AO

I just checked it against my GT's Temp 2 and they were virtually the same. I will try and swap the MAF with one I've not tried yet in this car to see what, if any changes, occur.

The only other thing I can think of is the WBO2 is goofy. I have a spare sensor, so I may swap that out too.

If these last two things don't uncover anything, I'll ST it and be done.

GregBBRD

Shark tuning on an '85/'86.....not my favorite task.

Great that it is possible (thank you, John), but fairly cumbersome.

AO

Agreed, hence my last resort.

mark kibort

id find the problem before I would engage in custom tuning!

AO

What do you think I've been trying to do? Circle jerk?

But at what point do you cut bait?

There are only a few things that may account for it. I've ruled out most. I only have the MAF, my WBO2 sensor, fuel pump, and injectors left to consider - in that order.

I really doubt it's the fuel pump after thinking things through, And it's unlikely the injectors are to blame, but you never know. I'm busy tonight, so unfortunately nothing will happen until Thursday after work at the earliest.

Action plan is as follows:

1. Swap with 3rd MAF. Measure results. If no change, move to step two. If it's all better, crack a beer and celebrate. Norm's Ragged-***!

2. Swap WBO2 sensor to see if in agreement. If yes, move to step 3. If reading now look correct, bash head against wall, grab beer to ice down bump, then drink. Sierra Nevada Torpedo sounds about right.

3. Hook up GoPro and go for a drive to see if FP drops off (unlikely). If it check out as good, move to step 4. If FP is the issue, swap in new FP, test again. If fixed, crack open beer. Bell's Two Hearted.

4. Pull spark plugs and read the tea leaves. If all plugs look the same, Shark Tune the MFer! If there are a few that are off, identify and swap in some different injectors to see if problem goes away. If it does, bask in the glory of all that is holy and drink copious amounts of beer. Smutty Nose Kindest Find sounds good.

If I have to Shark Tune... well then it must be something that is different about this motor. WHo knows... who cares. Just get the bitch running so you can make Mid-Ohio or Grattan one last time this year!

mark kibort

what AF meter are you using? what O2 sensor are you using. you said "wbO2 "sensor, but is that also powering the 928 LHsystem? or do you have two..one that checks AF readings and the other that drives the closed loop system. check that meter too... when o2 is not running the system, see what voltage you get out of the WB02 ... see if it matches the fuel mixture vs voltage known scale.
the o2 sensor might be bad and then gives you a bad reading? it might be fine and you dont know it. no pinging, plugs look ok, that might indicate that you are ok. best thing is to get another o2 sensor and try that.. also try having the o2 sensor disconnedcted but stilll connected to the AFR meter. if you do that now, what happens? you said it runs rough when the o2 is disconnected at the plug connection. (but hopefully its still connected to the AFR meter, ground and power) (thats key!)
could be your LHjet box. if it was the fuel pump, you would see fuel pressure that is not in the 40 psi range.

do the jack up and floor it iin 4th gear.. you dont need go pro and all you need is someone to witness the fuel pressure go down or up. or check your AF ratio via that meter when doing some changes. if you have a major issue, you shark tune, you might be able to fix it, but if you are tuning with a bad AFR meter or o2 sensor, you can do more harm than good. your sucess is dependant on that o2 sensor being correct. under WOT, you are not pinging which makes me think you might be running ok mixtures and the meter or 02 sensor is off.

check that circuit. make sure when you remove the o2 sensor, that the AFR goes up to 12.5 or something richer than when idling around.

AO

I'm using an Innovate WBO2 with a Bosch sensor. Pretty robust. Most Dyno shops that I've visited use this. But the sensor could be bad, that's why I'll swap it with a different one. Some of the cheapo WBs suck *****. This one does not in my opinion.

The WBO2 is independent of the O2 loop, but when you go WOT on all 928 (except maybe the early ones) you are open loop - so there is no O2 correction. I know my WOT switch is working, so the lean issues must be a matter of air measurement is off (MAF), WBO2 is whacked, or fuel delivery (pump or injectors).

I believe it's the MAF, and there is evidence from other to point me that way. I know the engine was rebuilt by Abby, and that the heads were rebuilt too. I don't recall seeing anything about a change in the cams, but if there was, then that might make sense.

I have my action plan... plus beer list!

AO

Update:

I swapped MAFs and the AFRs were about the same. Because the exhaust was hot, I decided to check to see if the fuel pressure was there or not. I jacked up the rear and put it on jack stands. Opened the hood, fires it up, slipped it into 3rd gear, applied a little parking brake to give slight resistance, and saw at "cruise" I only had 35psi. When I hit the throttle it only went to maybe 40psi, and that was pretty brief.

So, now I'm thinking I have a weak fuel pump (or some other obstruction/restriction). Will be installing the new fuel pump tonight or tomorrow to see if that fixes things.

Stay tuned.

PorKen

Probably a blocked intake screen, less likely the filter, bad fuel pump, kinked/crushed fuel line, bad fuel hose, but, also check the FPR vacuum line is connected to manifold vacuum via the 7-way, not to ported vacuum?

#NotTheChip

AO

Yes... Not the chips!

Pretty sure the vacuum line is correct, but will double check.

I was thinking about the screen as well. Will try the pump first and inspect the lines in case someone jacked on them or if they were kinked in the accident. If still no change, will go for a new screen.

We're close... I can feel it.

mark kibort

not the screen.. that wouldnt do much. ive run them with and without with no difference. maybe more power without, but never dynoed, so it not probable that its the blocked screen. in fact, you can cover it with some old socks and the mixture will be the same. (ask me how i know )


if you are getting 40psi on a blip... did you WOT and see the pressure as i suggested? dont use the parking brake,, use the main brakes and have someone look at the gauge 4th gear and warm up to full throttle. that will determine the fuel pressure problem or no problem.

the vacuum lines is not the issue. you already saw an increase of fuel pressure on increase throttle, so its pulling back pressure at idle. 5psi is about right. 35 to 40psi as you saw.
did you swap fuel brains ? chip? thats my guess.

OTR18WHEELER

see post 17, you've checked everything else, but while you mention the o2 as a possibility, have you changed it out yet?.

mark kibort

or can you check the AFR with the 02 disconnected! that will be the first clue.... should be running richer just by that alone.. (part throttle, not WOT, where the O2 is not even used)

AO

Update:
I replaced the fuel pump last night. The old one seemed to be leaking slightly. I also swapped in the new wideband O2 sensor. I just took it out for a spin and the results are the same.

So I just jacked up the rear end again, and hooked up my camera so I could record the fuel pressure ra so I just jacked up the rear end again, and hooked up my camera so I could record the fuel pressure gauge. Did 2 pulls. Pressure seems t be stuck at 40psi.

http://youtu.be/UEDquWWg6cs



Double checked vacuum line routing, and the FPR comes off the multi connector.

So what's left? MAF? Fuel filter? Thats all I can think of.

AO

Oh... For you Mark.