you are having that trying to diagnos over the internet is almost a joke. But with the DFI coming back as being good this makes it better.

All the wiring is a bit confussing on this unit. Its like they tried to make it to where you would almost want to use all there add on stuff like Spark modules & adaptors and such because it is the best documented wiring they have. Let me just go dig all the ifo back up & I will coming back with a wiring diagram as to the way I think it needs to be wired. I will probably have to wright it out instead of it being a true diagram though but it will only be the DFI Ignition,MSD,Dizzy & coil part of it..... Then you can have it checked to see if this is the way it is wired.


But in a nut shell there is two Ignition curcuits on the DFI, if you use the wrong one for the application Accel states that it will Close the curcuits off in the DFI on both ignition curcuits to try and protect itself from blowing the curcuits. So it would fire up and then shut down, sound about like what is happening.


Just wandering, in the other post I linked you to or told you where there was a Diagnostic flow chart for checking the DFI ignition curcuit. Was these test ever run? They are in the info I was talking about, I will get it also.


Sorry if my post above sounded like implying anything in a wrong nature. Not the intent, only to help find the problem is its intent.


Jess

Ok, one thing they are calling the Connector for the Knock Sensor a ESC connector. I guess this is what you was speaking of as not being hooked up. It shouldnt cause any of your problems unless maybe it has to be Shut down in the DFI software and this not being done some how would shut the spark down. That would be odd but I guess its possible.


The extra documents Accel meantion is suppose to be accessed by Hitting Control F1 when you have the laptop hooked up to the internet
( computor with calmaps installed on)

I went back & looked at some of the post from the other thread & you had described the wiring. It sounded correct but the wire colors where wrong & I wander if this is where the problem could be. Here is a diagram with the colors of the way it appears it sould be wired.

http://webpages.charter.net/jess1313/DF ... WIRING.bmp



I hope I did that right so that you can see it. I tried to just post it as a pic but I dont know how all that works yet on this forum. Seems to be a bit diff than others.

When you try to crank the engine over, does the DFI show a crank sensor signal when cranking, Or give a RPM reading in the software?[/url]

Hi Lucky, I do have the MSD wired just as it shows there. To answer Argentina, there is a plan to get the UPI pickup shielded better, and isolated from any source of magnetic interference. Since the distributor is by necessity right near the spark plug wires, they could have been being showered by radiation energy. I think Fred plans to route the pick up wires downward, and away from the spark plug wires in general, and bring it up the firewall. If he cuts the pick up wires completely out of the harness, as I suggested, then that should eliminate any internal harness contamination or interference. It sure seems like the UIP leads must be where the trouble is. It seems as if other wiring shorts or bad grounds would simply cause it to run poorly because sensors were not picking up correctly, but would not shut things down completely.Sam

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Your idea on the other sensors being shorted is pretty much correct. Although there is always the strange problems that happen sometimes.


The easiest way to know if the Dizzy signal is working properly is to go into Calmaps in View mod & wail cranking it should show around 125 rpms. If it does not show this then the signal is goofed or just not getting there. If it shows RPM then the Dizzy curcuit is working.

If it shows no 125 rpm signal then first thing tighten up the air gap on the pick up in the Dizzy as tight as you can get it without it touching the reluctor. Then if no RPM signal check wiring going to the DFI from Dizzy & check for open wires or shorts to each other or ground. Which at this piont should be known for sure if they are good or not already.

Look at the color of the wires that go to the DIZZY, they are different than what you had posted before although the C & D location you said would be right but it is still not the colors you had posted that are suppose to be going to the Dizzy , maybe something wrong there maybe just different color wires. But the wiring I find said they are Tan with a black strip & Tan with Blue strip. Not a Black wire & a Grey wire as you had stated in the other thread.


Ok, if still no RPM get Osilating scope & it should show 4V on the signal coming from the DIZZY. If at least 4V volts is what it shows good. If none of this gets you a RPM reading in Calmaps go back and make sure the setup in the software is correct. It should read RPM if all this is right.

But if all is setup right & working but no RPM check for 12V at the L3 wire at the DFI WIAL CRANKING THE ENGINE OVER. It should show atleast somewhere close to Battery voltage on this curcuit when cranking over.

If it has voltage here, then take the Scope & check to see if a Signal is comeing from the Blue EST wire (the one going to the white wire at MSD). You should be getting a trigger from this wire when cranking over. If you are not getting a trigger, check for 9V at the plus side of Coil when cranking. If 9V is not here then check the Pink VIGT wire that goes to MSD and see if it has close to Battery Voltage wail cranking over. If it does have voltage on Pink wire make sure MSD has good Main Power/ Ground hookups. If they are good and all things above are correct MSD is goofed on the curcuit that feeds the coil. Which I doute very much because you said you caould ground the white wire & it would make spark.


If all this is happening this way there is only one thing that can be wrong and that is that it is not setup right in Calmaps, even though you may think it is. Or possibly( he he, that makes two things doesnt it) some of the POWER or Grounds That the DFI is suppose to have (including ones that it should have in cranking mode) is not being supplied.

But if Calmaps shows RPM, Blue EST wire sends signal, Coil has nine volts while cranking, MSD will make spark when white wire is struck to ground, And Calmaps is setup properly & you have a Known good Coil, & all the Cranking possition power is there and all other Power/grounds is there, you should have spark. And I hope that a known good Coil wire & Dizzy cap is being used.



Hope this helps because it hurt my brain getting this down in right order just right.




Jess Good Luck