Rough Starting - Backfire Grrrrr!

ae1969 · 06-22-2003, 07:35 PM

SO I was getting a strange oil leak in my NA.

Took me a good day to find the problem.

The intake valve stem seal (on #1) was completely off!!!! Oil was being shot in through the intake, and then shot out the exhaust.

The inside of exhaust manifold (in #1) was covered in oil!!!...

So over this weekend I pulled my Camshaft housing off. Replaced the valve stem seal........

Now I fire her up........ and its backfiring and just wont stay running. If I hold the gas slightly it revs nice around 2-3 k. If I let the gas go. She shuts off. As I try to start she backfires and frankly sounds like ****.

*** First thing I thought was that I screwed up the timing. Nope all marks line up. Mark on Camshaft hoursing, flywheel (top and underneath). I turned the engine over by hand at least 10 times setting the tension on the timing and balance shaft...so I am 99.5% sure that its fine. Pulled the covers off and it still all lines up.

The car was running fine (considering how much oil was being spewed through) before this.............Idle was fine no other problems........except the symptoms that led me to investigate, slight hesitation at accelaration, oil smell, smoke on letting of the gas (similar to valve stem seals going).....

Tomorrow I will do a leak down on #1. Probably on all the others just to be sure.

NOW what if anything else could this be?????

- I swapped spark plug wires .... same issue.
- timing is dead on...

Thanks,

fast924S · fast924S's Garage

Maybe something is wrong with one of the valves not closing all the way. If I where you I would do a leak down test on all cyclinders. I would also check all your cacuum lines and sensors just to make sure. Was there anything wrong with your distributer and rotor, maybe its arcking. Sorry I could give you a dead on answere. Good luck

MrPants · 06-23-2003, 12:19 PM

if oil was getting all the way through the exhaust, maybe the O2 sensor or another sensor got all junked up and isnt working properly

ae1969 · 06-23-2003, 12:41 PM

Ok.... more info. Leak down is fine on all 4.

She is starting........but I have to keep my foot on the gas to keep it running........... If I keep my foot on the gas it runs steady over 3k , if I let it go she complete stalls. Rough idle and sounds like she is missing or backfiring under 3k............

* Everything was running fine prior to the tear down. Something is not right... Just have to back up and take a look at everything I touched....

ae1969 · 06-23-2003, 01:48 PM

Quote:

Originally posted by FR Wilk
vacuum leak?

I am going in to take a look at that right now.........

ae1969 · 06-23-2003, 03:25 PM

Vacuum lines look fine..............

next ?

Roger Hall · 06-23-2003, 05:29 PM

Quote:

Originally posted by yo mama
if oil was getting all the way through the exhaust, maybe the O2 sensor or another sensor got all junked up and isnt working properly

Couldn't hurt to disconect the O2 sensor and see if there is an improvement. Would the oil get near the fuel injector? Is it possible that an injector is fouled up from all the oil? I relly have no idea just tossing out idea's

ae1969 · 06-23-2003, 05:40 PM

Quote:

Originally posted by Roger Hall
Couldn't hurt to disconect the O2 sensor and see if there is an improvement. Would the oil get near the fuel injector? Is it possible that an injector is fouled up from all the oil? I relly have no idea just tossing out idea's

I will unplug the O2.......and see...........

I pulled the injectors out earlier they are clean and seem to be fine. I will test them for flow tonight....

gggggggggggrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrr..... .........

fty · 06-24-2003, 06:53 AM

o2 ussually wouldnt cuase the engine not to run..

ae1969 · 06-24-2003, 07:03 AM

OK here are the symptoms.

1. If I just turn the key.... she starts.... and sputters out immediately...

2. If I turn the key.... she starts.... I give it gas....if I rev it past 2-3k she revs nice and clean.....but it is hard keeping her at that. She surges and lopes all over......but at high revs NO misses, pops, or sputters..... If I let the gas go completely.....she will rev down under 2-3k and sputter, backfire, misfire, pop, blurb, and finally stall out.

The only way she runs is with me massaging the gas and keeping it over 2-3k but even then she surges when I touch the gas.

Thanks for your help.

zehnd · 06-24-2003, 10:40 AM

Long shot. Is your connection into the AFM secure.

carsontc · 06-24-2003, 06:08 PM

it's pretty easy to mess up that intake manifold gasket

ae1969 · 06-24-2003, 06:27 PM

FR...........I thought I could have a massive intake leak...........SO I pulled my intake again....... she seems to be sitting fine.

NOw some questions...

1. I checked the AFM.... all the specs are right except where it says that it should hit 8 Volts or more. On those tests I only get 4-5 volts.

2. I checked the TPS.... all specs dead on.

3. I checked the Temperature sensor.... Now this sensor must have a bit of a problem. If I wiggle the prongs I get ~1.6 kohms... within spec. Sometimes she will have no reading. This sensor affects the DME on wether its cold and it should run rich or lean??? Could it cause such extreme running conditions? We are talking extreme. You can't idle this car!

4. SO I ran air though the intake boot......I can hear some swooshing under the intake........ It sounds like the cold start valve ( I believe its called). It may be the problem not sure.... have to take a closer look. I can definitely hear some air? but I can't feel it coming out. ??? How do you check that valve....?

5. I checked the fuel rail. Pressure good. All injectors firing nice sprays.... never realized that it did not fire one injector at a time... uhmmm you learn something new everyday.

Egad....... this is such a pain!

Thanks!

Wolf1 · 06-24-2003, 06:35 PM

Quote:

Originally posted by ae1969

3. I checked the Temperature sensor.... Now this sensor must have a bit of a problem. If I wiggle the prongs I get ~1.6 kohms... within spec. Sometimes she will have no reading. This sensor affects the DME on wether its cold and it should run rich or lean??? Could it cause such extreme running conditions? We are talking extreme. You can't idle this car!

Alex, the temp sensor could be causing gross over-fueling. Not sure on the 944, but on many EFI systems when the temp sensor goes open the computer see's that as -44 degrees Fahrenheit. Most cars wont idle with this reading especially when warm.

ae1969 · 06-24-2003, 06:45 PM

FR - read your site on the AFM : Ok my readings are good for the LATE AFM...........who would of known! Thanks for the info on your site FR.

Wolf........ It may be part of the problem. I have to read wether I should short it to try and test it...... Thanks . WIll check this out.

ae1969 · 06-24-2003, 06:49 PM

From Clarks Garage...........

"If the car starts when cold but, idles rough or does not want to stay running, this can indicate a problem with the engine temperature sensor. When the engine is started cold, the engine temperature sensor sends a signal to the DME control unit to provide a richer mixture. As the engine temperature sensor starts to fail, it sends a higher than actual temperature signal to the DME control unit. The DME control unit leans the fuel mixture thinking the engine is at normal operating temperature. This causes the engine to run rough. As the engine warms, it not longer needs the richer cold idle mixture and the engine runs smoother. "

Now how can I fool this sensor to test it out?

I think I will pull the temp sensor and see. If I can fix it............

AFJuvat · 06-25-2003, 06:19 AM

Sounds like one or more of the following:

Agree with temp sensor - they are easy to damage when working in the area (like removing intake etc.) - No real way to fix it - replace. Think they are around $50 USD.

For testing, if you have the ohm value for the sensor cold - pop a resistor in the sensor plug of the same value

Possible cracked\broken\misrouted vacuum hose. I'll have to pull my vacuum hose diagram from home and send it off to you. (damn hd failures!)

Never seen a bad o2 sensor disable a car - will cause a little funky running and poor economy.

This is one to ponder over lunch

AFJuvat

ae1969 · 06-25-2003, 06:32 AM

Mother Juvat......

You know.....

The more I turn her over the more it sounds like the timing is advanced...........

She idles like crap low (and I mean like crap!.. she stall out)....I rev her up and she evens out??

Now I know the the timing is adjusted by the computer.... and 2-3 teeth (if that) either way is buuuuh byyyyye valves..............

But what happens if you are a tooth either way?

How much can the computer compensate? Can it adjust the timing 1-2 teeth?

ae1969 · 06-25-2003, 09:19 AM

FIXED!

Ok so the problem was ..........

A massive intake leak. FR mentioned it......and I posted about a swooshing sound under the intake. Should of investigated further at that point!!!!

(Tip .... running air through the intake boot lets you find these leaks)

It was the hose that attaches under the intake (cold start valve?>). It must have gotten squished at some point......... nasty tear.

SO I replaced it. Fired up and idled fine.

Thanks for all the tips.....

I learned a lot about all my sensors and how they are inter-related............. asides being a MAJOR PITA........ it was quite educational!

Thanks again!!!!

P.S. I searched so many posts with similar problems and no-one ever replies back with what the outcome was.... I am guilty of this as well, but never realized how many posts are just dead ended.... just a reminder for everyone to post the outcomes of their problems.

carsontc · 06-25-2003, 09:41 AM

Quote:

Originally posted by ae1969
FIXED!

P.S. I searched so many posts with similar problems and no-one ever replies back with what the outcome was.... I am guilty of this as well, but never realized how many posts are just dead ended.... just a reminder for everyone to post the outcomes of their problems.

so true...I bet 90% of the folks asking questions stop posting as soon as it's fixed without reporting back

(until their next problem pops up)

if the feedback was provided we could start to build 'knowledge base' where anyone could ask a question and automatically be provided appropriate previous post each with a confirmed 'fix'

not to mention it is just part of being a good Porsche 'forum citizen'

(maybe before ‘advice’ is given we should check the writer’s previous posts to see their feedback record…rate them like eBay…with a positive, negative etc…hmmm)

thanks for the positive feedback