So I just finished up the oh so fun job of replacing both the timing chain assembly as well as the thermostat housing and now I cant get it to crank over. I have good battery power, the dash and all the accessories (windows, etc) works, but when I go to start the car I hear a servo motor but it doesn't crank. The motor turns over by hand fine. So its the starter getting energized, but not sure why. I checked the wires to the starter as the got stretched and there are no nicks or cuts. Not sure if the ECU is not sending the signal because of some other problem, or there is a problem with the wire going to the starter.

Any thoughts on where to start trouble shooting?

 

based on the fact that you have a raced prepped Porsche, I'm assuming that you know more then I do about working on cars (setting timing is still a mystery to me)..but my immediate reaction is bad timing?

 

Thanks for the reply. I don't think it is a timing issue because that starter is not getting energized. I used the factory tools (cam and crank locks) while doing the timing chain job and have verified after turning the motor by hand that the timing is spot on. Unless there is something with the alignment of the VANOS that I don't know about.

I checked and the trigger wire is not getting energized when the start button is pressed - just a little stray voltage which is typical. The problem is I am not sure if something is wrong with the trigger wire (it go a little stretched before I disconnected it) or if the ECU is not sending the signal for some reason. Very frustrating to do all that work and not have it even crank!

 

again, sorry if my suggestions are way off base. I'm always trying to learn more and like troubleshooting lol I really wish I had taken mechanics classes in high school.

Have you doublechecked the belt tension? Could the alternator not be supplying enough voltage?

 

Did you reconnect all the sensors when you removed stuff for doing the thermostat? All the sensors in the intake tract for example?

 

^^I agree, if you don't have the temp sensors plugged into the t-stat it will not start, as it thinks the car is severely overheating.

Did you reconnect the large ground strap to the engine mount bracket on the timing side of the engine?

There is also a rather large gauge wire that runs down the side of the engine on the timing housing to the starter that you would have had to move out of the way to get the engine mount bracket out of the way. Did you somehow damage the wire and create a short to ground?

On an off note, the 944 is in my top 3 arousing Porsche's list.

Nick
Detroit Tuned

 

The Altn. doesn't come into play on a starter motor engagement/crank. Once the engine is running, you want the charging circuit to work, so now it's time for the Altn. to work.
Even if the OP left the fan/serp. belt off, the engine should still crank and start for almost any normal engine design.
Hope this help build your car knowledge..

 

I double checked all the connections and they all look good but I am going to probably remove the airbox and intake hoses to double check - unplug and re-plug everything as there are a lot of connections and its possible one is not fully seated. Both ground straps (big one to the engine mount and small one to the post on the valve cover bolt) are good so its not that.

Does anyone know of a pin out chart for the ECU so I could check power at the output to the alt trigger wire? Just trying to figure out how to eliminate a possible issue with the trigger wire itself.

I'm also going to snag a obd code reader and just see if it connects ok to the ecu. Thanks for all the suggestions! I am all over doing mechanical stuff but hate tracking down electrical gremlins like this!

 

I'm not being smart about this. Honestly I'm not but I've done this before. You pressing the brake pedal ?

 

Not a bad question at all, but if it is a manual is the clutch depressed fully?

And secondly, is the clutch safety switch in place on the pedal lever? They have fallen out before and will keep the car from starting, seen it several times.

 

I have accidentally kicked off the wiring to the clutch safety switch with my foot, you problem mimics the clutch safety switch wiring harness loose or disconnected.

 

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