AO

Just out of curiosity... when you jumper 1-3-5 and crank the engine, should the wires start smoking?

Well that's what just happened. Of course, I immediately pulled the jumper and turned off the ignition. Wires look slightly damaged.

I double checked the wiring diagrams to ensure I had indeed jumpered 1-3-5. I had. I'm guessing I found the issue, but what would cause this to go whacko like this?

Bill Ball

!!!!
I could have sworn it was 1-3-5, but look at this... Boy, am I embarrassed.

Bill Ball

So, that's not the explanation of your basic problem.

Anyway, the jumper for the IMS is from the inputs A1 and A2 to the output 87. I have always seen and quoted 1-3-5 as the corresponding plug connectors. That sure looks wrong, unless the plug numbers changed from 89 to later years. The 89 wiring diagram does not show the plug numbers. Here's the 89 diagram. The previous one was from the 90MY wiring diagrams

Bill Ball

Andrew: I was clearly wrong. I was so certain, too. Egad. Hopefully the brief short didn't worsen things. Let me know. I'm putting on my dunce hat. I'm headed out to the garage to see if I can wreck somebody else's car.

jon928se

I'll clarify this for the electrically challenged.

With the fuel pump relay jumpered, you should have +12V on one (and only one) pin of each disconected injector connector relative to ground. (ie connect the black lead of your dvm to the engine block)

If you can measure with the connector still plugged to the injector you should see 12V on both pins relative to ground. If you see 0V either the harness is shorting to ground somewhere or there is a break somewhere.

AO

Thanks Bill, Thanks John.

I pretty much gave up after I let the all the smoke out of the wires. Don't know yet if there's any significang damage - don't think so. I will try the 2-4-5- jumper instead. The funny thing is I was looking at the wiring diagrams just before I tried the jumper - you know... "Trust, but verify." and I was concentrating so much ont he 1-3-5 that I didn't even see the **BRIDGE** note. Obviously, I was stupified when I looked at the diagram becasue I went ahead and did1-3-5...

Oh well... I 'll try again tonight.

SwayBar

Andrew, I am an expert on this due to having to track down a similar problem on my car, and this is the quickest way to diagnose the problem:
My wires broke right after the plug at in the bend which redirets the wires back to the main loom. It is very easy to see to broken plastic insulation and the exposed wires underneath.

Don't waste your time with the Ohm meter, yet. Just do a visual on the bends in the injector wires right by the plug.

Bill Ball

Yes, those bends are good suspects. I'm amazed there aren't more shorts there as I see them all twisted up on almost every car, and after years and years of being that way, I leave them alone, if there are no cracks. Those are easy to inspect. Still, you wouldn't believe what I've found hidden under the rubber boots.

928drvr86.5

+1, when i did my intake this spring i found 3 injectors with insulation gone on both wires right at the end of the boot, i would start looking there.

Right now i am working on a replacement injection harness for my 86.5 that will utilize Hi-Temp corrugated split loom rather than the rubber tubing that was used by the OEM supplier, this will make any wire accessible along the length of the harness. You wouldn't believe the crappy construction I found when i removed the sheathing from an OEM harness i bought from a fellow lister for this project. On this harness (and probably yours) they basically pigtailed the 12V and pulsed grounds for the injectors, which is fine, but they used heavy duty shrink tubing ONLY to make the connection. That's right, wires held together and then shrink tubing over to make a connection-not a drop of solder. And obviously it's a connection of major importance where changes in resistance are a factor. I am just about as impressed with their abilities to cable-form the harness as well, I.E. wires too long and wadded up inside the sheating, rat's nest inside of the 25pin LH and EZF connectors, totally exposed(no sheathing) on the last few inches of the sheilded cable for the flywheel mag-pickupwhere it plugs into the sensor, etc.

AO

Here's an update:

I jumpered the IMR 2-4-5. I've peeled back the sheathing on every injector but have not found any cracked wiring. I swapped out the crank position sensor (I know it doesn't affect the injectors, but thought I'd do it just in case). I've swapped out the LH, fresh relays (but have used jumpers too).

The wierd thing is that both yesterday and today the car ran for about 2 minutes and then it just stops. With the use of a noid light I've determined that the injectors are not firing. I let the car cool down completely while I worked on getting mycar ready to pull the engine, and it will not re-start. I'll try again in the morning just in case it's related to somehting getting hot.

I checked to see if all the injectors have 12+ and they do.

So... this has to be a ground switching problem, right? Is there anything that I may have overlooked that would cause ALL injectors to go down?

worf928

Diagrams show that injectors are grounded through MP IX (if I read them correctly) which is the ground point under the throttle cable pulley. I have seen a case where an incorrectly routed LH-harness allows this ground wire to be sawed-on by the throttle cable.

Otherwise, I would ask what was touched on this car just prior to it exhibiting this behavior?

AO

Ahhh.... thanks Dave. I'll take a look back there. The car did this 3 years ago and was then parked, so it's unclear what it was doing before this.

SwayBar

That's a good one. Actually, there are two grounds, one for each injector bank, where one ground is grounded with one bolt which holds down the pulley-plate, and the other bolt of the pulley-plate grounds the other. One of my bolts were loose once, causing the engine to start randomly cutting-out at around 6000 RRM; it felt/sounded like I was hitting the rev-limiter!

Tampa 928s

With my 86 I found after replacing my Inj the wires under the boots (2) were shorting. After fixing this issue I found Pin 13 of the LH not contacting the connector correctly causing it to go on and off.
I unloaded all the Inj's and LH and measured from any Inj to both the 12v and Ground and from 12v to Ground, to make sure the Inj harness was not shorted and the connections were good. The ground fires all the Inj at the same time so any open or short will show by moving your harness while testing. You should measure each Inj around 17 Ohm's if I remember correctly to make sure one is not shorted. Other than a relay this will put to bed any cable issues. It took a lot of to find these two issues but this worked for me.
Good Luck

worf928

Yep. That's why I asked Andrew about previous work. If the response was something like "fuel pressure regulator replaced" then bingo! you've got a place to look for something that was not put back together right. Or, if it was 'front end body work' then it would be final ignition stages.

Now, out of curiosity, trying to reconcile what you write below with the diagrams and my memory...
If you mean the ground point near the other head (MPVIII?) then that, too, is what I always thought. However, last night, looking more-closely at the diagrams the right side is labeled as "engine electronics" and the left side is labeled as "engine power." And the diagrams don't seem to show that the ground 'splits' for each bank to the two grounds points. 'Course ground always wins and the harness itself may not look like the diagrams. And no matter which is correct, if MPVIII is loose, $h+t ain't gonna work right

Here's a picture for folks that may not have BTDT.