dyroot

OK, so Ive been having a problem with my 87 pickup for a long time. Its been doing this thing where when you first start it up, for the first 30 seconds or so it runs and idles fine, then it wont go above 3k, and ever minute or so it goes down another 500 RPMS until the truck wont go above 1750. It runs real crappy when it gets up near those RPMS, and the mechanic said it was running way too lean. he said fuel flow was good so I assume that means pump is fine, and they replaced the fuel filter to try that as well. So, with the help from a few mechanics, they think that the MAF sensor is a possibility here. So If i unplugged it and ran the truck and saw that it worked fine without it, would that tell me it was the MAF? or is this bad for the truck, i dont plan on doing it very long, just long enough to see that it works. I heard this might work because the ecu goes into a default setting without the sensor there.
Thanks

iamsuperbleeder

No, on these Toyotas, if you unplug it, the truck just wont run, period It'll start up for a second, but it'll shut itself off. There's an internal mechanism in it that sences once the motor is running, and it keeps the fuel pump running. If you unplug it, the fuel pump will cut off just as soon as the truck starts.


It does sound like it could be the AFM, but the correct way to test it would be with a good multimeter.

Also, check to make sure it's not sticking. These are mechanical meters with a flapper door inside, and sometimes they can stick and cause all sorts of issues, but that usually only happens if you suck some water into the intake... you haven't sucked in any water lately, have you? :hillbilll:

abecedarian

You may be able to jumper the fuel pump on using the test connector. See 4Crawler's site for more information: http://www.4crawler.com/4x4/CheapTri...shtml#FuelPump

When you hit that upper limit on the RPM's do you get any backfiring or afterfiring?

Also make sure that there are no cracks in the intake duct and boots 'cause any air that gets into the engine without going through the AFM can make the fuel mixture lean out too much and you'll lose power and possibly damage the engine.

I would think that the ECU would recognize that the reading from the AFM is not correctly tracking the engine speed and throttle position and throw a trouble code / check engine light, but I could be wrong.

Finally, have you adjusted the timing at all? Have you checked the spark plugs, wires and coil?

dyroot

Thanks for the replies. What makes me think its the AFM is that it gets worse at different engine temperatures. I dont see any cracks or anything, but Ill further insepct that tommorow.
There is no codes put out because of an engine swap from the tubo engine to 22re something got messed up and not theres no diagnostic connector or CEL's (i know..lame)
Timing was just recently set, spark plugs, wires, ignition coil was all changed too recently.
It does backfire though sometimes...not all the time though, id say like 10% of the time when I rev it to the upper limit and keep flooring it, it will backfire.

dyroot

OK so i tested the AFM with a multimeter, but just a static test of the pins, just with the car off, and they all tested good. I didnt think it would be off at this part anyways though, cause it idles fine, its just when it gets throttle it hesitates at around 1800 RPMS once warmed up

myyota

Check the TPS, if its bad it can cause the problems your having.

dyroot

I tried running it today with the TPS unplugged, but it still did the exact same thing.
It idles fine. Once it warms up, it idles smoothly at around 900 RPMS, and the throttle is responsive up to about 1800, then it just starts surging. Say its add 1750 and i give it gas, it goes up to 1800, then even though my foot is still on the pedal, goes to about 800 for a second then shoots back up to 1800 and over and over again. any ideas?

dyroot

posted a video on youtube of the symtoms
http://www.youtube.com/watch?v=dHc4XTxYwGk
any ideas?