911 sc starting issues

[adamr]

Hi guys,

been at it again today, cant find the filter here so cleaned up the rotor and cap, and checked all the plug wires, one was loose. It starts, idles around 500-600, but is backfiring allot thru the pop up valve, it stabilizes, but then it goes into an all out run-away up to 6k or before i cut the ignition. I have the air filter cover off, is this causing an issue>? if not why would it go into full throttle without the input from the pedal. It sounds beautiful when it goes off into full rev but puzzles me why it does that.

Can the plugs being bad cause the backfiring?


Stuck in Paradise with the only Porsche 911 on the rock and no help

Adam

[steves31]

You got a massive vacuum leak somewhere listen for any sucking noise

[adamr]

any where in particular to look for it, the hose on the distributor had come off but we fixed it and still doing the same thing. where are the other vacum lines.

Adam

[Dave Colangelo]

+1 for vacuum leak, the search function will reveal a chart of the vacuum system its up here some where. Trace all the lines. If they are all there and connected you may have a leaking line, I have found that the rubber degrades over time. You can get a wheel of the right size line for cheap, then replace all the lines.

Regards
Dave

[adamr]

thanks will do that, dont know where i would be without this forum and ive had the car for a week

adam

[adamr]

The only issue i could find was the distributor vacuum line was not on the back of the throttle body correctly, and the hose from oil vent tank to the rubber intake that goes from the air meter valve to the throttle body was loose.
I checked all the other lines that i could see and they all seem ok. Could that line being barely on cause it. I have not tried to restart it, as i dont want to cause any damage with the backfires and out of control revs

[Dave Colangelo]

With vacuum leaks although the line does matter a leak is a leak. I understand your hesitation to start it. The other thing that could be an issue is the CIS system. As I am fairly new to SC's as well I have not had much time to dig in to it, but I do know that it had some issues. From what I have read the system is very susceptible to moisture, if the car was sitting for a while an issue could have come up with it. For this a good place to start would be the injector pressure and fuel pump pressure. With how few miles you have on your car I would be very hesitant to expect any serious mechanical issues relating to timing and what not. This sounds like an issue related to either the vacuum systems, electronics, or fuel system.

Personally when trouble shooting this issue, I would go through the whole ignition system and check all the components one at a time. Take your time you will figure it out, some times its simpler that you think.

Regards
Dave

[adamr]

The car was running well up until the clutch issue, which makes me wonder whats up. I am not really worried about the backfires right now as much as motor just idling along and then just blasting off into 6000 rpm. is their a rev limiter that will stop it from over-reving? I cut it off before it makes it past 6500.
I just cant see why it launches it to red-line.

[adamr]

Is the throttle supposed to open at all when the clutch is engaged? When I push the clutch the throttle opens up quite a bit. I have not been brave enough to try start it without the clutch engaged.
EDIT: I had my brother come over, the throttle body opens to what would be half way to floor on the accelerator pedal. I AM Guessing this is NOT supposed to happen!
I found this digging thru the archives:

Originally Posted by SpeedracerIndy

An improperly adjusted clutch cable can also cause this symptom. Although, I don't' know why it would happen after sitting for months.

If there isn't enough bow in the bowden tube of the clutch cable it will rub on the throttle cam on the transmission. If it does this, every time you press the clutch petal, it will put pressure on the throttle cam causing the throttle to stick open.

Just another thought.

I had this happen to me this past summer during a PCA event where we did a ~100 mile drive with some very spirited driving. Every time I would engage the clutch, my RPMs would shoot up. The hotter it got, the worse the hanging throttle was. it made for a very frustrating drive.

[Peter Zimmermann]

The backfiring might be a lean condition due to an open butterfly in the throttle body. Then, once the injectors supply fuel the engine revs wildly due the the butterfly being open. Disconnect the throttle linkage at the throttle body and see if the throttle body lever snaps closed. If it does, start the car with the linkage disconnected and I'll bet it runs properly. Then figure out what is screwed up with the throttle linkage.

No, nothing in the throttle should change with clutch pedal action. Completely separate systems, which tells me that your throttle linkage might be damaged where it passes along the left side of the transmission.

[Dave Colangelo]

Sounds like you need some pedal box work, there are some nice threads and work through both here and in the 101 projects book on how to do so.

Regards
Dave

[adamr]

So the throttle being opened by the clutch cable basically could be causing the backfires and the revving. Guess ut nakes sense to check the obvious before ripping apart the motor

[Bob Kontak]

The throttle hardware runs right next to the transmission and in fact has mounting points on the trans case.

Get underneath your car and have someone press the clutch in and see where the screw up is in the linkage (as Peter says)

[pete3799]

Just so you know.....the reving and backfireing are two separate problems.

[timmy2]

The loose hose from oil tank to airbox will cause a huge vacuum leak.
When I bought my car, that hose was off and the rubber boot it attaches to was not seated onto the airbox . PO couldn't get it to idle at all! I had the car running the next day after sealing those 2 vacuum leaks.
Inspect all your hoses and connections as well, tighten the good ones, replace the bad ones that are cracked, worn or brittle. That should help reduce the backfire issue.
The racing is a different issue and it sounds like you have many things to check to cure that one.
"Can't find your filter here" either means it needs to be shipped to you or you can't identify it. Just in case it's the latter, your fuel filter is the big cylindrical silver thing in the picture with a red cap on it.

[adamr]

Thanks again,

Pete, i understand its two separate issues. I am going to change the plugs on Monday and see what happens.
Timmy2, I will put a hose clamp on the oil tank to airbox tube, its seems like its one of the biggest vacuum hoses on the car. Between that hose and the distributor hose it should be fixed. I cant source the filter locally will be placing as significant Pelican order soon

[Peter Zimmermann]

Please check post #10 again. Disconnect the throttle linkage at the throttle body...this will isolate the engine from the linkage. Once you've done that, you know what to spend your time doing.

[adamr]

Hi Peter, I totally understand the throttle issue, will source that on monday, and check the vacuum hose issue as well.

[Jdub]

I know you have a popoff valve, but can you get a finger under any of the screws holding the airbox to the engine? If this item is at all loose you will experience this problem.

But the throttle body sounds very promising to me.

[adamr]

pulled one plug and here is what it looks like, smelled like gas