Yet another Carrera no-start thread

[rbarton]

Hi, I have an '86 Carrera that has not run in several years. I have it back together after a (professional) top-end rebuild. While the engine was at the shop I ran all new fuel lines from the tank to the injector rails (thanks Len), had the injectors serviced by WitchHunter, and attended to a lot of 'while the engine is out' stuff. I've been keeping myself busy reading the many many threads on troubleshooting Motronic starting issues over the last couple of weeks.

I ran into something last night that I would appreciate some input on. I started checking voltage at the injector connectors and found that I have battery voltage (13 V) at BOTH wires within a single connector. I pulled the connectors off of both the #1 and #4 injectors and found the same thing on both.

This is not normal is it? If not, how can I isolate the issue to either DME or wiring harness? Or could something else be causing this?

As info, I am using the DME relay that was in the car when it last ran. I do have a new one but it was bad out of the box. I had no spark when cranking after installing it. It came back with the old relay.

Thanks for any help!!! I need it!!

[DaveMcKenz]

Someone else can chime in, but I seem to remember that the injectors have a switched ground. That's pretty common throughout the car. Both leads see 12 volts, and when one lead is switched to ground the device activates.
Dave

[jlex]

Try jumping the DME relay at the socket to make the fuel pump run (key off). Do you hear anything? After all that time, the pump may be stuck...

[rbarton]

Have already made it past the fuel pump...yes, it was locked up. New one works.

[scarceller]

You MUST unplug all 6 injectors to test for ground and voltage at a single injector harness!
All 6 are wired in parallel so you can't just unplug one.
The injector harness always has 12v on one of the pins, the other pin goes to DME pin 14&15 and these go to the injector drive transistor.

Bottom line is that measuring system voltage on both pins the way you tested is expected result.

[scarceller]

Before you go messing with DME and Relay try this simple test first:
Turn the ign key to RUN and in the engine bay be sure that the Idle Control Valve is humming and vibrating. If it is it means the DME booted up correctly and the processor is running.

Report back the result to this test and we go from here.

You will need to get a 12v LED test light, Walmart has one in the auto section for about $5.
It must be LED based light as we will use it to test speed and ref sensors as well as coil pulses in upcoming testing.

One step at a time and you'll figure it out.

[rbarton]

Good info, thanks. I'll check that ICV next and go from there..

[scarceller]

Assuming the ICV is humming with key in run then next step is to test for spark:
- Remove the hi-voltage wire from the center of the distributor cap
- Put a test spark plug onto that wire you just removed. You want to have the plug directly connected to the coil via that wire, thus eliminating the distributor for now.
- Then, with vise grips clamp the test plug to the main ground screw on intake runner for cyl #1, this is the screw with all the brown wires on it just above the distributor at that closest intake runner.

- Finally, have someone turn the key to START do you have spark at the plug?

Originally Posted by rbarton

Good info, thanks. I'll check that ICV next and go from there..

[rbarton]

Update: I'm back to working on the car again now that the holiday is passed. Hope everyone had a good one.

So, I verified that the ICV buzzes with the key on.

The car was cranking well and I smelled fuel in the exhaust, but I was seeing inconsistent spark when checking with a timing light.

I found that the rotor was broken into several pieces. I recall having difficulty getting the distributor cap seated previously, and suppose that my ham fisted efforts broke the rotor.

Happily replaced the cap and rotor, expecting the car to start. Still nothing. I am getting spark as indicated with a timing light. I have injector signals as indicated with a noid light. Fuel pressure checked good at the rail (Harbor Freight kit). As I said above, I smell fuel in the exhaust.

From the above, I figured that the car was flooded from trying to start it so much with no spark (when the rotor was busted). Pulled all spark plugs. All 6 smelled like fuel. Cleaned these with contact cleaner and blew them off with compressed air. Also blew some air into the spark plug holes to see if there was still fuel down there but got no indication of such. Let the car sit with the plugs out for several hours to let any fuel evaporate off. Reinstalled plugs and still no start. If I hold the accelerator down I do get some weak chuffs like there is some half-hearted attempt at combustion in one or more cylinders. Nothing even close to starting though.

Note that I have tried jumpering the CHT signal since I read that an open circuit there can cause excessive fuel feed. I did test the CHT sender using the Bentley procedure and it tests good.

I have tested my coil resistance using the Bentley procedure and it tests good.

Getting frustrated here. Any ideas on a next step? Is it possible that my spark is weak, and how do I check this?

Thanks for any help!!!!!!

[rbarton]

Given that I have spark, does this 100% mean that my speed and reference flywheel sensors are set correctly? They are new and they test out OK for resistance. I question if I set the gap correctly though. When the car is cranking, I barely see tiny, tiny movement in my tachometer needle. Is this normal??

If I do need to reset the gap with the engine in the car, how do I do so without having an old sensor to use?? I don't want to buy another one (and lose a few days waiting for it) if I don't have to...

Thanks

[jlex]

If you removed just the sensors, there's no need to adjust the gap. If you removed the sensor holder along with the sensors (say, if they were stuck) only then would you have to worry about the gap.

[rbarton]

Yes, bracket was loose. Engine was apart for top end rebuild.

[zippy_gg]

While the engine was out, was the distributor removed?
If so, was it re-installed in the correct position?

[rbarton]

I carried the engine in to a well respected local Porsche specialist. I have little doubt that the engine not starting is due to something I did, not him.☺

[jlex]

If the actual bracket holding the sensors was removed, the clearance between the sensors and the flywheel must be re-established. Hopefully, someone will chime in with the clearance. Those who have been through it located a properly sized, correct thickness washer which they glued to an old sensor, then set the bracket with the old sensor/washer touching the flywheel. Once removed, the new sensor can be installed with the correct gap. Sometimes the washer needs to be sanded down to the correct thickness. Do a search for a more thorough explanation.

[CCM911]

Did you replace the fuel filter?

[ischmitz]

If you have consistent spark and fuel the sensor are NOT your issue. I would start looking at the distributor position as others said. Also, are the spark plug leads in the right position.

I get it that you first look for mistakes you made. However, as the top end was apart the leads were off the distributor. So let's not assume but check:

Engine needs spark (at the right time), fuel, air, and compression (at the right time). Then it will fire. Check for each.

Good luck,
Ingo

[scarceller]

Use a small soft metal washer and sand it down to 0.8mm thickness. Then hot glue it to the end of the lower sensor (Speed Sensor), loosen both bracket bolts, reinstall the sensor into the bracket and let the bracket move toward the flywheel till the glued on washer contacts the flywheel. Hold the bracket in this contact position and tighten the bracket bolts. Remove the sensor and pry the washer off the end, reinstall the sensor.

Using hot glue makes it easy to remove the washer from the new sensor. I have an old sensor with a washer epoxied to it but you will need to do this with the new sensor since you don't have an old one.

To test for spark strength I suggest you put a test plug directly onto the ignition wire that goes from the coil to the dizzy cap. Unplug that wire from center of cap and put plug directly to that wire and then ground the test plug to main ground screw on intake runner #1. While cranking you should see nice bright white spark, if the spark is weak it will be more orange color than bright white.

[scarceller]

I agree, if you are unsure about dizzy install you need to take it out put engine at TDC #1 and then be certain you get the dizzy back in so that the rotor is dead on dizzy mark for #1. And make sure the plug 1 wire is in the correct post in the cap and that the rest of the firing order is correct. Or just put the engine at TDC #1 and double check the rotor is pointing at the #1 mark on the dizzy housing.

I also suggest a compression test to be sure you don't have yet another possible issue.

Originally Posted by ischmitz

If you have consistent spark and fuel the sensor are NOT your issue. I would start looking at the distributor position as others said. Also, are the spark plug leads in the right position.

I get it that you first look for mistakes you made. However, as the top end was apart the leads were off the distributor. So let's not assume but check:

Engine needs spark (at the right time), fuel, air, and compression (at the right time). Then it will fire. Check for each.

Good luck,
Ingo

[rbarton]

Much appreciated. So here is where I am currently. Last night (before I read some of these replies) I took a good look at the flywheel sensors. I pulled the reference sensor out and found that the end of it was boogered up as if it had contacted the sensor pin on the flywheel. I wanted to check the speed sensor as well but was unable to get it to budge with the engine installed. Since at this point I was fairly sure that the gap was NOT set correctly to begin with (by me), I went ahead and dropped the engine. I'm getting pretty good at this Right now I'm waiting for new sensors to arrive. Will CAREFULLY set the gap, get everything back together, and reinstall the engine. Probably be a week or so.

While the engine is out and after reading some of your replies, I took a look at the distributor position. Note that I had checked and triple-checked that my plug wires were correct, and did so again last night. So here is my rotor position at what I believe is TDC :





Timing marks with rotor as above:





The rotor is well past the mark on the distributor housing...This isn't right, is it???? How do I correct, just pull the distributor and set it back in with the rotor centered at the housing mark??

Thanks again!!