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ECU? / Injector Problem

Hi All,

Well, my rebuild of ????/2000 is so close to completion I can hardly stand it. I thought I had reached the finish line a couple weeks ago, but upon starting her up, discovered that cylinder #4 wasn't firing. Troubleshot it to discover that that spark is good, fuel is getting to the injector, and the injector is getting some sort of signal, but fuel is not getting through the injector. Tried other known good injectors, still no dice.
Finally pulled the ECU and discovered the Capacitor problem in full view. A friend who repairs bizjet avionics for a living cleaned the board and soldered new capacitors in. Still no worky. #4 injector is not spraying fuel.

AARGH.

Can anyone shed a bit of light on what I might want to check next? The car is a bone stock build '91 with no mods.

Can anyone offer a nice diagram of the ECU motherboard, so that we can test the track for #4 cylinder's injector signal?

Thanks in advance.
Daver
 

Rausch

Well-known member
Joined
Dec 21, 2004
Messages
12,049
Location
Cleveland, OH
Have you swapped oput hte injector with one that is known to function?
 

cspetros

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Jul 19, 2008
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512
Location
Port Norfolk, VA
^^/ubbthreads/images/graemlins/uhh.gifQuote:
Tried other known good injectors, still no dice







The injector portion of the circuit is on page 149 above. Check the condition of the wiring harness connector, just to be sure. Good luck /ubbthreads/images/graemlins/smile.gif.
 
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toybreaker

iconoclast
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Apr 30, 2006
Messages
3,581
Do you have a spare injector resistor pack that you can swap in?

I've had one check okay with a meter, and fail under the load of firing an injector.
 

Rausch

Well-known member
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Dec 21, 2004
Messages
12,049
Location
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Quote:
^^

Quote:
Tried other known good injectors, still no dice



It appears you hae found the limit of my multitasking abilities..... /ubbthreads/images/graemlins/banghead.gif

Sry. plz continue.
 

cspetros

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Location
Port Norfolk, VA
Quote:
It appears you hae found the limit of my multitasking abilities.....


Just keeping you in line, Fluffypaws /ubbthreads/images/graemlins/wink.gif.

Daver, let us know if you fix this, in case others have the same problem.
 
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Brilliant, friends!

Time to geek out on those wiring diagrams (a special thanks to cspetros for going the extra mile and posting those!) for a while. I'll report back in a few days. Right now, I'm ready to go postal on the Nile Black lump that's been darkening my workshop for the last year and a half. I've hidden most blunt objects temporarily.
...

No, I don't have a spare injector resistor pack to swap out/test. Ehmmmm - what (and where) is that? ???

Thanks for the assistance so far.
 

toybreaker

iconoclast
Joined
Apr 30, 2006
Messages
3,581
Thanks to Cspetros for the pic! /ubbthreads/images/graemlins/applause.gif



The injector resistor pack is a small rectangular silver box mounted to the firewall.

It takes a single power feed, splits it four ways, adds some resistance to each leg and sends the results out to each individual injector.

When one leg goes bad, you get a symptom very similiar to what you are describing.

It's a quick test to plug a new one in, providing you have a spare.

Another valid test is to plug your ecu into another car and verify the problem stays with the car or stays with the ecu.
 

As you can see from the diagram just above, each injector is driven by the collector of one of the large transistors bolted to the heatsink. In most cases where there is acid damage, the issue is between the collector of the transistor and the output pin of the ECU. So, simply ohm out each collector to the rear pins, and figure out which one is open. You really *should* remove the heatsink and clean up all the acid, or your problems are only going to come back in the future. Damage to this extent really requires someone more experienced with DSM ECU acid damage repair, so you should send it to SteveP or Terry Posten for proper repairs.
 

UPDATE 6/15/2009

Well, it was a productive weekend. Obtained and swapped out a injector resistor pack (thanks again, Steve), but that turned out to not be the problem.

Then I was able to borrow and install a known good ECU. The car now runs very smoothly, on all four cylinders. Cracked open the suspect ECU that my friend had repaired, and sure enough, hiding beneath the heatsink: acid damage over several tracks. Time for some loving care from a Mitsu ECU expert! (Let's see... where is Posten's e-mail add'y again???)

The best news is that I now know my VR4 is back from the dead! It's been off the road for over five years, sitting in a field for three of those years, and in my shop for two. It was mis-diagnosed initially as a burnt valve which took it off the road back in 2004, the symptom of which was... dropping a cylinder, wouldn't you know. In actuality, it was probably the darned ECU all along, another classic case of capacitor acid discharge and damage. However, the rebuilt head and new head gasket can't hurt, not to mention all new belts and T-belt, plugs and plug wires, filters, a new O2 sensor to replace the crispy one that we found in it (it looked like it had been in the car for all of its 162,000-odd miles), and a newer 14b to replace the one with the huge, 3mm thick cracks through the exhaust housing.

Now to get it to pass Smog Check II here in Northern California, and then you'll see a stock Nile Black '91 patrolling the Modesto area.
 
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