Car falls flat on it's face at 4,200 rpm

[badstang123]

I got the alternator today and put it back in. I decided to switch to all stock pulleys because I think I was overspinning the alt with the smaller pulley on it. Everything seems to be fine. I wish it put out a little more amperage on idle but there isn't too much I can do.

If I mess with that screw on the throttle body that links to the IAC will it raise the idle for good or will the computer adjust it back down? Thanks
- Justin

 

[HISSIN50]

If I mess with that screw on the throttle body that links to the IAC will it raise the idle for good or will the computer adjust it back down? Thanks
- Justin

It depends upon how the idle was set. My preference is to set the hot idle with the IAC disconnected. If you did it this way, you can turn that screw/shank to raise the idle manually.

If the idle was set another way (some people use a method of setting the cold idle) then the IAC might be able to play around with any adjustments.

There is a bleed screw on the IAC that can be used to raise the idle. Note that this is a controlled vacuum leak and if the screw is loosened too far, it can create vac-leak-like symptoms (hanging idle, etc).

For many alternators, if you get idle RPMs to about 750 or a hair more, the output with a load is alright. I've also had to fine tune my idle just to accomodate electrical load.

Good luck.

 

[badstang123]

So you just make sure the car is up to operating temperature, then disconnect the plug on the IAC while the car is running, and finally tune accordingly?

 

[HISSIN50]

So you just make sure the car is up to operating temperature, then disconnect the plug on the IAC while the car is running, and finally tune accordingly?

If you like to fart around with things, you can do this. The simple answer is to just raise the idle up without disconnecting the IAC and see how it does. I mostly posted the other stuff in case you knew how the idle had been set before (the cold idle setting procedure is very popular on here - I just personally dont use it).
If it turns out that this simple adjustment doesnt work (your IAC is being utilized for the hot idle now, so adjusting the stop makes the puter close the duty cycle on the IAC and lower the idle), you can disco' the IAC and set it that way (so the computer cant lower the idle after you set it).

I like to record all idle adjustments so I know where I am relative to where I started - you can always go back to where you are now.

Wow, that post is clear as mud.

 

[badstang123]

Wow, that post is clear as mud.

Lol...I think I picked up most of what you said. A while back I tried to adjust that valve to get the idle up a bit. I did by turning it off and adjusting that screw and then restarting it. After a week the computer seem to adjust the idle back down though. I'll try it like you said and see what happens. I know I just need a small bump in idle speed to get the alt putting out what I need. Thanks for you help.
- Justin



Edit: By the way, the car still falls on it's face at higher rpms after all of that. The point is a bit higher, but I'm still having the same problem of voltage falling off. I have a friend with a stock alt I'm going to try and switch in there. If that fixes the problem I'm going to tell the guy who built my alt to shove it and give me my money back.

 

[S351R"Animal"]

If your mass air meter goes bad it will do this.

 

[badstang123]

If your mass air meter goes bad it will do this.

It could make it miss at high rpm or it could cause the car's voltage to drop from around 14V to 12V? I'm sure that this voltage drop at high rpm is related to the power problem because it would affect spark, fuel delivery and I'm sure some other things too.

 

[HISSIN50]

I cant even remember what's going on in this thread, but I wouldnt necessarily relate a voltage drop to loss of performance. Remember that track cars often run with no alternator - you know if anything was being left on the table, it would be WELL worth the tiny parasitic loss of driving an alt to get a tiny bit more power.
If you drop to 12 volts, that's just a tiny bit of discharging. And unless you're at the limits of fuel pump delivery or something, the lack of 2 volts wont matter a ton. Remember that many computer controlled systems use a VREF of 5 volts to help with such voltage fluctuations.

I say this only to try and isolate issue(s).

Good luck.

 

[badstang123]

In that case, I have an extra coil, mass air sensor, and Air charge temp sensor. I think those would be the first things to try swapping out.

 

[badstang123]

I was getting on the freeway yesterday and some guy in a semi was trying to wish death upon me. I floored it to pass him while getting merging and the alt blew up again (Thank god I made it home before the battery was completely dead). Both times now it stopped working when I took the car near redline You think they just built this thing bad, or is something in my car causing a problem only at high rpms. I just can't imagine anything electrical in the car that could downright kill an alternator like that.

 

[gcomfx.com]

Put a stock one on.... if it's your car you should be able to pop that sucker quick. I'm betting it's the place you are getting your BIG fancy alts from though.

 

[badstang123]

False alarm. I was so pist when I barely made it home I didn't even look at it until today. When I went to pull it off I noticed the connector holding my 1/0 awg wire on broke. Thus nothing connecting the alt and batteries. Thank god it was an easy fix and not the alt again Also thank god I didn't get a fire or something under the hood