Idle problem.Thought fuel, but it was bad ECU

-
adriver

adriver

Blazing Apostle
Joined
Jun 1, 2007
Messages
8,900
Reaction score
5,818
Location
Where the red fern grows
A little back-story on the Dart.
This car is a driver. So when I built it, I went for reliability and street ability. . Some time around 2000 I got a Diplomat cop car with 39K on it.
I pulled the 318/360 engine, lock up transmission and 8-¼ rear from the cop car an put them in the Dart.
I like spread bore Q-Jets, so I took off the electric one that came on the cop engine and put a junkyard GM one on it instead.
(I run junkyard Q-jets with modified Mopar style throttle levers on the base,)
This car has been driven coast to coast and back. And for the last six years I’ve been putting 80 mile a day, five days a week, on it as a commuter.
Some day I’ll get my oil change records and figure the miles.

So for a while now, the Dart’s had a issue with the idle.
Not a problem for driving since, I’m on the interstate most of the time and just keep my foot in it when it has acted up at the traffic lights.
I figured it was something in the carb idle circuit.
Funny thing.
It would be OK sometimes and sometimes it would sort of have trouble idling and then pick back up.
Or idle up and drop down.
Like something was clogging the idle bleeds or something.
I’ve taken the carb apart clean it and checked everything more than once.
Well, last week the car died on me just before I got on the interstate and then it died while actually on the interested. It restated both times.
But that did it.
Yesterday I went through the whole fuel systems.
New fuel pump. (Stock of course).
Even dropped the tank for a peak and it looked pretty good for the age.
The new fuel-sending unit I put in there in 2003 was OK.
No clogs, trash or gunk.
Not finding anything in the fuel system, I started checking the electrics.
I started swapping the ECU and that did it.
When I built the car long ago, I got a junkyard Orange box.
That must have been almost 15 years ago. It was fine then.
The thing must have deteriorated over the last few years.
When I put other ECUs on the car yesterday for testing, not only did it idle like new.
But the Idle speed picked up and I had to tweak the screws back down. And it is smooth now. It was sort of lumpy before.

Lesson of the story is to check your ECU if you have an idle problem
Weak spark at idle (sometimes) I guess. It was trying to warn me.

I tried both 5 and 4 pin types for testing.
You know, they say a five pin won't work on a single ballast set up. But swapping them around for testing, I didn't have any problem. Both worked.

Oh, and I've got to check my mileage.
The fuel gage didn't hardly move driving today.
I know it's better.
Maybe I'm going to get 50MPG now.:cheers: (ha)
 
I would suspect a marginal distributor pickup situation or bad connection, IE

marginal reluctor gap

poor magnet, etc in the pickup

poor / corroded connections in the connectors

So far as 4/5 pin you cannot tell by "looking." You must check continuity of the 5th pin, as some 4 pin boxes (I have several) still have the 5th pin physically in place
 
Yes, the reluctor has crossed my feeble mind. Think a new one is in order? I wonder if a new one is made over seas now? Quality?
I had a 340 Challenger with an MSD box. I'm trying to remember the details of the problem. Can't recall exactly. Years ago. Think it worked till the box got hot.
But I do remember part of the trouble shooting. The system would run on an orange box. But the MSD would not run on the same "brand new" system on that one.
Plug one in, no work. Plug the orange in, worked.

Thanks for the pin suggestion. Gotta get the fluke out.
Since simply plugging in a new box made all the differance on this car I'm hopeful.........
 
Well,,, youre probably not going to get 50mpg.:D
I would like to commend you on posting the problem and your findings.
People that are new to this need exactly these kinds of posts.

Thanks for taking the time to do so.
 
Thank you too.
I checked back because I wanted to add one thing about the symptoms.
The way the car was acting really threw me.
It ran fine otherwise.
But when I would come off the interstate or maybe down a long road I had to be ready to keep my foot on the gas when it stopped and got to idle speed.
I would "feather" the peddle for a moment till it would run.
For lack of anyting else, I kept thinking "dash pot".

That and the other weird thing I said about it would be sitting there idling and the thing would act like something was making it slow down speed up.
This had been going on for a while. But what got me going on it was the thing just died one day. But it restarted and I got home.

It really is purring now though. When I put the drivetrain in from the cop car, I put a new oil pump, timing chain and valve seals in the engine. So it may outlast me.
If I knew someone local I could pull the engine and give it to for a rebuild I could trust, that's the way I would go someday.
I don't have the time or equipment to do that. (or experiance) I'd farm it out.
Not something I want to be in a learning curve on.
 
Good for you. You fixed it without going too far. Not a bad idea to throw an extra "good" ecu in the glove box or trunk. tmm
 
My emergency kit.
Goes with me every where in a Chrysler.
It all fits in the case.
(Those are wiring diagrams)
I figure if the key switch goes, I can piggy back it at the steering column and get going.
I actually had a dist cap go bad on a four banger Honda Civic long time ago.
I've converted to manual steering and brakes to simpliy things on the belts, etc.
Starter, battery and alternator are time change items.
I'm counting on the engine and trans to get me there.
 

Attachments

  • IMG_20120619_104833 (Large).jpg
    152.3 KB · Views: 300
I don't see a distributor in that kit, which is something I'd add.

Years ago, some of the imports used a RADIO SUPPRESSOR resistor IN the rotor!!!! Friend of mine's sister (cute little gal, too!!) was dead on the side, no spark to plugs. We found a scrap of wire, pulled a strand out of the bundle, and wrapped from the rotor contact to the cap contact to get the thing going. !!! POS !!!

Mopar never used these in /6 or V8 cars, but rotors CAN "punch through" and carbon up inside.

Looked like this damn thing:

d728_1.jpg
 
You know, that's something to consider. I'm haulling around a cap and rotor already.
I could eliminate those and just carry a whole dist.
And now that I think about it, this car hasn't idled "good" for 5 or 6 years or longer maybe.
Not the symtoms I've described. But as I'm recalling just not good.
(I was running a different GM junk yard Q jet till the last 2 years. So that was different.)
But maybe it was the box all along. Cause it idles so smooth now it's sort of scary.
I can't tell it's running. (Ha).
Just wanted to report 21 mpg this week.
Is that respectable for a 40 year old car that will keep up with anything on the road, as they say?
 
Thanks for the excellent and helpful post. I also wouldn't have suspected the ignition, since ignition problems usually first show up at WOT at low speed, where cylinder pressure is higher and thus harder throw a spark, at least my experience with my 2 Mopar minivans.

Great kit. I do similar, but not as organized. I always keep the old fan belt in the spare tire well, along with old radiator hoses and a length of heater hose and clamps, points to swap back from electronic ignition, plus a spare module, jumpers to hot-wire the coil and actuate the starter, a small carb to swap my TBI. I am tempted to carry a mini-starter, but my 64 & 65 auto cars can actually be push-started (rear pump). I have only had to call for a tow a few times in 30+ years of driving, usually my newer Mopars - timing belt pulley bearing (twice), plastic pwr steering pulley disabled serpentine belt.
 
AD, if yo decide to toss that box, I'd like to do some tests on it, if you feel like shipping it to me
 
For reference.
Didn’t I read that a 4 pin would work on a 5-pin system? Thinking about it, of course it would.
If the extra (high ohm) resistor has now been wired internally to the box.
Some people probably know this already.
But I’m doing a refresher course on it.
I sure have driven this car more than I’ve worked on it.
(I was off a little on my commute the last six years. It’s only 74 miles a day. But hey, I've made side trips.)

So, 4 and 5 pin “factory” boxes?
A long time ago, I got several off of cars in the junkyard but didn’t really spend much time wondering about it.

Out of curiosity, I went to Advance Auto Parts today.
All they sell is 4 pin boxes. Surprise!
Asked for one for a 73 and a 4 pin is what they show.
So what we do is just plug the “new” 4-pin box in if you have an “old” system and ignore the extra resistor circuit.


I was flipping through Larry Shepard’s Mopar Engine manual on this and he said there were like five different single resistors not to mention different coils.
OY VEY!
But all my single resistors check at the same ohm.
I’m thinking 1 point something it was.


I just remember that I got an orange box in the junkyard for this car and it worked (fine at the time)
About the same time back then, I had a brand new orange one fail on my Challenger and had to replace that one.
(What do they call that on electronics? “Burn in” to see if it fails?)



67dart
Are you going to do a “post mortem”? Does it involve a scalpel or sharp "sonic" screwdriver?
PM me an address and I'll mail it to you. Just please, let us know on the thread if you find anything interesting.
Doctor Who?
I've been watchig the new BBC series on netflix. I'm hooked.
Just watched "Daleks in Manhattan" while eating lunch.

It's hot outside, but I'm now going to go outside and change my wiring and run a hot wire off the starter solinoid for starting the car like it's supposed to have.
 
On the 4/5 pin

You can not tell by looking. Many 4 pin boxes have the 5th pin, so you MUST use an ohmeter on the 5 th pin to see if it's hooked to anything.

Also, I found an article that shows one of the original Mopar boxes had one pin GROUNDED. This is NOT TRUE of many of the late model (and cheap) 4 pin aftermarket boxes

I've never tried running a 5 pin box with only 1 resistor. You might "ohm" out the pins to see, maybe the darn thing is a 5 pin? Or did I misunderstand you are using a dual resistor?

In any case, yes, I'd like to tear it down and try to determine the cause.

Some of these have softer IE silicone like potting material that can be peeled out. Others are more of an epoxy, and it would ruin the box

I'll PM my address if you decide to send it over.
 
67dart

(I've gone back and edited this post this morning to correct something. This morning I'm rechecking. The coil HAS been getting 12 volts on starting after all. My bad. The prints show a splice BEFORE it gets to the resistor for that purpose. And my meter confirms this. I ASSUMED the 12 volt starting connection to the coil was at the resitor. OOPS.)



The “spare” boxes that I have are all 5-pin boxes aftermarket boxes. Old ones from the junk yard in various cosmetic states.
I did hook a couple of these 5 pins up when I was trouble shooting last Saturday and they did run very well with single ballast in the circuit.
So like you indicated previously, they must be 4 pin boxes internally.
Either that or there is voodoo magic I haven’t heard of.
I’m carrying those two "five pin" boxes in my “kit”.
And again, they do have 5 pins.

But it was HOT outside. I actually got a Fluke meter out and was going to start investigating the pins. But to heck with that. They work. I watered the lawn instead at dusk.

If you want to look at the orange box, do pm me an address.
No problem.
 
adriver,
67Dart273 is our resident auto electronics expert. He has been studying the Mopar ignition boxes for a few years, pulling them apart for death forensics and reverse engineering. A noble cause, that helps us all, and great automotive design archaeology.

Many FABO guys who just want to "get er done" and don't care about originality have converted to the superior GM HEI module that doesn't require a ballast and lets you run a better coil. To each his own. I am in the HEI camp, but my Mopars are all 1960's models so no conflict over originality. Any e-ignition beats mechanical points.
 
Bill,
See my "correction" to yesterday's post re the starting voltage.

Conveting to HEI sounds good. But I've already got tons of spare Moparts.
Sounds like work. ugh.

Yea, Mopar was a little late into high energy. Just hoping that this "experiance" of mine will help someone that is working on an orginal system.

One thing I don't want to do is get stranded with some stuff I can't get at the parts store.
I had a Challenger with an MSD fail. That motor really needed the extra spark though.
But what to do if you're between Hahiara and Bugtussle?
So I put a Chrysler box in it too for back up. Ran everything through a terminal block on the firewall. I kept prints to tell me which wires to swap over to run the Chrysler box.
 
BillGrissom said:
. He has been studying the Mopar ignition boxes for a few years.
Click to expand...

Bill, you're 'mbarassin' me agin. I've only actually gotten a few apart. Some were heat damaged, and had little "to tell." Others are epoxy potted, and are VERY difficult to diagnose and dissect. And now that my arthritis is getting worse, it gets more difficult.

I was hoping though, to discover if this box is really 'mis triggering' as I have not run into that being an "in box" problem.
 
adriver said:
For reference.

Doctor Who?
I've been watchig the new BBC series on netflix. I'm hooked.
Just watched "Daleks in Manhattan" while eating lunch.
Click to expand...

Lord Have Mercy! Why is it that Dr. Who is so addictive? BUnch-a Geeks.

And Netflix...I gotta cancel it because that site has put me up to abt 5 hrs of TV per day now!
 
You must log in or register to reply here.
-

Back
Top