Engine miss, tach drop, now will not start

[99hdtop]

I went for a short drive this morning, while cruising in 4th gear at about 3000 rpm I had a quick engine miss. It happened again a few minutes later and I noticed the tach drop before the last engine miss. I was only a mile from the house so I came home. Tried to start the car 30 minutes later to check voltage at battery and it will not start. Cranks over good but no start. What now?

[ossiblue]

Check for spark.

[timmy2]

Check for fuel too!

[99hdtop]

I did a test for spark and when my wife hit the key it started. I killed the motor, re-installed the spark plug wire, started the motor again and it ran for about five seconds and died. It would not restart. What is up with that? All the ground wires are good as far as I can tell. The ground at the neg cable for the battery is good, ground at fuse panel (below strut tower) is good. Ground on intake is good. The only one I have not checked is behind the fuel filter. Chassis to trans is good also.

[al lkosmal]

If this is happening to the 85 Carrera listed in your garage......swap out the DME relay. 1st thing to check with the 3.2. Keep a spare handy.

regards,
al

PS: search the Pelican tech forum using "DME" as the search word and you'll find all the info related to no-starts relatedto the DME relay.

[99hdtop]

Thanks al, I appreciate your help.

[Chuck.H]

If you can get it in the condition, check the reference and speed sensors for resistance (they should not be 0 ohms). They are one of the few components that can cause the tach to drop suddenly. The other is a failed DME relay so check that first. After those, you may want to check the DME itself for cracked solder joints.

Chuck.H
'89 TurboLookTarga, 363k miles

[theiceman]

although DME relay is high fail swap that but stop there if it doesnt fix it .. trying to swap parts without diagnosing can be long and painfull to the pocket book ..

What you should have done was after it died, go check for spark .. as the problem is intermitent .. if it does that again check for spark right after it dies and is in a no start condition.

Spark is the easiest thing to check , report back what you find .. we wont make any parts swapping suggestions until you come back with this result.

[99hdtop]

I did change out the DME relay today after work. It did not fix my problem. It is in a no start condition right now. Yesterday it would start for about 3 seconds and then die, today after changing the relay it would not start at all. Tomorrow I will check for fire at the plugs again. Thank You for the help, I appreciate it very much.

[99hdtop]

I checked for spark at one of the plugs and now I have none. I checked the ohms at the coil per Bentley and it checks ok. I guess now I need to check the speed and position sensors? I was really kind of hoping it was the coil, oh well! Any suggestions theiceman?

[Chuck.H]

Sorry to sound repetitive -- did you check the resistance of the speed and reference sensors?

Chuck.H
'89 TurboLookTarga, 363k miles

[99hdtop]

That is my next step. But it will be a day or three before I can do it. Thanks! Need to check the voltage at the coil also.

[99hdtop]

Resistance at speed and ref sensors is 1,051ohms. well within range. While I was trying to get ref sensor loose all of the black rubber that covers the wires crumbled to the floor. I hate to leave it that way, so I think I will purchase new speed and ref sensors from our host. BMW part number 12 14 1 708 618 will work and is half the price from what I have read here on the forum. Why are the Porsche sensors so much more $$$? The grommet that separates the engine bay and holds the wires is a bear to get out! I have not been able to get it out yet. My distributor cap and rotor needs replaced also. The shaft in the distributor is rusted also, Can I use a wire brush and some WD-40 to clean that without worry? I have never seen a dist shaft with rust on it before, they are usually nice and clean. Thanks for any help.

[Tippy]

Stick a screwdriver in the holes of the grommet and twist until it pops out.

[steely]

I think you'll have good results with replacing the speed & reference sensors.
Given your symptoms and the state of the crumbling insulation, this cannot be a bad idea.
They're close to 30 years old already, and at the least they needed replacing.
Start to prep the area by jacking her up, and removing the drivers rear wheel - and removing the grommet to the firewall.

Clean the firewall as best you can (blindly) with a wet paper towel - it will help the new one go on. If you have silicone or water based lube, that will help with the installation - show it who is boss.

Prep the sensors nuts by spraying them with wd40 or kroil or PB blaster now. slow but sure.
The bmw parts are half the price, same Bosch quality, and a bit longer to boot.

Let us know.

[99hdtop]

I changed the reference and speed sensors, the coil and distributor cap, rotor bug and plugs. I also changed the DME relay. I went for a spin to check out my work, and wring this little cars neck a bit. Tach fell three times and a miss with each drop. Got the car home and it dies in my driveway and then restarts. It dies again when in the garage. DME time I guess!

[ischmitz]

I think you got to the right conclusion. Once the speed and reference sensors are replaced and the DME relay is cleared I think it is time to focus on the DME. If you need it checked out drop me a PM. Given that the tach falls it pretty much means no spark as opposed to a fuel starvation issue.

Cheers,
Ingo