Sputtering/Hesitation Problem...

[thewerxracing]

So, on the way to the race on sunday, I developed a sputtering problem under throttle in my 1984 944 N/A. The car is stock, minus a cherrybomb muffler. Also, the car spent the last month with the top of the filter box (with the element still sealed and in place) off. I put it back on that day for the racing sanctions rulebook.

The car would buck severely and hesitate. Even out of gear, revving it-- it would break up and not rev strongly.

Thinking it was a fuel delivery problem, and considering there was a intermittent whine from the fuel pump, I replaced the fuel pump and filter today, still there. So, I pulled the plugs to see what they look like. I took out the plugs and noticed #1(or the one closest to the front, not sure of the numbers) to have a little oil on it. The other three look fine, just used.

The wires and cap/rotor have been replaced less than a year ago. They look fine. I know the oily cylinder is firing because I pulled off the wire and it started to idle erratically, put it back and it idled fine.


I just did the plugs/wires/cap a few months ago. But I threw new plugs in today, same problem. No backfiring or afterfiring, though.
I have:
Replaced the Fuel Pump
Replaced the Fuel Filter
Replaced the Spark Plugs (properly gapped 'em, too!)
Cleaned the Mass Air Flow Sensor (using CRC)
Cleaned the K&N Element

So after looking around, trying to get a hint to as what this motor is doing, I have discovered a few things. Some may be irrelevant to this particular issue. But...

I pulled out the plugs to see how they look and throw a new set in. Plugs #2,3,4 Looked normal with about ten grand on them. Plug #1 looked rough. It had been covered in oil.

Plug #2


Plug #1



There was also a small amount of oil in the plug recess.


A bit of fluid in the J-Boot, as well.



The 25 years of **** that accumulated in the Throttle Body.


The Exit of the MAF. Cleaned, just stained.


Breather hose off the J-Boot.


Now, I'm not saying any of these are the cause of this, in fact I know they're not. But they have to be able to give someone a hint.

Tomorrow, I will be looking into the fuel injectors, perhaps some cheap gas killed one.

I can hold the car at a steady RPM and it will purr. If I fluctuate the Revs, it falls on its face, then bucks. It does this in and out of gear, so I eliminated a drivetrain problem. I don't think it's the DME because if it were, it'd be having the problem when I hold the Revs steady as well. Also, I dont think its a mechanical setting (Such as a timing belt), because, again, that would let the problem be seen when the car is iding, or under constant (not fluctuating) throttle.

Hmmm..

Any ideas? or any tests I can do to it to help you guys help me? I already missed last weekends race, I'm dying to get to this Sunday's event.

[tnporsche]

Does it do it when cold and hot?

[TibetanT]

Piston rings or valve guides on cylinder number 1 may be bad from this description and pictures.

That is my best guess right now.

[thewerxracing]

It doesnt do it when I first take the car out, but the problem developes as it gets warmed up.

And I knew it had to be a ring issue for #1, but that wouldnt be causing this, that's a whole 'nother barrel of fun.

[thewerxracing]

Well, using my billion dollar Snap-On scanner, I realized every part that said Bosch on the damn car was in spec. Pumps, Coil, MAF, fuel injectors. Everything. So I went back to basics...


After pulling the fuel hose off of the tank (the one leading into the pump) I noticed that it was not pouring out like it should be, something was clogging it.

After a quick shot of compressed air into the hose, the fuel now poured out of the tank. Good.
But whatever was clogging it is still in there, waiting to clog again. Bad.

Okay, how do I go about getting the crap (probably a cheap in-tank filter of sorts) out? Can I get a good look thru the top (where the sender for the gauge goes) hole, and perhaps throw a grabber down there to yank that garbage out? or does the bottom plug open more?

[TibetanT]

Be CAREFUL poking around with stuff inside a gas tank that is not completely FULL. One spark and kaboom.

What I would do to remove anything from a gas tank is:

1) Take it off the car.
2) Remove all the fuel.
3) Fill it with water.
4) Try and remove the culprit piece.

OR, take the gas tank to the experts.

[TibetanT]

Yes! You should be able to get a look at what is causing the problem by looking into the tank from the top.

My guess is, the sending unit end piece fell off for some reason. Rust maybe.

Has the gas gauge been reporting correctly the amount of gas in the tank? Just wondering, since it would be erratic if that were the case.

[thewerxracing]

Kinda. After I blew that hose clear with the compressed air, the gauge started to act up.

[thewerxracing]

And I think I'll drain that tank completely tomorrow. I really don't want to throw water through it though. Can I just drain it and blow the fumes out?

[TibetanT]

As far as I can tell from the documents I have read, with regard to fixing/working with gas tanks, that is not possible.

Why? Because there is always some residual gas fumes left within the tank which is why the experts who weld gas tanks always fill it with water.

The other reason why I suggested taking the gas tank off of the car is, if there is a problem, only the gas tank will be destroyed.

Good luck with that and I hope this helps.

[thewerxracing]

...only the gas tank.. and possibly my torso. =)

How hard is it to get the tank out? Does it require dropping the transaxle?

[John_AZ]

Originally Posted by thewerxracing

...only the gas tank.. and possibly my torso. =)

How hard is it to get the tank out? Does it require dropping the transaxle?

Hmmmm..............was this question a test?

Yes, you will need to drop the transaxle. You better have a very good 8mm hex for the coupler or you will be spending hours when you strip the pan head bolt.
The linkage bolt/pin is very fragile. Do not over torque. Support the TT on the rear cross member with a piece of wood. Check the intermediate shift lever for slop.

You should do a few WYAIT items.
Replace the old hoses on top of the tank.
Repack the 4 CV joints.
Since you track the car, you might want to replace the CV bolts.

GL
John_AZ
1988 924S + 1987 924S

[thewerxracing]

Thanks for everyones help!

I pulled the in-tank filter from the bottom. It looked like a clogged storm-drain, with 25 years of trash.

I discarded the old in-tank filter and left it out. Then I threw on an in-line filter from a 199X Chevrolet. (Fram Part #XXX (Not sure yet)). I put it in the hose before the pump. I'll throw some pictures up soon.


The car runs healthier than ever! Thanks again!

[TibetanT]

Excellent!

You know what, I had not thought of that filter...good of you to post the results so we all know better in the future.

Good for you...have fun.

[thewerxracing]

Here are a couple of pictures of the filter, showing how clogged it was, and my final product. Thanks again for the help!