Help me diagnose - poor idle/rough running/low power from engine

[nynor]

Originally Posted by 951Boost

Pleeease don't put dielectric grease on the contacts. It's an insulating substance not a conductor.

But don't take my word for it, read for yourselves;

http://en.wikipedia.org/wiki/Dielectric

I know folks have used it "for years" without any problems but that is because if you use it lightly when the contacts engage they tend to scrape the grease off. If they are a bit loose and you get enough of this grease in there it will tend to increase the resistance.

It actually works very well in spark plug rubber boots and others as it keeps the boots lubricated (does not break down due to electrical charges) and prevents voltage leaks.

that is correct. that is what the word 'dielectric' means. which is also why i put it on my connectors. it prevents electricity from going where it shouldn't and it keeps water and corrosion out.

http://www.jamestowndistributors.com/userportal/show_product.do?pid=8196

[many944s]

Hey Jeff,
Just seing if you had resolved this issue yet?

[Porsche-O-Phile]

Hi, nope. The poor 944 has been sitting since I asked these questions and I haven't had time to look at it. I am however planning on getting into it this coming weekend (I actually have some time now). First I need to get my motorcycle out of my garage which is in the final stages of a LOT of upgrades and then I'm going to roll the 944 in and get this thing fixed. Once that's done I can get back to focusing on my 911... *sigh* too many projects...

Anyway I'm going to follow the advice here and check the injector flow rates first, spark secondly at each plug and then if those come up good, focus on the sensors.

I miss my 944 and want it back so I can enjoy it again!

[AKCJ]

Wouldn't hurt to check the plug at the AFM - mine was gunked up and causing trouble. Easy fix to clean it up. GL & let us know.

[jakethetech]

I myself am having some issues with a hard idle... But one thing added on, my idles jumps from 1000-2000 rpm's at least every two seconds... The surge is killing me... And it backfire and runs harsh as well.. I am currently working on it. I just had to rebuild the DME and I also own a Oscope... I do believe its something to do with throttle sensors. I had another car that did the same thing, and one TPS took care of it... I will let you know my findings..

[Brando]

Also check your grounds. That can be a symptom of erratic gauge behavior.

I also second checking the speed/reference sensors. Checking those without an oscilloscope is hit or miss. Without seeing a graphical analysis of the voltage output you can't be 100% sure

[my1st911]

[QUOTE=Porsche-O-Phile;4025801]WIN FREE PARTS FOR CORRECT DIAGNOSIS!!!



-Idle is a little bit rough (kind of like maybe one cylinder is intermittent?)
- Fuel efficiency/MPG gauge (which is normally all the way to the right at idleoccasionally "twitches" to the left in conjunction with the rough idle/misfires.
- When you put your foot on the accelerator all the way down (WOT/floor it), the engine will bog down and "pop" loudly once or twice or possibly stall out completely. In any case, it feels like it isn't good and probably not a great idea to continue doing.
- If you put your foot about 1/3-1/2 way down, the RPMs will come up, but very slowly/gradually. The engine doesn't quite sound right - more like a Honda lawnmower than a Porsche.
- Extremely difficult to drive due to lack of power/engine not wanting to "spool up" & roughness/misfiring occasionally
Here's what I've checked so far:

- Confirmed fuel pressure at the front of the rail (flows when key is "on")

- Put some Seafoam in the fuel to loosen up any crud


All these things to me point to fuel pressure. You said that you had fuel at the rail, but if the regulator isnt maintaining proper pressure during engine operation, then you will feel all these symptoms of poor idle, slow to accelerate, lack of power ect. Also my other thought is the timing is a bit off either due to a timing belt that jumped tooth or too, or maybe the rotor is not tightened down or rotor is somehow not positioned properly. I would look at fuel or timing. Most people have way more 944 experience than me here, so I am sure they have good suggestions, but as a tech on all different kinds of cars I would check timing and fuel pressure

[nynor]

you have one or more bad injectors, or possibly something to do with the sparkplugs firing (cap/rotor/plugs/wires). you can confirm by pulling and replacing one ignition wire at a time while the engine is running (if you are brave), or by pulling one and starting the engine. when you pull a wire and there is no difference, you have found the culprit, although there may be more than one. my friend's 944 would actually run on two cylinders and sounded/behaved exactly as you described. two of the four injectors were not firing at all and were found to be bad.

[pdx944]

I think its the DME.

[konan]

I say it is catalytic converter. Just disconnect the header and test it.

[Taz's Master]

Jeff, it is real easy just to pull the distributor cap and check and make sure that everything is tight and right underneath. I'd start there and be certain that the rotor is secure, the cam bolt tight, and the contacts all clean before getting into the more involved procedures.

[Porsche-O-Phile]

LOL! I forgot about this thread - I have a similar problem with my Benz (exact same symptoms) and I couldn't remember offhand what the problem was with the 944, so I came on here to check. It was the speed/reference sensors. Car runs great now. I owe someone a free something-or-other whoever said it first...

[AREA951]

Tps and or vac leak.can you hear a click when you open the tb by hand.

[Porsche-O-Phile]

Nah it's long fixed. It was a bad speed or reference sensor (I changed 'em both). The repair was extremely simple actually. I'm in a similar situation with my Mercedes right now so I've got to go and get a code reader to figure out which sensor has gone bad. Too many silly-azz sensors in cars these days. I wouldn't be the least bit surprised if it ends up being whatever the corresponding sensor(s) are in a Mercedes SLK to the Porsche 944's speed/reference sensors. Virtually the same exact symptoms, which is what led me back to this thread... Anyhoo - gotta' go get me an OBD2 reader.

Moral of the story - if your 944 engine is running like poo, check your vacuum lines, your distributor, your speed/ref sensors.

[looneybin]

so what do i win !!!!!

[mikseymono]

Holy thread resurection..............

Other than the 'pop' these are my symptoms. Have tried an exhaustive list of fault finding but no joy yet.

I thought that with a faulty speed/reference sensor the car wouldn't start. I have tested as per Clarks but no Oscilloscope. Just trying to sum up the 'collective will' before playing parts lotto.

Thanks,

M

[djnolan]

What did you conclude from this thread, maybe you should start a new thread on your specific issues...

[mikseymono]

I was just hoping somebody out there had similar issues and was spurred on by this thread to fix it. I have tested a fair number of parts on my car recently and whilst the sensors appear OK as per Clarks bar the oscilloscope, having read this old thread this is what I am experiencing.

Just hoping someone can confirm this is the likley culprit before I spend more money on parts!

Thanks,

Michael

[mikseymono]

OK...so..managed to get sensors out...not too bad.....the one nearest the bulk head in hole 'D' was badly eroded on the top as in it was rubbing against metal. I gaped new sensor as per Clarks. I stuck an 8mm thick cut up credit card to gap them. I cranked the engine. Straight away the tacho jumped up to around 4500 on start with no foot on accelaration...first time I have ever seen that...exciting, engine felt much more alive.....however there was this high pitched metal grinding whine. Sure enough I checked new sensor and the new one was eroded on the top as well. It turns out the aftermarket one is slightly...maybe...1mm longer than the OEM.

There does not seem to be the amount of play on the up down motion of the bracket on mine against this instruction vid https://www.youtube.com/watch?v=-MbghejYiqk

I have now put the old one back on as I have no more!

Convinced it is the speed sensor that is the problem. So question is, how hard is it to gap and if the sensor was scratched eroded would this make the difference? Was a bit adverse paying top whack for OEM Bosch sensor so bought these instead https://www.ebay.co.uk/itm/CRANKSHAFT-S ... 2749.l2649

Thoughts please.

Thanks,

M

[zedsn]

I can't see what you bought sensor wise but people were running bmw ones at half the price of a porsche ones. The only difference are the plug in lines are longer.