I have been wrestling with a loss-of-power/stalling on my D2 for coming up on 2 months now ('04 HSE with 190K miles, stripped to bare block and rebuilt with flanged sleeves at 128K after a slipped sleeve). I've posted several threads already on it and have gotten lots of help.

Earlier this week I finally smoke-tested it for vacuum leaks (what someone recommended I do first -- but I'm a guy, so why follow good advice) and found a big one one at that quick connect elbow from the EVAP purge valve to to the intake manifold (the barb had basically disintegrated).

Fixed that and all seemed good, so took it for a test drive, and after 5-10 miles the same loss-of-power/stalling symptoms came back, and I barely managed to nurse it home, stalling a couple of times along the way.

I put the smoke machine on it again (a homemade paint can model) and noticed that there appears to be another leak: it looks like smoke is now coming out from underneath/around the accelerator spring. (see pic). Given how much smoke came out from the broken elbow on the opposite side of the throttle body, I am thinking I might have missed this the first time around.

Could I have a leak at the throttle body shaft seal (I am guessing it seals with an o-ring)? If so, can it be repaired? Has anyone done it (replaced the seal on the throttle body shaft)?

And if I have to replace the whole body, is the 1999-2002 4.0 body the same as the 2003-2004 4.6 body? (Logic would say "no", but that never stopped the British from marching to their own drummer and doing it "their way" -- apologies to all the nice Brits on this forum, that unique style of quirkiness is what makes you special.)


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I would not think you could lose enough of anything from there to cause your problem. 1 thing that occurred to me as I read this, check the torque on your intake manifold. When I fixed a coolant leak, I found several loose bolts on mine.

 

Thanks for the reply.

Another person on this forum mentioned those bolts as a possibility as well, so must be more common that it seems it should be. So checked and they were snug.

And there was no smoke from anywhere around the plenum base -- and when we first did the rebuild (seven years ago), we had smoke pouring out of the rear of the camshaft valley gasket when we smoke tested it after assembly so I know what a leak looks like seeping up around the intake manifold.

I note that when I put stress on the shaft laterally by pulling on the cables -- as would happen when pressing the accelerator -- the leak increases as well, perhaps pointing to a worn bushing that is in turn creating the vacuum leak.

Would help if someone has had a similar issue and verify it before I go and buy a used throttle body.

 

THOR aka Bosch engine TB's on a 4.0L or 4.6L = identical. Only the intake tube connection on the MAF side is different along with the MAF housing itself between a 4.0L and a 4.6L. MAF sensor itself = once again identical.

 

Just ordered a throttle body from LKQ from a vehicle with 100,000 miles.

Weird that they went a few millimeters larger on the MAF tube-to-throttle body intake joint and that was the only real intake change from the 4.0 to the 4.6.

My son broke off the IAT valve connection on the section of intake pipe 4 or 5 years ago, and I got lucky that the junkyard D2 I got one off of was an '03-'04 that matched (lucky, because I didn't know this quirk between early and late D2s, so wasn't looking for it).

Also, I have no O-Ring on that MAF tube-to-throttle body intake joint, so I have ordered one of those as well. Step-by-step, I am renewing just about everything on the top of the engine in trying to fix this problem.

After smoke testing and finding only that leak at the throttle body shaft, I buttoned it all back up with the leaking throttle body, and the problem persists: when initially started and warmed up (first 5-10 minutes), it runs fine, but after it runs for a while (more than 10-15 min), it will still idle but will hesitate, nearly stall and sometimes make that muffled detonation sound when I try to actually put a load on it by pressing the accelerator.

Could something in the engine compartment be heating up enough after running a while that it is expanding to create a vacuum leak or some other problem.

In all the testing I've done over the past 7 plus weeks, I have only put 25 miles on it total, so in the category of the most improbable, I was wondering whether it might be that I might just be working thru some bad gas (water in the combustion chamber can cause pre-detonation, right?)

I have a pretty good ODBII reader that can do live data streams, and I've looked at fuel trims and they look good. And it is not throwing any codes, so I am ruling out fuel injectors (a bad injector would throw a code, even if just a misfire code, right?).

Frustrated that I thought I had it beat at that first vacuum leak, but going to keep at it.

BTW Beaumont, are any of those D1s of your manuals?

 

Nope all mine are auto's, but my friend has 2 5 Spd D1's currently. For the kind of driving I do and off roading the 4Spd HP22/HP24 has never let me down.

 

Detonation sound with no misfire is odd, my 1st thought is really bad fuel but that does not match up.

I am thinking electronics, they often get squirrely as heat builds - CPS, Coils or Camshaft sensor would be my 1st guess. BUT you have done a lot of parts replacing and I have lost track.

It seems to me a dodgy camshaft sensor might do it without throwing a code, if it is sending a erratic signal. But I am not sure if they can fail that way, they should drop you into a form of limp mode.

Bad cat possibly ?

 

I had 1 generic CPS act odd and cause the engine to shutter on/off totally at random. It then decided to fail completely while out on my anniversary dinner... Wife wasn't to thrilled, but I got her swapped out (had a new Bosch in my spare parts kit). Wife just drank another Margarita and we were good to go!

 

My new CKP sensor is Bosch. And my tach works fine, so scratching that for now.

New Bosch coils, wires and plugs (and plugs all looked good, not wet or oily, so no head gasket, piston ring or related compression issues-- see below), new Bosch MAF sensor, and fixed leaked at that purge valve-to-intake manifold quick-connect.

Only an apparent vacuum leak left is at the throttle body shaft.

I am putting in a new TPS and then a underdash fuse box today: didn't realize how much electronics is integrated into that fuse box (my '73 911 has 10 total fuses in a simple fuse panel).

Once the new used throttle body arrives, that goes in next.

Last thing I am doing is a CMP sensor as that seems like it'll be the most work (haven't ordered that part yet). And I would expect a bad CMP to throw some codes, yet none.

But given that the symptoms really express themselves when the engine compartment (not just the engine) is well-heated up, it could well be the CMP.

I'm being philosophical at this point: once done with all this, if I do manage to solve the issue at hand, then I'll have a D2 ready to go another 100K miles.