william_b_noble

maybe it isn't weak spark? this is where an ignition scope could be handy (I happen to have one but you aren't very close) - I also had weird problems on NA and 16V cars with the air flow sensor, so that could be worth checking. it is also worth making sure you have a real clean ground connection from the block to the chassis - the connection above the flywheel where these grounds attach frequently gets corroded, with weird effects.

xsboost90

i would check the air meter- if the slider under the black cover is worn, it will give you hiccups, and if the door itself is sticking it will do the non start issue as its fine at idle but when you pick up the rpm the door will not open and it leans out. Make sure the door swings and give it a shot of wd40 or something at the hinges.

Austin87

Hi "specsalot"....I have not done close to the work on my 87 924S as you have done on your turbo, but if you read my Feb 2nd post I copied below I am pretty sure I have the same problem as you do ( or did) . If you ever do find a fix please PM me or post it here. Thanks, Austin


......
Long story but have to go step by step. I have an 87 924S - purchased in September from a forum member Robert Hughes of Orlando who is now moved to Iowa. The car was his wife's DD for 7 years and he did tell me he was a Porsche Technician and always meticulously maintained the car for her.

Problem I have is since I have the car, there has been a problem with the car cranking but not starting about once a week. When running the car always ran very smoothly. I remembered Robert the PO telling me something about if the car gives me a problem no starting to clean the grounds or just wiggle the Ref sensor wires around and the car will start up. He said that eventually it will probably be a good idea to install new ref sensor wires.

This went on for the first 3 months or so and I figure soon I have to replace the 2 reference sensors. Then in about December of month 4, this would happen more frequently to about 3 times per week. And maybe have to give more than 1 wiggle of the wires to get it to start. But still after 2 or 3 tries of wiggling the ref sensor wire the car would start up.

When driving the 924S I put on about 5,000 miles and the car when it is running always ran very well. Idling - accelerating - shutting off and coming back on . Unless this issue would come up but it always ran smoothly.

Then about 4 weeks ago one night after starting up and driving like 50 yards the car actually stalled out on me for the first time, and didn't start back up. I eventually got it to start up after like 10 minutes of waiting , but it stalled out quickly. I put in the new DME relay I had just for good measure but it didn't fix the problem. I eventually drove it home like 2 hours later about 3 blocks on it's own power.

Since then I had the 924S towed to Mike Goeke at German Performance Inc. in Ft Lauderdale who I was referred to by a member here or on Pelican. Mike Goeke tells me he is a 45 year Porsche factory trained technician and he has a garage full of Porsche's which seem to back up he knows his way around them very well. On the first try with the car Mike tells me he can diagnose the problem only if the car is not starting & he did have that chance after I had AAA tow it to him, about 4 weeks ago. I told him I think maybe I need to clean or change the reference sensors but he said this is not possible to be the problem. I am not an auto mechanic but he is so I let that go even though it is against what I was told could likely be needed by Robert Hughes.

What Mike did was swap out my air flow meter for one he had in his garage and told me the problem is fixed. It "started up 20 times for him, plus it now ran smoother and sounded alot better". Then the night I was going to pick it up he had a guy move it out and it didn't start. They now cleaned the ref sensor cable grounds and switched them around and it was now starting w/o stalling out.

* He also tightened my loose Water pump belt and installed a low radiator sensor switch which he found I needed because the car was running hot and the radiator was cool so my pump wasn't turning . I was very grateful he found this out. So I picked it up . ( $500.) Drove it home 30 miles highway and street with no problem. Then I went out to start it 10 mins later and it did not start up again. Tried the same things with the wires and no luck.

Last Friday afternoon AAA Towed it back to German Performance this time with 2 new reference sensor wires for him to install. Today I picked it up . It started for him fine he said and for me 2 times so I drove it home ( again). Back to move the car 30 minutes later and same problem again. Car won't start. Wait a few minutes and it starts and stalls out. Wont start - called Mike Goeke and the call did not go well. He said he needs the car when it is not stating in order to diagnose the problem correctly not after a new air flow meter and new sensors. I tried telling him that is where we started out but he was not happy to hear that. A minute later on my 3rd try to explain this point , he hung up on me. Here is where I am now.

Anyone have any suggestions on what this could be or where to go with it. To me it seems like it would be a lack of getting fuel issue. I have had it with the car and being an automatic even though I put time and $$ into this and it is alot of fun to drive I want it fixed and gone. First fixed .

Thanks, Austin ( West Boca Raton , Fl )

specsalot

Thanks all - I'm working step by step. Progress is slow as I do this in my spare time. Parts are on order. I checked the TPS and found that the contact closure in the TPS is bad. Parts on order (FCP Euro $123). Working through the process awaiting other parts as well.



The microswitch is located in the lower left corner of the switch above. Note that the micro switch "tit" does not project through the switch housing. The switch is open and cannot be actuated with mechanical probe. So the DME would be thinking this car was on partial throttle operation even while at idle. This explains the heavy fuel flow. I didn't check the rheostat sections because without the contact closure, this device won't deliver the goods.

Thanks for the feed back. I'm going to keep reporting out my findings as I move along.

specsalot

My brother has a friend who may be nearby with a sophisticated SCOPE / analyzer (Snap on from 95 costing upward of $5000). If I can't solve this we'll try to run this guy down for support.

Grounds and ground cable are going to be revisited (again). I've pulled all the ginger bread off the engine and will be pulling the full DME harness (again) this time for full point to point verification.

New ground cable, new B+ cable, new alternator / starter cable [all Porsche OEM] are on order. All ground connections were cleaned when I did harness work. But the ground ring terminals were kind of iffy. These will be cut back with new ground terminals installed on the DME harness when I have it out.

The was another "grand baby" weekend. So I hope to put a major dent in diagnostics this week. I'm off work until Thursday night While I'm this far into it, going to do belts, also install a new cap and rotor. There is some tracking in the cap. Good time to change these components although what is there has a few miles left (will be kept as legitimate UBG spares).

specsalot

Austin - I saw your post and realized you've got a very similar problem. I can appreciate your frustration. The issue with my car was "sudden" on-set. Different from the usual sensor "wire wiggle" drill that occasionally plagued the vehicle. As I've drilled into this issue, I'm more amazed the car was running at all.

xsboost90 - I will lube up the door on the AFM. It doesn't feel sticky. it will measure the AFM resistance over travel range to see if I've got some bad spots. The car had very little drivability issues up until this point, so I think my AFM is probably intact like all of the rest of the "vintage" parts of the car. A while back the fuel economy seemed to notch down. It was also about the time that the idle seemed to drift around a bit more then usual. [This is probably when the TPS microswitch failed]. The TPS problem should not make the car a non-starter.

william_b_noble - Grounds are first on the list at this point. They were cleaned, but the ring terminals were a bit "iffy" and as far as I'm concerned a bit flimsy for the task. They went back down on my first review with new "star" washers. There is plenty of room to cut back the leads, there may be some broken strands near the connection. Now that I've gotten a better understanding of the role that these grounds play in the operation of engine electronics, I think they deserve a more skeptical review. I have seen poor grounds on other vehicles deliver some very strange results. Electricity behaves very logically (path of least resistance, kirchoff's laws, etc), but electrical problems can produce strange symptoms.

Thanks to everyone for taking the time to read and post.

specsalot

Todays Progress - I was hoping to find loose grounds. No such luck.

Ring terminal lugs had been soldered to the cable. The engine ground had a few broken strands, so I've cut it back and will be putting a new lug on it.

I pulled the DME harness and have started going point to point through it. So far no problems found.

I also dismantled the Throttlebody. Seals were nonexistent and the TB was pretty gummed up. I cleaned it up (Gunk dip / brush) and resealed it. Bruce (Arnnworks Specialty Tools) puts together a decent yet reasonably priced kit with good instructions. It takes a bit of patience to get the new seals properly installed.


Still waiting for parts to arrive.

specsalot

I cut back both ground lugs and crimped / soldered new ground lugs in place. I will be doing a point to point inspection of the DME harness based on the following notes from the shop manual / wiring diagrams for an 88 944 Turbo:

https://www.dropbox.com/s/75ibb6xjvx...Pin%20Outs.pdf

New ground lugs in place:

specsalot

Arriving tomorrow - distributor refresh



Arriving Friday - TPS



Arriving Saturday - Cables / Misc

specsalot

Going point to point in the harness - Discovered that the LR-944-Ref harness repair kit was miss wired. On the DME side, the kit wires are carefully marked and color coded. The instructions for the kit are well written. A no brainer to install.

DME Pin 27 is "black" (and numbered) - According to the shop manual schematic this should be RPM Sensor plug pin 1
DME Pin 8 is "clear" (and numbered) - According to the shop manual schematic this should be RPM Sensor plug pin 2

Point to point exam found that the RPM Sensor plug wires for pins 2 and 1 were swapped. Rather than dismantle the RPM Sensor plug I swapped the connections within the DME plug.

Test Point 4 (Reference Mark Sensor) instructions caution that the wave form form must begin with a + slope. Reference Mark Sensor pin outs have been confirmed to be correct between the sensor plug and the DME plug. In contrast to this Test Point 3 (RPM Sensor) instructions do not have the any caution about the initial slope of the output wave form.

The open question is whether a 180 DEG shift in output from the Speed Reference sensor would make a difference to operation? My limited understanding is that two inputs are combined on the digital side of the DME unit and processed digitally. Perhaps someone with deep knowledge of the DME circuit can weigh in on this question?

UPDATE - Completed the full DME/KLR harness check out. No other wiring defects. Harness will not go back in the until I have the battery cables installed (arriving on Saturday).

specsalot

New cables arrived today. I realize there is only a small probability that this is an issue, but at least now it will be off the table. Old cables were a bit ratty and showed internal corrosion. New timing belt / retention BS belts today - Then let the reassembly begin. Distributor parts arrived. TPS delivery was pushed back until Monday most likely due to weather issues.

specsalot

Update - (this is becoming a project)
New Battery Cables Installed
New Timing Belt Installed; Both Belts tensioned
DME Harness Reinstalled
Cleaned and Inspected J-Boot - Found some nice cracks - Parts on order
Tested AFM - found a nice flat spot / open circuit at partial opening - rebuilt exchange AFM enroute

specsalot

Sorry about slow updates - Found another cracked up hose (molded elbow on top of oil separator). Parts on order.

specsalot

Sorry - Slow Replies - spent a couple hours on the car today - No start - NO SPARK. The engine does crank over well. The new cables made a difference. Car had "weak spark" (no start) after putting the rebuilt DME in back in Jan. Now it has NO SPARK. Fuel injection is delivering fuel. I'm waiting for a call back from Specialized ECU for additional feedback guidance.

Operating the ignition coil straight off the battery (intermittent energize primary, grounded spark plug in secondary) doesn't produce a lot of spark.

With everything hooked up I tried to measure current draw through the coil primary today using a Fluke 337 clamp meter. Also separately using a Fluke multimeter in series. Both results showed 0 amps through the coil primary circuit. These symptoms point back at the DME analog circuits which operate the coil.

specsalot

Update - Had a phone conversation with Specialized ECU. Late today I shipped off both the DME and KLR for combined bench testing. My bet is something let go in the DME. I'm hoping to hear something before the weekend of computer status.