spacedoc

Hi, all... new member here. I just bought an '86 N/A 944 project car and I have some speed/reference sensor questions (shocking, right?)

The engine is in good shape, but it will sometimes not start when it's hot. I don't think it's the DME relay (recently swapped). The PO told me that he thought it was the speed or reference sensors, and recommended connector jiggling when it happens. It's never not started when cold for me, and even when it won't start when hot, after a few minutes of connector jiggling it eventually will.

I do think it's the sensors, since I don't get tach bounce when it won't start, and whenever I finally do see tach bounce on an attempt it starts right up. That said, I'm not sure it's the connectors. The connector harness was replaced with what I now know is the LR replacement harness, and the sensors look relatively new. I've used deoxit on both harness connectors, with no improvement.

That leaves gapping. I've removed the sensors from the bracket (both came out easily and after wiping off some oil look brand new) and have learned two things: one, I am definitely going to have to remove the intake to adjust the bracket. My fat hands are just not going to cut it with the limited space back there. And two, there was no "figure 8" washer.

In searching multiple forums I've seen: no reference to a figure 8 washer, statements that it must be installed on the speed sensor, statements that 951s require it, but no explicit mention of N/As needing it, and a note that there are different brackets that require different thickness washers.

So at this point, I'd like to know: do I need a "figure 8" washer on the speed sensor, and if so what thickness? If I'm going to remove the intake to regap the sensors, I would like to have the greatest chance of it actually working... I took some photos of the bracket, and of the sensor ( http://imgur.com/a/rjIvN ). The sensor does not look like it has any marks that would indicate that a washer was there at one point or not, but it seems like maybe there's a faint outline on the bracket. How loose is that washer on the sensor? Is there a chance it could have fallen off when I removed it?

If anyone has any suggestions, I would greatly appreciate them! Thanks!

mytrplseven

Ok, I've been down this road recently on a barn find 951 and here's the picture of what I found. After looking at the parts list, I found there's two shims listed. The thicker one is for the 951 and the thinner one is for a 944 N/A but not sure what years. You have to install the proper one and then adjust the clearance on the sensor according to Clarks Garage. I found that a large, round electric connector (spade lug) was not only the proper diameter to glue to the bottom of the ref sensor, but also the 8mm thickness. I got it at Home Depot.

Using the AutoAtlanta parts breakdown for 85.5 and later, part number 94410133500 is a .3mm shim for the N/A and 95110132500 is a 2.0mm shim for the 951. Those parts are cheap (less than $2). I hope this helps.

My picture is because the speed sensor was replaced without the shim and no gapping was done. It didn't last long. The PO did this recently.

spacedoc

When I pulled both sensors they both looked brand new. Neither were marked or chewed up.

odonnell

Smart thing to do would be to use a 0.8mm thick shim (people use washers and stuff glued to the sensor) to measure the gap on the speed sensor, as it is.

You also need to find out if the washer was factory on your motor...maybe someone here can tell you. If it was, and you leave it out and proceed to gap the sensor, the reference sensor will be too low and may clash with the set screw on the flywheel.

CyCloNe!

I thought u dont have to adjust them unless you unbolt the bracket?

spacedoc

Theoretically, no... But I'm not sure what the previous owner did. I know that the clutch was replaced about 4 years ago, so they must have been regapped then... The question is, did they do it correctly?

CyCloNe!

Ya if the car hasn't run since purchase then it wouldn't hurt. If it was running fine before hand then I wouldn't mess with the gap.

spacedoc

It does run fine when it starts, but it won't start sometimes when hot, and when it doesn't start there's no tach bounce. That's why I think perhaps the gap is wrong. If there's supposed to be a washer/shim and there wasn't one, then the speed sensor could be gapped correctly, but the ref sensor wouldn't be.

odonnell

VR sensors aren't really temperature sensitive...they're very robust and can withstand a huge temperature range. You said they're recent sensors... IMHO it's far more likely that your issue is elsewhere. There are a lot of threads where people have had issues with hot starts. Check out your FPR, and your DME temp sensor.

spacedoc

odonnell, thanks for the suggestions. Before I go to the trouble to take the intake off, I'll reinstall the sensors and then check the FPR and DME temp sensor... can't hurt, right? I've been focused on the speed and ref sensors since I don't get tach bounce when the car doesn't start.

odonnell

Missed that part when I read the post. Still, I'd check out other areas too... DME relay (I know it was swapped but there a lot of bad quality aftermarket relays out there that are bad even new), the DME itself, and the wiring where the patch harness connects to the DME harness for the speed sensor. It's possible it was done sketchy.

FRporscheman

I think a faulty DME relay can also prevent tach bounce, so it might be that.

spacedoc

Update: I checked the gaps with a wooden dowel and they both seemed right, which would imply that a washer/shim is not needed.

I read on Clark's that occasionally if there are metal finings gathered on the tip of the sensor it can interfere with a reading. When I took the two sensors out of their brackets, there was a film of oil on both of them, which cleaned right off. The clutch area looks dry through the inspection hole, but there is some oil on the outside of the block near the brackets (need to track down that leak...), and I think it wicked its way down from the top.

I figure maybe there were some metal particles in the oil, so I went ahead and reinstalled both sensors. I went for two test drives to warm up the engine, and after each the engine started right up. It's early... but hopefully this was the problem.

Thanks to everyone for their suggestions. Now the next project: I just noticed a delaminated hatch that was likely made worse due to new struts and me slamming the hatch multiple times to adjust the pin seats. Yay.