[speedysprocket]

So I've been driving pretty reasonably for a while, now, but last weekend I opened her up from a stop light and the engine fell on its face.  WOT from low RPMs in first or second results in bad hesitation/stumbling.  Less than WOT is ok.  I've been having a little issue when I leave for work in the morning, I get to third gear by the first turn out of my neighborhood, and when I let off the gas (still in 3rd gear), the engine bucks.  So after I found this stop light problem, I thought TPS.  Changed that and no better.  I clean the MAF periodically.  Plugs, wires, cap, rotor all in good shape.  O2 sensor has maybe 12k miles on it.  Hall sensor was new when I rebuilt the engine 12k or 13k ago.  What else should I look at?  DME engine temp sensor? 

Thanks, Alex

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[94SilverCab]

DME Relay? That seems to be the bugger on all fuel/air related problems...

 

Jay

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[flash]

i'd be looking for a disconnected vacuum hose, like the ported vacuum hose at the top of the throttle body

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[williamoss]

Can anyone translate

 

WOT

 

TPS

 

MAF

 

please.

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[speedysprocket]

Vacuum lines are all good.  The only thing the ported one on the throttle body does anyways is open the valve for the charcoal canister.

Vacuum at idle is 20"Hg, highway off throttle goes as high as 25"Hg, cruise on the highway about 15-16"Hg...

Can anyone translate

 

WOT

 

TPS

 

MAF

 

please.

Wide Open Throttle

Throttle Position Sensor

Mass Air Flow (meter)

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[MLB]

Besides the forum search feature, I just found Google 'define' also does a good job of translating those TLAs (three letter acronyms):

Google: "define tps automotive"

Google: "define wot automotive"

Google: "define MAF automotive"

Top result each time

Just sayin'

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[94SilverCab]

That's a great tool, since we can't search on 3 letters here...

 

Jay

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[MLB]

Hmm, the forum search worked for me, for WOT

top result was the thread "WOT stumbling" which defined the term

For the other 2, being familiar with the forum categories is very helpful. A quick perusal of thread topics under Engine Management revealed one with "throttle position switch" in the title, which caught my eye. And several with MAF in the title, that defined the term during discussion.

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[speedysprocket]

Ok... and back to my issue at hand...?

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[blue968]

Just a thought, have you checked fuel pressure? Try hooking up pressure gauge and go for a ride and see if pressure drops when it starts to stumble. Fuel filter clogged or pump failing.

 

Good luck

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[speedysprocket]

Well put some Techron in last night and already felt better this morning.  I'll order a fuel filter and plan to send my injectors off to the Witch Hunter the next time I have to go out of town...

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[speedysprocket]

Well had my injectors rebuilt and changed the fuel filter and plug wires.  Feels as bad, if not worse now.  I'll try to check fuel pressure this afternoon, but what else could cause this?  It seems anything over 1/2 throttle in first or second below 3000 RPM causes this awful stumbling.

Also, are the 968 fuel rail hoses known for failing like the 944s, or are the original ones fine to leave on there if there's no visible damage?

Thanks...

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[flash]

have you changed the filter?  those things only last 60k

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[Waylander]

could be the FPR (Fuel Pressure Regulator) pull the vac hose off and see if is wet inside with fuel

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[speedysprocket]

have you changed the filter?  those things only last 60k

Changed fuel filter, drove car around the block, pulled injectors and mailed them to Marren.  Reinstalled injectors and still not good.

 

Just checked fuel pressure.  52 psi at idle, 60 when I open the throttle (or disconnect the vacuum line from the FPR).


What can I check next?

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[flash]

ok - fuel system seems ok.

 

sounds like a sensor/computer thing

 

your vacuum readings are high.  that tells me you are running lean.  this could be due to a sensor or a chip.

 

is the chip stock?

 

is there anybody around that could swap MAFs with you for a few minutes?

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[speedysprocket]

No, not the stock chip.  I can't remember the name off hand, but it's the one you said was pretty good except for the fact it makes the check engine light come on.

If I hook up my check engine light, should I be able to read a code?

And not sure about being lean everywhere- I only get 22-23 mpg...

Not sure about the MAF either.  I know there are 968s here, but I don't know any of them.

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[flash]

lol - well, i would start with getting that out of there and seeing what a stock chip does.  i doubt i would have said it was "pretty good" if it threw a light.

 

running lean can actually REDUCE your fuel economy, because it means you have to stand on the pedal more to get where you want to go.

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[speedysprocket]

I'll swap it and see.  It's the ProMax chip that's in there...

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[flash]

yeah - that chip runs lean in some areas to begin with.  if there is something else also going on, it would only exacerbate the issue.  for example, if you had an aftermarket exhaust, deleted the cat, or had the airbox mod, it would run even leaner.

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