View Full Version : Performance issue, pre boost

09-24-2012, 05:07 AM
What could cause a motor to feel like its hitting fuel cut pre boost? When I get into boost its fine, but there is no power when trying to get there and as I open the throttle, it jerks my around almost as if I was hitting fuel cut.

If more info is needed, let me know. Just trying to get ideas for what to poke at. Plan on building a boost leak tester soon just to rule out air issues.

I bought this car non running and most things around the motor dismantled. I have put everything back to the best of my ability, but as I go through this car I am finding that there were things left installed that may have been tinkered with before me. So my knowledge of this car is as follows.

Bought 2 owners ago from someone in Idaho. Had a engine rebuild, but 2 owners ago thought it might have been poorly done.
1 owner ago dismantled alot under the hood. Had injectors cleaned. Never reassembled or said reason for dismantling, but did say head bolts werent tight and some other mechanical things I dont recall.
Me, I have reassembled and got her running with fresh gas. Checked everything visually during assembly, but no indepth checks.

Also, it revs fine. Just when trying to move it struggles and hoping to get the documentation on the rebuild this week.

09-24-2012, 05:11 AM
Ignition misfire, tuneup parts.

The Captain
09-24-2012, 02:52 PM
Could be that or air. At idle and really light, steady throttle the ECU looks mostly at the O2 sensor. Pretty much ignores the AFM. Outside of that it's the AFM/TPS etc. I'd take a good look at the AFM and TPS adjustment.

When my AFM went bad it ran like shit off boost except at light throttle but fine on boost.

09-24-2012, 05:45 PM
What cappy said. The TPS controls timing. Check your TPS, and your AFM. Possibly your O2 sensor.

09-24-2012, 09:23 PM
K. I will look through my BGB's and see how to tweak those and recheck my ignition. Hope it helps.

Would rather not have to replace any major electronics till I go standalone.

Thanks for the guidance.

09-27-2012, 03:15 AM
Where can I find steps for testing the AFM? The BGB I have has steps for testing the TPS, and I assume loosening the 2 screws is how I adjust it.

And to add to the issues, and also see if they could be related or just more for the pile. I am throwing a code 22 right away. Coolant sensor. Need to hit a junkyard if I dont have a spare.

Also, the idle is high the whole time. I turned the idle screw all the way down and got it to 1k. With the code 22, could that cause the ECU to stay in cold start?

10-01-2012, 03:03 AM
IMO the BEST way to check the AFM is to get an ANALOG multimeter [or voltmeter].
All you need is 0-5V DC.
Everything hooked up.
Hook up the pos lead to the VS pin at the ECU, neg can be grounded anywhere. Just make sure it's a good ground.
Drive the car around while watching the meter.
The signal should go from mid to high 4 volts and the more throttle you give the lower the voltage should go.
It should also move smoothly.
This will tell you if there's a break in the resistor. It won't tell if the spring is weak and not reading the right amount of air though.
And it's more accurate than with a digital meter or with a resistance check.

Bad ECT could cause a high idle.
And since you know you have something wrong, and you have a problem; the first step in troubleshooting is to fix any known problems. :)

10-01-2012, 03:38 AM
Bad ECT could cause a high idle.
And since you know you have something wrong, and you have a problem; the first step in troubleshooting is to fix any known problems. :)

Lol! Thanks. I figured as much. Figure the first on my plate is the ECT sensor and fuel filter. After that test amf and tps. HAvent dove too hard into the car in the last week due to being busy.

11-09-2012, 01:41 AM
Hey, alltracman, is the only way to test with the analog, or does it just make it easier then a digital?