Rebuilt CDI box and poor running

[jwmarc]

My 1987 930 hesitated and died while driving a month ago...Thought it was the infamous yellow fuel cutoff relay ( happened twice before).The car would not restart.. initially checked CIS potential issues with fuel pumps and other electrical relays supporting the system. Got the pumps working with a jumper wire and still no start.

Checked the spark and there was none. Checked the green trigger wire and the coil. Considered the CDI as the culprit and sent it out for a rebuild. The main capacitor and a snubber capacitor were bad.

Re-installed the CDI unit and was able to get the car started, re-set timing as best I could, had to deal with some backfires and eventually got the car able to start and run on idle without dying out.

The problem is the car bogs down under load and backfires if revs are brought up to quickly. The car really runs poorly beyond idle.

I am at a loss for how to proceed to address the poor running.

- I plan to check fuel delivery pressures ( original pumps)
- Does the warmup regulator have voltage during ignition and during warm-up ( i didn't see power on a lead)?
- Nor do I have voltage at the aux air valve during initial start and cold running- shouldn't I?
- Since the car starts ( spark) I suspect that the CDI box is working properly..but during rev up and load up the car runs very poorly and backfires. The CDIs voltage output based on RPM does decrease with increased RPM. rebuilder said this is how it's supposed to work.
- If the triggering of the CDI box works at idle could the triggering system be breaking down under load and messing with the spark distribution?
- The car ran perfectly before the breakdown which must have only been the CDI spark issue.
-I did disconnect the Lambda box Amphenol connector and the two relays under the seat were inspected for bad solders...so that was about the extent of troubleshooting and I don't know if disturbing these devices may be contributing to the poor running.


Any help would be greatly appreciated.
Thank you.

[908/930]

Pretty sure the WUR and Sup air valve should have power, looking at a wiring diagram I have for a older car it shows they are both fed from the same wire, pin 10, red-black/yellow, on a diagram from a 1986 it only shows the WUR on terminal 14 of connector t66.

If your WUR is not heating up that will make it run rich as the engine warms up, does it run ok for first 5 or 10 seconds?

[Kraftday]

May consider replacement of the coil at same time as CDI box.

[908/930]

I just checked the voltage on the Sup air valve on my car and with ignition ON it shows no voltage, did not start it as it is sitting up on my lift at the moment. SO not sure what triggers the relay to supply voltage, possibly needs to be running?

Mine is also a 1987

[jwmarc]

Thanks. Good to know that the voltage is applied to close off the air bypass after the car has warmed up ( start rich- closed- warm-up -voltage applied bimetal opens valve up). Not sure which relay operates it ... maybe the ECU for the lambda control.

I havent run the car in open loop to see if the car runs better ( at least once warmed up).

I tested the coil and it tests OK ( OHMS test). Also if the coil is sparking properly to allow the car to start and idle then I am not sure if the higher RPM would cause a breakdown in the coils applied voltage.

[flightlead404]

Power to the WUR and the AAR is delivered from the power supply of fuel pump 2, ie it is controlled by the fuel pump relays.

[mark houghton]

Two things in your description have me scratching my head:

"The problem is the car bogs down under load and backfires if revs are brought up to quickly. The car really runs poorly beyond idle"

"Re-installed the CDI unit and was able to get the car started, re-set timing as best I could, had to deal with some backfires"

Why did you have to re-set the timing after a simple CDI replacement? And, your comments regarding backfiring and bogging down under load or when quick throttle application leads me to think fueling, since you seem to have good spark overall. Have you checked both fuel pumps to assure that they're running? Although these cars will run with only one of the pumps working, your symptoms may be indicative of this. My car did something similar a few years ago...hard cold starting, low idle rpm and bogged badly when cold but would run ok when fully warmed up but lacking in power overall.

[lite75]

Plug wires? Plugs? Observe the motor compartment at night, might see your problem.

[T77911S]

"reset timing best I could"

was the first BIG trigger for me.

next is "no power to the WUR"

power comes from one of the FP rlys as said,. if you jumped just ONE rly and the other is not working, then you only have ONE FP working.

remove the connector from the top rear of the AFM.
turn the key on
both pumps should run.
remove each of the FP rlys one at a time just for a second to verify the other pump is running.
they will sound funny


set your timing correctly.
I don't know if you have messed with the vacuum lines to the dist. but you can check them.
with the engine running and idling and warmed up,
remove one of the vacuum lines. (I think the one on the left is retard). if the RPMs go up then that line is the retard line and it is correct.
here is a way to check the advance pot.
connect the retard line (it should have vacuum on it at idle) to the other pot. the RPM should go up. that is advancing the timing. move that line back to the retard pot,.
connect advance line.

check your timing with the advance line removed,
I believe it is 26 degrees. BTDC


verify power to the WUR.
one pin is 12v the other is ground.
try using the engine as ground, then verify the ground in the connector.
use a test light