Hard/No Start After Refernce Sensor Project
 

I have been working on replacing my reference sensors because of a no start issue, tach would not bounce, sensors tested bad.. It seemed like it took forever. But, I finally broke down and removed the manifold and the AOS, time for new seals anyway, much easier to get access.

I got everything back together, it would start, but ran bad, hard to keep running. I did an air test and found a few leaks, removed the manifold and fixed the hoses and TB leak. Now I get everything back together and it wont start at all.

Its getting crazy... I checked all of the the temp sensors per Clark's Garage. I checked all of my hoses. My tach bounces. It "wants to start" but just wont go...

So i decided to do the DME relay test, put a jumper in the socket, I could hear the fuel pump, but when I turned it over I did not get that "wants to start" like I did with the relay installed.

Does the jumper method provide more fuel on start-up than the DME start-up? I am not sure what means if it does, but might lead to the resolution.

Any ideas would be appreciated.

Did you verify the new sensors were gapped properly and plugged into the right plugs? If so, next best bet is DME or harness from sensors to DME.

I used a washer with the old sensor to gap them.. The connectors look good as new.. I will trace the harness and double check..

One thing I did today was do the Clark's Garage test on the AFM. It passed with flying colors.

While I had the filter cover off, I looked opened the AFM door and tried to start the car. Wham, started on the first turnover, of course it was at 3-4k RPM. So I shut it down and tried again with the door only open a little bit, no start.

So , I definitely have an A/F Ratio issue, so what's causing it? Most items on the fuel system are only 3 years old, did something gum up on me while it was sitting?

When we changed an engine on my race car, it would start after a long crank but run like it was out of time and then die. The tach would show a slight bounce. After several days of checking everything someone suggested to switch the reference sensors and see what would happen. It fired right up and ran great. I have asked a number of experienced 944 Spec builders and racers and no one had ever heard of this happening. If it happened once it could happen again.

One of the Porsche factory motorsport mechanics once told us at a race, if there is a starting or running problem, look at what you worked on last. The majority of the time this is where the problem is located. This has turned out to be true most of the time.

Good advice, I will retrace my path and swap the sensors

You just need to swap where the connectors plug in. There should be labels on the harness side, one was missing when I did my clutch, but I had the other so I knew where to put them.

I tried switching the sensor connectors and wasn't able to get the car to start. I am going to re-gap when I get some time to rule out the sensors. Maybe they moved when I was tightening the bracket. Thanks

BTW, when I step on the gas the car starts and stalls under 2k rpm..

I just pulled the new sensors, it looks lit one of them was rubbing on something or got swiped. Hopefully I can resuse it. I will re-gap and see what happens

I had some time last night to re-gap the sensors and still get a no start.

For some reason, i can't help but think about one of the sensors had a rub mark on it. Also, my clutch pedal is on the floor. Maybe related?

Time to go back to the basics, spark, fuel, air...

Air is tight... Did pressure test, found a few minor issues, resolved them
Fuel is good (too good)! All fuel components are less than two years old.
Spark - Replace plugs because they were black. S

So not enough spark or too much fuel. Car sat for a while for the sensor repair (they got stuck)..could be a factor as well..

It sure sounds like an AFM problem - except that it passed the test.

More than once I've forgotten to plug the AFM back in after I've had things apart and the engine will sometimes run but poorly.

The mark on the sensor would indicate that either it was installed too far in or there's a problem with the plug on the flywheel? Maybe pull the starter and take a closer look?

You pulled the manifold so there's that gasket and the vacuum lines to look at.

I don't suspect the fuel system but in a case like this I would measure the fuel pressure at the rail cap.

Make sure you let us know when you get this whipped.

GL

http://www.gouptoday.info/avatar1.jpgwhen I step on the gas the car starts and stalls under 2k rpm.

Used the washer technique on the wrong sensor?

you have a big air leak? try to see the j-boot,maybe broken under it.

the conection of AFM is not ok? On my car someone rotate a few times the cable,cable broke and made contact with onother one,must rebuild it

the conection of throttle body-the same of AFM

the conection of water temp.sensor-same as AFM-hapened to me...

look your air filter,maybe blocked?

when you rebuild the reference sensor hausing maybe in some way you broke the reference bolt:try to give a full cyrkle and find the bolt for the first sensor,it must be out of the flywheel about 3 or 5 mm,i don't remember but is easy to find in manuals.

maybe you destroy the clutch(if is rubber one) and you have piece of rubber on the flywheel and sensor can't works good?

ultimate resurse:look carefull the flywheel,maybe do an oval cyrckle or something broken?

good luck

I pulled the starter today, looked through the opening, turned the engine by hand, all looked clean.

One thing I did notice in searching the internet was a figure 8 washer used on the speed sensor. My sensor was seized to the bracket so i did not know about this washer. It's not on a parts diagram anywhere. Although the speed sensor is gapped correctly, This would make the reference sensor 2mm out of the required gap. The spec for a 85/1 is 8mm +/- .05.

Back to square one!

The correct gap for the Speed Sensor is 0.8mm (Between the speed sensor and the ring gear) - not eight whole mm's.

I'm sure it was just a typo there huh.

Thanks, Good catch!

I spent some time on the 944 this weekend to check the gap on my sensors. I found them to be per the spec. The spacer in only needed on the speed sensor on 85/2+ cars. Mine is a 85/1.

I spent some time going through my receipts folder and it dawned on me that the gas is two years old! So i put some Kreen in the tank, it started, but ran rough, really rough. Although the Kreen did not solve the problem, it gave the gas enough life to want to start the car. I am thinking water in the gas.

That Cat was hot, meaning too much gas making its way through the system. Fuel pressure was perfect, leak down test did show no leakage, I tested the spark with my timing light, seemed fine. I pulled the DME and did not see any bad solder joints. I am guessing weak gas not burning off in the cylinders. The only other thing I can think of is timing.

Its only Monday and already I have my weekend project planned..draining the gas tank. Between my boats and my 993 that I just sold, and now the 944.. Ethanol is not my friend!

Def drain the gas and don't forget the fuel filter. I'm sure it's contaminated too!

Since most people never report back on the status of their problem.. Well I wish I could say its been fixed, but that latest idea was to drain the fuel, and that really did not help. Back to the beginning again..

So I think the car is running rich based on the plugs and the Cat gets too hot, but I am getting backfire though the intake which I have read is caused by a lean mixture or bad timing.. This started as a no start & AOS seal fix. This is what I have checked

1. Replaced Ref & Speed Sensors, Gapped, Regapped, Regapped again, checked for ohms at computer plug.
2. Check Temp Sensor, Ohm reading within spec.
3. Checked for spark, passed
4. Fuel pressure test. passed
5. Compression test, passed
6. Checked AFM with Ohm meter, seemed OK
7. Replaced Gas in tank, no changes
8. Check Cap and Rotor, look good as new
9. Checked injector signals with noid light
10. Air pressure test intakes, fixed all leaks
11. Opened computer, no cold solder joints
12. New plugs, but they turned dark fast, fouled


I have a feeling I am overlooking something simple, although I am getting frustrated, Failure is not and option!

Backfire through the intake? Plug wires in the right places? Rotor properly secured? Speed/ref wires plugged into the right sensors? Did you gap the correct sensor (speed, NOT ref)?

http://i124.photobucket.com/albums/p...nsta/wires.jpg

Thanks Rasta, I will check the wires again. Just to make sure, the cylinders start #1 up by the front of the engine, and are in order of 1, 2 ,3, 4 towards the firewall?

Also I swapped the ref & speed sensor wires and got a no start and no tach bounce

Yep, #1 is at the front.

The wires are in the correct order and yes I did use the speed sensor to set the gap.. Thanks!

Hello back again.. So I keep thinking the sensors are the pint of the problem. So I pulled the connectors again and played with the grounds. Both grounds are good. So i thought I would check the pins on the connecter side that goes to the DME.

I noticed that on the speed sensor, there is some type of resistance on the other two pins, but on the reference sensor, only one pin has resistance, the two others are to ground.

I pulled DME connecter, and there was no continuity between the wires. So the ground on he center pin of the Ref sensor must be in the DME. Is that normal?

False call. I just found a DME diagram on Clark's, it does go to ground!

Hi fsr,

Sorry you're having so much trouble. Keep at it: you will find that problem.

Because this thread has become a bit of a saga, I'm not sure I understand the symptoms correctly. Are you saying sometimes it won't start at all, and sometimes it will but runs poorly?

Meaning it runs well enough to drive, but poorly? Or just starts and stops right away?

I'm presuming from the fouled plugs you've got it running for a while. Is that right?

This may be a complete red herring, but did you check the electrical connectors to the fuel injectors? If one of more is bad you could get a rough start-up sometimes, I think, and other times maybe nothing at all (no circuit).

I had an incident like that recently, and the two sets of symptoms (sometimes no start, sometimes running rough) had me foxed. Turned out to be simply a badly-repaired connector.

Good luck.

Thanks for your words of encouragement. I bought this car for $ 1500 and felt that it was a safe investment to learn more about cars and take my tinkering to the next level.. Although frustration has kicked in, its been a great learning experience. Everybody on this board really loves 944's

As far as the runs rough, it wont really run at all under 1500 rpm, its a no drive situation. If I do get it started I need to give it gas to above 1500 rpm to stay running. It does stay running, but not like it should. Plus the Cat gets really hot. I did the fuel test per Clark's and a noid light test

I am still leaning towards the sensor, and or timing, or DME related. Did the TDC check.. I am going to the "pick a part" on Saturday, going to look for a used DME, AFM and anything else I can get my hands on. All of the fuel system is newer, so the high ticket new parts is what I am in search of. Something is wrong that is not obvious, at least to me. Although It passes every test I could find on the web, there is nothing like having spares for troubleshooting. This yard is cheap for parts, so worst case I can get rid of everything on Ebay and not loose money.

Also, I need to backtrack my steps. I started with the sensors and bracket, pulled the intake to make it easier (did a pressure test to check my work), re-did the AOS seals. Could the AOS or how I reinstalled it be dong this? I started this project last fall, could a critter crawled in the exhaust? Maybe something else went bad when it was sitting for so long. Maybe one of my new sensors is flakey?

Many years ago, as a prank, we used to stuff a potato into exhaust pipes so the car would not start - they will not start unless the pressure blows the object out of the pipe. We soon stopped that when a friend ran up a considerable garage bill getting it figured out, and was mad as - well pretty mad.

I am getting close. Wow learned a ton about sensors on this project...

I read on a 911 board that the reference sensor is only used to start the car. Once the DME gets its signal, it will take over the timing. So, i used my spare sensor plugged into the reference sensor harness. tapped a screwdriver on the sensor and had someone turn it over. Once it started I stopped the tapping. The car started and ran OK, not great, but remember my pugs are now fouled and I need to adjust my Air/Fuel screw on throttle body because I rebuilt it. I did get it to idle at 1100 rpm, that's a first.

I figured out a trick to test the reference sensor, with the ignition on (not started), and with the sensor plugged in and removed from the bracket, you should see the FPR and lines jump a little when you tap the sensor face with a piece of metal. The tach bounce seems to be the best method to test the speed sensor.

I think i might have damaged the flywheel stud when I first (1st out of 3 attempts) gap'd the sensor bracket. I still sticks up off the flywheel, but probably not 5mm, I need to figure this out. Or maybe my new sensor is trashed.

So re-gap or re-sensor, new plugs, adjust air flow.. hopefully this will work. It only took 29 post!

If you are starting but not idling or you are running rough.

Look for a vacuum leak.

Look for a hose not connected into the throttle body area, some of them are underneath.

This bites us all the time on our race cars.

m

Hey FSR,
I've been following your posts and I've had the exact same problems for over a year now... So fkn frustrating! I'm trying to keep the faith too. Yesterday I was tinkering.. I changed all of the vacuum lines with those nice silicon ones. I made a pvc cap with an air fitting on it and did an air test. I put a brand new intake snorkel and squeezed it back and forth to try to see where the air was going. I heard a clicking sound so I got my buddy to come over and squeeze while I crawled under the car to see where the sound was coming from. It is coming from a cap at the rear of the balance shaft. It popped in and out as my buddy squeezed. Does anybody here know what that cap is? I'm wondering if that is where my vacuum leak is? It looks like some oil has been slightly leaking for some time. I guess that I'll have to take my entire balance shaft apart...
Anyway where are you located? I have a spare rebuilt dme that if you were close I could lend you.
Any help would be appreciated... Good luck

That leak seems very common. I saw a post that said put some RTV or gasket sealer around it with you finger. Also, your testing it under pressure, not vacuum which it usually sees with a normal engine running.

One thing I did learn is that the DME will retard the engine if its getting a false, no or erratic reading from one of the sensors it monitors. Two signs of a this are running rich and low vacuum. So if you pass the air pressure test, fuel pressure test, spark test and clogged exhaust test, go pack to the DME sensors (TPS, Temp, AFM, Ref, Speed). Also, the spec for the sensor gap on pre 85/1 cars has a smaller tolerance than the 85/2+ cars.

Good Luck!

Thanks fsr,
I was thinking about gobbing some silicone around it after cleaning the area...And good point.. the disc will be sucking in. So I'm not aware of any exhaust test... Maybe something crawled in there..? Hehehe! What is it? I looked on ClarksGarage and didn't find anything on it...
Also Mine is a 1986 and I don't remember seeing any washer/ spacer on the speed sensor... maybe it got lost. Do you know how thick it is supposed to be?

The Exhaust test... I found this on U-Tube. I used my vacuum/low pressure gauge, connected to the exhaust test port, started the car, My reading was less than 1 psi, bounced a little when I revved the engine, but not much.

Also, I thought the same thing about the washer on the speed sensor. Figured I dropped it pulling the sensors. Then I looked in the parts look-up, it only show the washer for 87+ cars

Hey Aussie,

This thread, currently on the front page, may help in deciphering the diagrams:

http://forums.pelicanparts.com/porsche-924-944-968-technical-forum/635898-quick-primer-reading-porsche-wiring-diagrams.html

Talk soon.

Hey FSR,
My problem all of this time was my catalytic converter was clogged... I separated the pipes just before the cat and Wha... Lah! She started right up! It was all filled up with lava rocks and she couldn't breathe! My OE cat looked like new on the outside but it was very OLD on the inside.
Maybe you should try cracking yours open.. I can't believe my car was laid up for a year with such a stupid thing... Oh well.. I learned the hard way.
Thanks for all of the help everybody.
Good Luck FSR

fsr
Keep at it - you'll get this fixed some day.

I'm not clear on what you're doing with the washer vs the speed sensor. Since I haven't done it I just am not sure of the process but the way you've described it doesn't sound like the way I've thought of it.

Also, I'm not clear on if you're injectors are good or not. I may have missed it somewhere. Have you removed them and had them cleaned?

One more thing. If I had spent this much time on the problem I would probably be willing to take it in to an expert. Of course this depends on where you live but it is always an option.

She runs... Better than ever...

Well, now the real story... When I was chasing down the problem a few weeks ago, I pulled the intake thinking I did something wrong. Turns out, when I put it back together, I must of doubled up one of the intake gaskets.. It was dark, I was rushing.. So I pulled the intake for a third time and resealed....she fired like it was new. Started on the first crank.

So, in summary, the gap was wrong on my sensors and before I finally re-gapped them, I caused an intake leak trying to chase the problem. When I re-gapped the sensors, I noticed no more popping out of the exhaust only through the intake. So I did my pressure test on more time and found the leak.

Thanks everybody for your help. You might not see me for a while because I am worn out with 944 stuff! Just kidding.. now on to electrical problems..

BTW, it only took 38 post! 40 was my limit:cool: