driveability/bucking problem

[mk2 supra]

Just getting my supra on the road for the first time. Im leaning towards MAF but Id like to know for sure. Heres the deal- It idles fine, light throttle is ok, but anything close to 0 psi and above the car gets a violent bucking going on. Power, not, literally like you were stabbing the gas over and over. In first gear its enough to chirp the tires. It blows no smoke during this, is on all the cylinders evenly, Ive flushed my whole fuel system so its not fuel flow. I show no engine codes. It had a code 31 as I was first getting the car running, I took the maf out sprayed it with maf cleaner and it went away. Pretty much everything is new on this engine so its not plugs wires ect. Ive done the ohm checks on the connectors of the maf, they looked okay, but I could be wrong the meter I was using wasnt ideal. Engine is an 88 7mgte, stock except turboback catless, intake, ect

 

[supraguy@aol]

You sprayed the maf with cleaner?
From what I've read over the past ten years, that's no bueno. The actual metering mechanism inside is somewhat optical, utilizing a mirror arrangement.
Do you have another MAF you can try?

 

[mk2 supra]

You're describing a karman vortex type. I know u can't clean those but I thought this was a different type but could be wrong. No I don't have another to try

 

[IndigoMKII]

Our MAF's can't be cleaned. They're karman vortex.

 

[mk2 supra]

Our MAF's can't be cleaned. They're karman vortex.

oh well that one sucked anyways lol. thanks

^ This. And check for codes first.
QUOTE]
you should read the post sir, but thank you. and I dont have the fuel pump resistor hooked up, its 12v all the time.
So nobody can tell me with the info that its actually the MAF thats bad tho? Or what to check? Ive read igniters can do a similar bucking but that would also include black smoke wouldnt it?

 

[IndigoMKII]

Bucking could be caused by.. Dirty MAF or improperly adjusted TPS(ECU thinks the throttle is closed but you're trying to accelerate) or loose transmission/engine mounts or driveline slack etc etc..

 

[mk2 supra]

Well its all throttle levels, its directly related to load/airflow. Lower rpms I can get away with a couple psi boost, higher the rpm the less it'll wanna do... guess its gotta me maf

 

[IndigoMKII]

Have you done a boost leak test at all? I know when there was a hole punched in my IC inside the fins, my car would buck like crazy anytime it hit boost.

 

[mk2 supra]

No I haven't... Ive been meaning to I have a tester from my dsm. This thing bucks at 0 and not one lb of boost so I haven't really suspected it, but ya ill have to check

 

[mk2 supra]

I unplugged the maf and tripped it into limp in mode. It still cuts out exactly the same. Does this rule out the maf? Also it wont go past 3800 RPM in neutral (free rev) if this helps

 

[jetjock]

I don't get it. Instead of guessing why not troubleshoot the problem properly?

 

[mk2 supra]

I don't get it. Instead of guessing why not troubleshoot the problem properly?

and the vauge post award goes to....come on man if I knew exactly what to check I would be doing it and not posting. Im posting what I HAVE been checking to try and rule things out and narrow down whats wrong. TSRM says to ohm test the pins on the maf plug, which I did and they check out ok, so I feel Im kinda winging it after that. Normally I would just hook up a datalogger and see whats logging but we obviously dont get that luxury here so thats why Im asking for help.
Last night I hooked up a fuel pressure gauge, Im all good there, it rises with manifold pressure, and doesnt drop with the bucking condition. I also motorvac'd the fuel rail just in case my injectors were clogged in the last 20 miles from bad fuel. It didnt help, but when I spray fluid into the intake mani it does wake up from the stumble so IT IS for sure a lean condition...
Could it be CPS signal?

 

[jetjock]

...Could it be CPS signal?...

No. Hope that's less vague...

 

[IndigoMKII]

Try monitoring your VF signal while driving it, what is it doing?

 

[Poodles]

For starters, we don't have a MAF, we have a AFM. Two completely different ways of metering air so it's important.

Also, have you checked for codes?

 

[xricer]

....Did you make sure there are no air intake leaks after the afm? I think if there is air getting in..ie, a cracked boot it will cause that problem? Or loose clamps?

 

[IndigoMKII]

For starters, we don't have a MAF, we have a AFM. Two completely different ways of metering air so it's important.

Also, have you checked for codes?

Forgive me but calling it MAF and AFM are basically the same. Now if I was to call the MAF a hot wire sensor instead of the correct, karman vortex sensor, I could see a room for correction but maybe you know something I don't.

 

[3p141592654]

He knows that a MAF measure mass air flow (grams/s) and an AFM measures air flow velocity (L/s).

 

[IndigoMKII]

I didn't realize there was a difference between MAF to AFM other than the sensor type inside it.

 

[jetjock]

Forgive me but calling it MAF and AFM are basically the same. Now if I was to call the MAF a hot wire sensor instead of the correct, karman vortex sensor, I could see a room for correction but maybe you know something I don't.

What 3p said. The ECU takes IAT and does the math. Anyway, now you know something you didn't. At least you were open to the possibility. Some who come here aren't.