80 308 GTSi digiplex 101

The rubber hose going to each Digiplex ECU supplies the (same) absolute pressure inside the intake plenum -- (if working correctly) each Digiplex ECU will change the ignition timing based on this pressure signal (which we often call "vacuum" because it is below the atmospheric pressure) and engine RPM. You've got a good idea to try swapping the units and see if the problem moves to the other bank or not (and, yes, no need to physically move them -- just swap the connectors for a test if you can).

 

Hose connects the two digi boxes togeather, and goes to the manifold vacuum source.

 

Thats normal. It is not the muffler. Never designed to flow equal. The pipes do not have a designated bank.

 

No not at all.

I said it was not the muffler.

 

Have the mixture tested with a 4 gas exhaust gas analyzer. It should be done by someone who is familiar with the K-jetronic injection system.

Running with the mixture too lean will give that red header glow. I recently helped Birdman set his mixture to eliminate a glowing header problem.

Having 1 or more cylinders not firing can also result in combustion in the header causing it to glow.

CAN BURN DOWN:
If the header is glowing, then it's radiating enough heat so that you should be worried about one or more of the K-Jetronic plastic fuel lines melting & your car going up in flames.

 

CRANK SENSOR bad or malfunction --- bank 1/4???

I would try swapping the (2) sensors ---- see if the problem follows. If it does, replace the sensor. Make sure all the wiring and connections are good, too.

 

don't drive the car until you verify that the timing on the hot bank is not retarded. i had a digiplex failure 2 years ago and ended up frying 3 valves because the timing was retarded. it cost me $8k in tuition (total head redo), but now i know what i'll never do again. good luck, jon s

 

There are (3) of them mounted on the bell housing in the plane of the flywheel. One is for TDC 1/4, one is for TDC 5/8, and the other is for the tach/RPM pickup. When you look at the bell housing from the driver side of the car, and assume that the top of the engine is at "12 o'clock" ----- the 1/4 sensor is located at about 10 o'clock, and the 5/8 sensor is located at about 7 o'clock.

 

No special tool needed.

 

Here is a photo sent to me from another f-chatter showing the location of the sensors
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Not really, at least not without an oscilloscope --- it's an inductive device, so testing it requires a fairly sophisticated approach. The fact that it is not "open" or "shorted" (i.e., it has a low resistance continuity) indicates that is probably okay.

Often, just cleaning them up real good can solve the problem. Have you tried re-installing it after the cleaning and checking if that cures that problem? If not, it is worth a try before replacing it as they aren't cheap ---- around $175 or so a piece.

 

MARC ----

You may also want to inspect the pins on your flywheel to see whether they are canted or bent ---- because it appears as if the tip of that sensor has been scraped and damaged.

This could also just be the result of a chunk of debris that temporarily interfered between a pin and the sensor, but there have been reported cases of the pins coming partially loose and shifting out of alignment on these cars. In some cases, pins have even fallen completely out!!

At any rate, since you have removed the sensors, it's a good time to have a quick look at the pins as now they can easily be witnessed through the sensor mounting holes.

 

It's hard to tell from pictures, but they both look a bit banged up. The sensors may be okay --- they can probably tolerate a bit of damage. It's really not possible to say just by looking at them. There should not be any scraping on them though. I suggest looking at the 2 pins on the flywheel to see whether either of them have witness marks from hitting the sensors. If there are marks, the problem is with the pin(s).

Also, I understand why you don't want to risk swapping the sensors. So, you could try this -----

Re-install them in their original banks, and start up the car. Use a timing light to check on spark plug leads for cylinder #1 and then #5 ---- with the car warmed up and idling, look to see if the flywheel marks are correct for 1/4 and 5/8 ignition idle positions (the flywheel has separate sets of marks for each bank). Also, observe if the timing is stable and not bouncing around in position. If the mark for #1 is off the mark or unstable, I think you can conclude you have a bad sensor, and it should be replaced.

You say you have already replaced Digiplexes, so we can rule them out. I assume you have already looked at all the other basic things like wiring, connections, distributor caps, rotors, etc. so they can all be ruled out too? The vacuum supply to the Digiplexes is shared, so if there were a vacuum problem, both banks would be malfunctioning.

Then the only thing left is sensor or pin. From the scraping on the sensors, I'm guessing the 1/4 pin might be off alignment.

Unfortunately, I am already back in Colorado for the Winter --- I spend only Spring & Summer in Montreal. Otherwise, I would offer to stop by and help you out