Chris Lockhart

Like the subject says, it recently started to have an irregular idle, which progressed into the engine trying to die under decell. Seemed to run fine at more aggressive throttle openings. Then it started to miss badly at random times. I put in a new O2 sensor, as well as a new driver's side fuel pressure dampener, partly because I already had these parts and was going to change them anyway. Drove the car around for a few miles and it ran strong. No miss, and while the idle wasn't perfect, it didn't die upon decell. Grabbed a shower, and my wife and I were gonna go for a cruise, and it immediately starts acting up again at idle, and upon decell. In general it will run fine at larger throttle openings once you have taken off, but even then there is an occasional stumble out of nowhere. I may be mistaken, but I could swear that the engine stumbled whenever I turned a sharp curve, or hit a large bump. (I wish I could see the fuel press gauge on the rail while driving, to see if the stumble coincides with any fluctuation in pressure.)

Now possibly on a related note, the PO sent me an e-mail regarding the Bosch 044 pump, and a link to Andrew Olson's disentegrating pump issue thread here on Rennlist. I haven't dove into the in-tank pump yet to investigate, because I would like to have an actual plan before I start pulling pumps out.

Does any of this sound like it would possibly be caused by the in-tank pump? The feeling that curves/bumps could be affecting the miss/stumble made me wonder about the fuel delivery system. Any and all help and guidance is appreciated. Please bear with me, as I have been away from 928'ing for almost 5 years, and it has beeen slow getting back into trouble shooting. TIA,

Lizard928

Have you done a brain reset since you put in the new O2?

AO

Hi Chris... I believe the in-tank pump could very well be causing this issue - sounds like it's running lean/ . The issue is if the in-tank pump is now restricting flow (which it very well could be) the 044 pump will cavitate which can lead to all kinds of issues.

Pull the in-tank pump (it's trashed for sure) and stick in a stock strainer at a minimum or get one of the 044 strainers from Tim Murphy.

The only other thing that comes to my mind is the grounding of the LH harness. There are two bolts under the rear of the intake where the harness is routed and grounded. If those are loose, it will and can stumble especially on curves and bumps.

Bill Ball

It would sure help if you had a wideband O2 installed to figure out is this is a fueling issue, or at least a fuel pressure gauge.

Maybe you are aware of my idle story with the Supermodel. Cold idle OK, once warm, a good miss. So, interpreting this as heat-related, I blamed warping of the base plate of the manifold, which is rather thin aluminum, causing a vacuum leak, leaning out one of the cylinders until it missed. I braced the manifold internally with bolts adjusted to match the height of the sidewalls in every bolt hole Andy had put in the upper plate. The sidewall height was exactly 1", so I also used 1" spacer tubes around all the manifold bolts. Finally, I cut 5/32" spacers to support using the stock gasket under the bottom plate, providing about a 20% crush (not more due to metal inside the stock gasket). That worked well.

BUT your issue sounds much different. The only time I had oddball driveability issues outside of the idle was when I had moved the FI grounds away from their stock location. They didn't like that. Andy wanted them to be lengthened and put in the stock location when the rest of the harness was pulled to its new location of the MAF and throttle. He was right.

AO

+1 on getting a WBO2 reading or a FP gauge reading.

I will most likely bring my portable WBO2 sensor with me to SITM, so if you still haven't figured it out, we might be able to take a stab at it depending on my state of sobriety, the weather, etc.

dprantl

Take out the throttle/MAF/Idle Control Valve/intake pipe and look at the hoses that connect the valve to the intake pipe very carefully. On our cars it takes 5 minutes You just may find that the long rubber hose has a nice big crack in it, especially if you still have your air pump diverter valve installed.

Dan
'91 928GT S/C 475hp/460lb.ft

Chris Lockhart

Lizard, I disconnected the battery for about 3 hours, then hooked it back up and drove the snot out of it. It ran fine with minor fluxuations on idle/decel.

Andrew, is the strainer the entire assembly? I was looking it up on 928 Specialists site, and I think it was like $51.00 for the fuel tank strainer.

Bill/Andrew, I do have an LM1 but have not installed it yet. It's still in the box. Came with the car.

Dan, thanks. I will check it out when I get home.

All, I checked the fuel pressure, and at idle its about 32-35 psi, and reving it up (no load) doesn't change it much. maybe 35-37 psi.

Lizard928

32-35PSI is low for an S4.

Contact Murphy he has the proper 044 strainer and I am pretty sure he can get it out fast too.

Bill Ball

+1 to what Colin said. Andy's design usually included an 85/6 FPR which would set idle FP at 38 PSI, still lower than 87+ by about 10 PSI. This was before Sharktuning, and this was how Andy dealt with using 30 lb injectors in place of 19s. It worked reasonably well, as the 85/6 FPR was somewhat boost responsive. At fuel pressure around 30 PSI the injectors will quit firing. So, something is amiss if all you can muster is fuel pressure that low. Some people substituted Kirban adjustable FPRs in Andy's kits, in which case you should try adjusting the FP.

DR

Hi Chris ole pal,

It is so great to see you posting about YOUR 928 once again...even if it is about some issue(s). :-) Can't wait to see you at SITM once again driving YOUR 928!!

First off, concerning the strainer, even if it isn't the issue, get the strainer from Murph that Andrew mentioned, all of the Porsche variations are crap.

Yes your FP is low (but I have seen Andy run some that low, depending on Inj size)...BUT this doesn't account for the intermitant variations you are experiencing. More so than the low FP, I am suspicious of the small variation in FP when reving it up. This makes my suspicion of a vac leak in the intake system some where even stronger, or even something is not tightened securely (which could explain the large bump, sharp curve symptoms).

As Bill mentioned the older SM intakes are notorious for leaks in various places, and those can change to various degrees depending on temp etc..

You would be surprised how well the SC setups will run on a 928 at higher RPMs...even with a large hole in the air guide, plumbing etc between the MAF and SC unit (just ask Andrew...in private :-)

Honestly it sounds to me like you have multiple small issues, some are likely ignition and/or wiring related, some "air/vac" related , and some possibly fuel related.

Just as point of reference, it would be interesting to see what type of vac you have at idle (cold and hot), and even better if you know some one nearby that can do a smoke test on your intake tract (again hot and cold) it could answer a lot of questions.

Regardless, if you can't find and solve it before you come up, limp that bad boy up here..between the 928 Brain Trust at SITM, some with the added SC experience like Tony H, Andrew, Bobby H, Woody, Murf/Mike(if they get to make it, come on you slackers), Dave C. and a slew of others... we will get your situation figured out and most likely easily resolved.

BTW, I have an new Adjustable FP regulator, a Bell FMU, and a host of other SC goodies here if you need them...consider any of them a "Welcome Back to the 928 Ownership" present(s).

I also have piles of SC developement parts that are going to be "dumped" at our Sale on Sunday, including a bunch of the older SuperModel era parts.

BUT as others mentioned, at some point in time we need to drag your SC install into the 21st Century, dump all those "manual" tuning devies and get you SHARKTUNED. If some of the guys have some ST files that are close or even the same as your SC configuration, we could use that and get you started on that path quickly.

As a matter of fact, "Mr SharkPlotter" himself will be here doing a presentation on a new Sharktuner product, and to spread his vast knowledge of all things "SharkTuner" Saturday and Sunday ...and maybe, just maybe we can get him to use you as an example, especially if we have a "close starting point" with the above mentioned files?? (Hint Hint, Jim)

I hav dedicated ST Tuning Computers with PEMs on board here, and even if you don't want to spring for some PEMs at the moment for your computers, I have plenty of blank chips and a burner so we can cook up some new proms for you once we get a stable tune.

See ya soon,

Dave

Chris Lockhart

Thanks guys. And DR, all I can say is that you are a dear and valuable friend!!!! Any and all help will be appreciated at SITM. I plan to limp it up one way or another.

Oh yeah, on the list of uninstalled parts I have is a BEGI, that I have no clue how to hook up/set-up. Do I need this?

DR

Chris,
IF you decide to go for the Sharktuner option everything related to fuel pressre needs to go back to stock S4. i.e no BEGI etc.

AO

I do too and I have the remote WBO2 sensor, chip burner, etc that I will have with me at SITM.

But while Sharktuning a broken shark might get it running better, as soon as you fix what's broken, you'll have to re-tune everything.

DR

Sorry, I never meant to imply to use a SharkTuner to fix a problem, although they are very handy for diagnosing some issues...the ST discussion was for AFTER YOU fix the problem(s) Chris is having... HA HA!!

OH, Chris, it would be helpful if you can give us a rundown on which system configuration you have to the best of your knowledge...and a few pics might help too. This will help us track down some good ST files others may have that is close to your configuration.



See you guys soon,

Chris Lockhart

I will take some pics tonight and post them in the AM. Not really sure of what is what, because I haven't really gotten into it too much, and the PO did not have complete documentation. To the best of my knowledge it's the version 1.0(?) with the Jag/Eaton s/c, pulley'd for 8-8.5 psi (Gauge not working). It does have some sort of intercooler. Supposedly the s/c was rebuilt with new seals and bearings just prior to purchase in early Feb. Approx 1500 miles since then.

Listening to it idle this morning while getting fuel press readings, the s/c sounded pretty rough. Bearing type noise. Never heard that until this morning when cold. Not sure if it goes away once warm, as I didn't have crap for time before work to let it warm up.