FredR

Hi Bob,

Interesting- I remember Susan saying just how well that motor pulled- good to hear it is still "hauling ***" as it were. I tend to think of mileage in km so 150k miles would be in the 230k km range. For sure the Devek build had much lower miles on it.

Regarding your base problem once you have eliminated things like the vac connections you will need to widen your search. Clearly this is not a MAF problem so the hunt is for likely causes. So you have a cold idle that is OK but a warm one that is not holding. If the ISV were frozen that does the opposite- cold starts only work with some throttle applied and hot idle sort of works [the rest position approximates to that needed to support warm idle thus if the cable is disconnected it sort of idles when warm].

This leaves me wondering what might happen if the ISV is stuck in the partially closed position. This would cause you to have a low idle or non existant idle but then not sure what that would do to a cold start condition that requires more fuel. On carburetted modes this used to be achieved by blocking air flow to the carb to enrichen the mix- sort of like what might happen if the ISV were stuck partially closed perhaps? Either way if you have not replaced the ISV good chance that might be involved somewhere in the equation. Trouble with ISV problems is its an inlet manifold job off type of thing unless you can squirt something in there to see if it can be "degunged".

Hopefuly you will get some more enlightened inputs. Have you checked the idle switch contact? You should be able to hear that click as the throttle bottoms out or you can simply measure the wires for contact at the LH connector. If that signal for throtttle closed does not make it to the LH then the brains do not know to apply a controlled input to the ISV [or so I understand]. Just holler if you need the terminal numbers to check this.

Rgds

Fred

RET

Hello Fred,

Idle switch probably OK - display shows "0 liters per 100 KM" (display stuck in Deutsch... an old, old problem...) when decelerating on the highway, and the car idles happily >600-650? with the loaner MAF (RPM per the instrument panel - tough to accurately interpret...).

The old MAF and Bill's loaner idle well hot or cold, but the car will not idle well when cold with the newly rebuilt unit: it does not idle smooth and is barely over 500 RPM when cold and first started, and it drops quickly from there.

The loaner MAF and my old one would idle >800 when started cold and drop to the normal idle as the engine warmed.

My time is not my own for the next day or so, but I will get after this as soon as I can.

Thanks!

Bob

RET

I finally got around to fiddling with the new MAF again. No joy.

Recap: newly rebuilt MAF will not idle when the engine is warmed up (seemingly runs well on the road...), works great in Bill Ball's car but stalls in mine when it tries to idle; his loaned spare MAF seems to work well and my old MAF had no idle problems; my car has 30 lb injectors, set up and tuned by Devek (...6 liter stroked engine, EPROM with unknown maps in the LH, etc...); some time ago I had replaced the original AFPR due to a vacuum leak, and noted then that the fuel pressure was below the normal 55 psi w/o vacuum, but failed to record the value, and the new AFPR got set to 55 psi, but everything seemed fine (perhaps the old MAF was degraded?). It never occurred to me that there might me a reason for having an AFPR, and of course setting it to a lower pressure.

I have experimented with reducing the fuel pressure with the new MAF and got the engine to idle without stalling, but it would idle lower than normal RPM, and pretty ragged too. Perhaps my procedure was faulty, because when I finally gave up and put Bill's spare MAF back in, the idle was low and unstable for awhile. A few jabs on the throttle cleared things up, so perhaps I managed to foul the plugs, create a second problem, and obscured the results.

This was my process: checked dampers and AFPR for vacuum leaks, all good; engine warm; fuel pressure was ~55 psi w/o vacuum, and ~45 psi with vacuum at idle with Bill's MAF; put new MAF in, disconnected the battery for about 15 minutes, jumpered the fuel pump relay, and started the engine; as before, it would not idle; reset pressure to 52 psi w/o vacuum, and restarted the engine; it started fine, but would die unless throttle was used; I repeated this process (...and what a PIA adjusting this AFPR is!), reducing the pressure 2 psi each time; the car would idle when the pressure reached 42 psi, but not well, and at lower than normal RPM; I continued the sequence out of curiosity and with little conviction in the hope that the idle would improve; it did not. The pressure was 20 psi when I finally gave up. (FWIW, I had been told that the injectors would not work below 30 psi, but the engine still ran... well, sort of...)

All of the above took a great deal of time, with the engine running very rich at least for many of the testing sequences, so my next experiment will include an Italian tune up with Bill's MAF and then setting the AFPR to 40 psi with no vacuum before putting in the new MAF and starting the engine again.

In the mean time, I would greatly appreciate suggestions.

Thanks!

Bob

FredR

Bob,

You are quite literally "pissing in the wind" here. You really do need a set of PEMs in the LH and EZ pooters, a wideband O2 kit such as the Innovate I use and access to ST2 or better still ownership of one if the finance minister allows. I presume you have a stock MAF and not a super MAF? Mixing them up would create quite some confusion- I doubt that is the case but...?

Indeed you may do well to bin the adjustable fuel pressure regulator and stick with a stock unit as well- anything infinitely adjustable has one correct setting and as you now know, an infinite number minus one wrong ones!

Once you have the correct fuel pressure, ST2 can download the std tuning programme for the 928 and when you tell it you have 30lb injectors it wil automatically adjust to compensate. That would probably get you going and you can then tune to your hearts content. If Bill were close by I am sure he would give you a hand.

Whether or not something else is going on is a bit difficult to say- if the new MAF worked ok in another car for sure that is not the problem. If another MAF works in your car that is confusing.

Regards

Fred

AO

This can be caused by a number of issues, and not just the MAF. From your trial and error, it sounds like the MAF is NOT the issue. Other items to consider include: Temp 2 sensor, Throttle Position Switch, CPS (as previously noted), O2 sensor, LH, Fuel pressure regulator/Damper, Injectors, etc...

With the modified engine that you have, you should have a WBO2 sensor (if not... ). What does the WB tell you at idle? Sounds like it's going very rich.

SeanR

As Andrew said. Something as simple as a Temp II sensor boot folded over with exposed wires could cause this.

jcorenman

If I understand Bob correctly, the car runs fine with Bill's old/spare MAF. That means the temp-ii, CPS, injectors, framistat and picolyzer are all working correctly.

This is a tuning issue, and the MAF is definitely part of the equation-- not because the new MAF is out-of-spec, but because it isn't. Fred said it best-- without Sharktuner (or at least a WBO2) we're literally stumbling through very dark caves without a flashlight.

This is a 6L engine with non-stock injectors, adjustable fuel regulator (originally set to lower pressure), tuned years ago maybe with a Sharktuner or maybe not, with a MAF that might be the old one or may be a predecessor.

It is quite easy to go down the rabbit-hole of tuning an engine with an old worn-out MAF then swapping MAF's and finding the engine too rich to run properly. This is because the maps get "centered" on a MAF that reads stupid-lean, so it doesn't have enough range to accommodate a newly-rebuilt MAF. With an old MAF the LH should be adding fuel like mad with its adaptation, and not centered. Porsche got it right with the original maps, but this isn't an original engine.

It sounds like it runs OK with Bill's old/spare MAF, that's likely because it is a better match for whatever the engine was originally tuned for.

So the choices are either:
(a) Get the engine back to the same configuration it was tuned with (e.g. reduced fuel pressure, an older MAF) or
(b) get a Sharktuner and tune it properly, or hire someone who can.

At a minimum get a WBO2 on it and confirm that it is overly-rich with the new MAF. That will also provide some guidance on which way to adjust the fuel pressure, but the problem with that sort of "tuning" is that it only optimizes it at one point-- e.g. idle-- and it will still be messed up everywhere else.

RET

Thanks for the replies.

Fred is likely correct: I am definitely flailing about and I should just do the logical thing and Shark Tune it, particularly since I have no idea what fuel pressure was used for the original tune by Devek, but I know that the car was tuned with a lowered fuel pressure and that it used to idle correctly and I would like to resolve the problem, whatever it is, before adding complications.

If merely lowering the fuel pressure causes the engine to idle happily, then I will have to consider Shark tuning since I have no idea what the original setting was, otherwise I will continue to try to find out what is wrong.

I assume that the rebuilt MAF is causing a too rich mixture at idle, if not throughout the RPM range. This is based on the facts that two old MAFs, one of which was reported by Louie Ott to cause lean running, and the other one definitely old, abused, and of unknown provenance, allowed the car to run seemingly well and idle properly, while the rebuilt MAF runs and idles well in Bill's car, but causes mine to stall at idle.

Also assumed for the present, is that the other sensors are working properly. FWIW, all of the sensors tested OK at the LH and EZK connectors, per the 928 test specification, except the cam Hall sensor (and I am not certain that the test method described for it was valid...). The tempII sensor is new and the O2 sensor has less than 15K since new.

What wide band O2 sensor is recommended?

Thanks,

Bob

AO

Just stop for a second and back up....

Why did you replace/rebuild the MAF in the first place? There is a piece of information here that is missing.

You are assuming the MAF is the culprit, but maybe it's not. The fact that one of Bill's MAFs works/ new one doesn't... blah blah blah. is not statistically valid, it's just anecdotally accurate. THis is what prompted question above about why the MAF was replaced to begin with.

Do not assume anything at this point. You really just don't know until you check them off the list. (A sharktuner and WBO2 makes quick work of a lot of this.)

As for WBO2 sensors, get one. I like the Innovate. There are others out there - do your research. You will want to run it independently (i.e. do not replace the NBO2 on the car).

Once you know what's happening (too rich, too lean, etc.) then you can begin to rule some things out, or consider other things to check. Until then, I think you're just pissing into the wind.

FredR

Bob,

I use one of the earlier Innovate kits but there are others out there like the Aussie Tech Edge if it is still made. The WBO2 kit on its own for sure is helpful but it is not close to the insights you get with ST2 and Jim's Sharkplotter programme that even half wits like me can use.

The adjustable FPR had its uses in years gone by when there was no sharktuner but for custom creations like yours one really needs some kind of meaningful analytical tool. A stock FPR will eliminate a source of infinite variation. With the autotune feature in ST2 you can have the cruise map running nicely in about half an hour. For full load tuning one really needs a dyno or a brave co-pilot.

Rgds

Fred

UKKid35

Option (c)

Ask Bill whether a freshly rebuilt MAF is worth more to him than his old spare MAF that is probably out of spec.

Lizard928

This is terrible advice. Bills old MAF will age more and he will be back at the same issue.

But a set of PEMS, a innovate Digital MTX-L and then have a knowledgeable person with a ST2 tune the car.
This is the only way to properly fix this car.

I would recommend ditching the adj FPR and put a stock on back in there.

UKKid35

Fair enough Colin - That's difference between me and someone who knows what they're doing!

However it is worth having options that don't involve massive expense, even if they're far from ideal.

RET

Andrew – My methodology might be inefficient, but I am trying to isolate the problem.... As stated previously, the listed sensors, etc., seem OK. The original MAF was replaced because it caused lean running during warm-up: engine would start fine with higher idle when cold, then would settle down to normal idle as it warmed, but no power until the engine warmed (although it ran smoothly). It ran as if it had a carburetor with a faulty automatic choke and also seemed down on power. Bill's MAF seemed to clear all of the evident problems (we even swapped in his LH and EZK to no effect), and Louie Ott tested the old MAF and said that it would cause lean running. I am certain that the original tune was done with a lowered fuel pressure. Unfortunately, I have no idea what that pressure might have been. Marc Thomas has not responded to my messages, and of course, he might not have known, or might not remember, anyway....

Latest experiment: Started engine with Bill's MAF (which is old and I assume causes lean running also...); idled and drove well; stopped engine, reduced fuel pressure to 40 psi; installed the new MAF and started the engine. It idled a little raggedly at first, but maintained RPM and did not instantly stall as it did at higher pressures, but I was not about to drive it this way...

I have to conclude that the problem is fuel pressure, and have no desire to try to figure this out by trial and error....

Sorry for my ignorance, but what needs to be done to the car to make it Shark Tuner compliant?

Thanks again!

Bob

FredR

The LH and EZ computers need to have PEMS installed instead of the current EEPROMS. You need a WB02 kit, you need access to ST2 [or acquire one] with the correct interface adapter [round or square one]. You should also fit a stock FPR.

Thats about it I think.