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Truck won't start...Mopar ECU?
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Author:  kxracer728 [ Mon Aug 26, 2013 6:57 pm ]
Post subject:  Truck won't start...Mopar ECU?
I went to start the truck this morning and it started for a few seconds and then died. I keep with my normal starting routine and the truck would not start :x it's never been this hard to start since i got the truck running so i figured i better start trouble shooting instead of grinding on the starter and creating wear in the motor

I know it's getting gas so that's not the problem...I disconnected the battery and coil and read the resistance across the terminals and got the 1.7 ohms from what i read the range is (0.70 - 1.7 ohms) then moved one of the test leads from the side terminal to the high-tension terminal in the center of the coil and got 8,600 (7,500 - 11,000) is the range on that test. So i concluded the coil was good...

I tested the ohms coming from the single pickup from the distributor and got 305 ohms. I disconnected the coil wire going to the center of the distributor and connected a lead to the negative side of the coil (with the battery connected) and then with the ignition ON i held the coil lead close to the metal frame of the truck and then touched on a ground with the negative coil lead and there was no spark coming from the coil wire. I then unplugged the wiring harness from the ECU and did the same coil test and did get a spark from the coil...

According to one of my service manuals this means the ECU is bad. I tested the voltage and ohm readings on the ECU wiring harness and they were all correct. I made sure the ECU was grounded to the frame by testing pin #5 according to the manual and got continuity (i believe this means it's grounded)

Anyway's i took the ECU i bought from o'reillys and they exchanged it for a new one since it has a limited lifetime warranty. I haven't put it on the truck yet to see if it fixes the problem but if it does...is it that common for a new mopar style ECU to go bad that fast? I've only been using it for 4 or 5 months
Author:  DusterIdiot [ Mon Aug 26, 2013 8:11 pm ]
Post subject:  Yes.
Quote:
is it that common for a new mopar style ECU to go bad that fast?
No it's not common for that to happen to actual late model EI modules. Sadly the one you got over the counter is probably a chinese knock off (as well as the versions that are the low-end modules from SMP). So 4-5 months isn't bad...this is why the move to using a Chevy HEI module is the preferred retro fit.

-D.Idiot
Author:  kxracer728 [ Mon Aug 26, 2013 8:54 pm ]
Post subject: 
The old ECU had made in china on it... i noticed the replacement had USA on it (it didn't say made in USA) so who know's? I have read that the mopar style ECU's are not reliable but i didn't know that it could be this bad :twisted: I will know if this replacement ECU fixes the problem

If it does...than yeah, i will definetly convert to the HEI ignition in the future because this thing went out without much warning!

I'm going to add an additional ground wire to this module to make sure it is grounding properly!

I'll update when i figure out the problem :roll:

Thanks D.I.
Author:  kxracer728 [ Tue Aug 27, 2013 9:47 am ]
Post subject: 
I put the new ECU on and added an additional ground wire but the truck has no signs of starting...It ran like it always has the last time i drove it so i'm not sure what happened :(

I used this ignition system test and the test light came on

http://www.youtube.com/watch?v=bl0Z6kbyI0c

I can see gas squirting into the barrel of the carb and can smell it so i know it's getting fuel

What are some other possibilities of why it won't start?
Author:  crater [ Tue Aug 27, 2013 10:32 am ]
Post subject: 
So that test makes sure power is going into the coil. What about coming out? Is it getting spark to the plugs? Have a spare coil to try?
Author:  wjajr [ Tue Aug 27, 2013 4:39 pm ]
Post subject: 
Have you tested ballast resistor? If it is not passing electricity (open circuit due to broken resistor wire) the car will try to run while key is in start posistion, and as soon as key is reliesed engine won’t fire.

Disconnect wires attached to ballast resistor, and test for contenuity.
Author:  kxracer728 [ Tue Aug 27, 2013 7:58 pm ]
Post subject: 
I tested the ballast resistor for continuity and it had 1.4 ohms...i went ahead and bought a new one and put it on i'll keep the old for a spare...the new one tested at 1.6 ohms. I'm getting close to 12 volts coming from the starter relay to one side of the ballast resistor and close to 6 volts from the resistor going to the positive side of the coil. I'm getting about 1 or 2 volts on the negative side of the coil

I went ahead and bought a new coil even though the other one tested ok they both test about the same 1.7 ohms (side terminals) close to 9,000 (center, side terminal)...

I pulled the distributor cap to take a look at the air gap (i bought a brass feeler gauge when i bought the coil) and i could see the gap was a lot bigger than the .006 the manual says it should be...i loosened the screw to adjust the air gap (after bumping the reluctor around were it lined up as best as i could get it) and noticed that there is probably about at least a 16th of an inch play in the pickup piece even with the adjusting screw tigtened down (You can move the pickup coil piece back and forth). Is this normal? I tried to adjust the air gap to.006 and the truck STARTED but was running rough and i could here the pickup making contact with the reluctor (especially when you gave it some throttle) so i shut the truck down and backed off the air gap a little bit but could not get it to start again. I pulled a plug and was not getting any spark at all so i'm wondering if the pickup coil is the culprit? Since the voltage readings on the ECU, ignition coil, resistor are good...

I'm getting about 310 ohm reading out of the pickup coil coming from the distributor

I will take some pics of my setup and inside the distributor tomorrow so you can see what i'm working with...
Author:  wjajr [ Wed Aug 28, 2013 5:38 am ]
Post subject: 
Quote:
I tested the ballast resistor for continuity and it had 1.4 ohms...i went ahead and bought a new one and put it on i'll keep the old for a spare...the new one tested at 1.6 ohms

I went ahead and bought a new coil even though the other one tested ok they both test about the same 1.7 ohms (side terminals) close to 9,000 (center, side terminal)...
Those are good numbers, same goes for coil it’s in the ball park. Often coils test good when cold, but once heated after engine has been running they sometimes develop an internal short after many duty cycles; but this is not the case as your machine won’t start.

All Mopar owners stock a spare resistor in glove box; it’s the law, Murphy’s that is, that spare on hand will prevent its use.

Quote:
I'm getting about 310 ohm reading out of the pickup coil coming from the distributor
That is a good number.
Quote:
.i loosened the screw to adjust the air gap (after bumping the reluctor around were it lined up as best as i could get it) and noticed that there is probably about at least a 16th of an inch play in the pickup piece even with the adjusting screw tigtened down
This is not good, once gap is set and set screw tightened down pick-up should not budge. Is the slop coming from bad bushings holding distributor shaft not the pick-up, in other words is the reluctor moving in relation to pick-up?

Have you removed the distributor to the bench for better access and viewing, or has adjustments been made with distributor installed in block?

You need to figure out why gap won’t stay constant. Once that problem is fixed truck should run.
Author:  kxracer728 [ Wed Aug 28, 2013 11:01 am ]
Post subject: 
Quote:
Is the slop coming from bad bushings holding distributor shaft not the pick-up, in other words is the reluctor moving in relation to pick-up?
The reluctor and shaft have some up & down play but it does not move in relation to the pickup plate...the pickup plate has play up and down and some side to side it's definitely not held down to stay in one position.

Quote:
Have you removed the distributor to the bench for better access and viewing, or has adjustments been made with distributor installed in block?
I'm getting ready to pull the distributor (this will be the first time i've ever done it) i have manuals to help guide me...my main concern is to find TDC correctly. I haven't made any adjustments to the distributor in several months

When i bought the truck the kid before me was using this distributor with vacuum advance with the lean burn module and he didn't cap off the vacuum pot and left it open i assume this means it was sucking air when the truck was running i don't know how long it was run that way (i haven't run it like that)...i removed the lean burn and started using the vacuum canistor with the electronic ignition. I don't know if this may have contributed to something coming loose or not i've been driving the truck about 400 miles a month for the last 4 or 5 months about a month ago i started putting some highway miles on it...

My plan for finding TDC is to pull all of the plugs and turn the engine until i see the 2 timing marks line up with 0...i believe on the vibration damper that there are other single timing marks (not sure what for) but the one with marks on both sides of the damper are the ones to use for TDC. Then i will check to see if the rotor is pointing at #1, then i will take the oil filler cap to look at the valves (i believe they are suppose to both be closed and the rocker arms should be loose) this truck has the hydralic lifters does this still apply?

I think that i'm going to get one of the 30-3690 distributors from o'reillys and replace this distributor and may keep this one for rebuilding if everything else looks good. I looked on ebay and saw that you can buy new pickup plates that are not too expensive...

When i put the new ballast resistor on i used a round rubber washer behind a metal washer to help keep from tightening it too tight and breaking the ceramic body. Since it's ceramic i don't think it has to be grounded to the frame? You'll see in one of the pics

Here are some pic's

Image
Image
Image
Image
Author:  wjajr [ Wed Aug 28, 2013 2:00 pm ]
Post subject: 
Quote:
.the pickup plate has play up and down and some side to side it's definitely not held down to stay in one position.
That is normal

One of the plates moves as vacuum is applied to vacuum advance diaphragm. This how additional advance is achieved over and above base timing, and mechanical advance.
Quote:
I'm getting ready to pull the distributor (this will be the first time i've ever done it) i have manuals to help guide me...my main concern is to find TDC correctly.
Keep this simple, before loosening and pulling distributor, with cap & plug wires removed, make note, mark, or photograph where the rotor is pointing for a reference. As distributor is pulled the rotor will turn counter clock ways due to its heliacal gear. Just as it comes free make another mental note where rotor is pointing. Remember while distributor is out, do not roll engine over or your reference point will be moot, and you will have to go through the finding TDC dance; = PIA.
Quote:
When i put the new ballast resistor on i used a round rubber washer behind a metal washer to help keep from tightening it too tight and breaking the ceramic body

I would mount it as the factory did directly to body sheet metal. The reason is that resistor gets hot, and all that metal acts as a heat sink. Just snug up its mounting bolt.

Hereis one place to get Chrysler stile wire connectors.
Author:  kxracer728 [ Wed Aug 28, 2013 8:22 pm ]
Post subject: 
I put a new distributor on...and it started and ran 8) i had a neighbor help me with the TDC he held his thumb over the #1 plug hole while i turned the crank with the belt until we got to TDC on the compression stroke...

So, the play in the pickup coil plate was the problem...i noticed that after replacing the distributor that my timing marks were'nt jumping around like they use too, they are steady now! They use to jump between 6 and 10 degrees, i thought that it was slack in my timing chain but i guess not

Thanks wjajr for your help on my past 2 problems...i still need to adjust the timing a bit. But it will be interesting to see how the truck performs on the road now that my timing and spark is more stable. Fortunately, it wasn't a major motor melt down :D and the slant 6 will be back on the road soon :wink:
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