Hard/No Start After Refernce Sensor Project

[fsr224]

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.

[Rasta Monsta]

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.

[fsr224]

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?

[Capt Squid]

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.

[fsr224]

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

[Tervuren]

Originally Posted by fsr224

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.

[fsr224]

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..

[fsr224]

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

[fsr224]

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..

[AKCJ]

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

[Harriet03]

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

[Rasta Monsta]

Used the washer technique on the wrong sensor?

[kmakovac]

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

[fsr224]

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!

[Cocacolakidd]

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.

[fsr224]

Thanks, Good catch!

[fsr224]

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!

[Ga 951]

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

[fsr224]

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!

[Rasta Monsta]

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)?