#4 alt - voltage problem

[crazygn]

the last two days now my car has been bake firing at half thottle. I checked my voltage today and it was 11.5-6volts with the car running, this was at the batt and alt. So i checked my ground and had one real lose[ thought it was it] but now its 12.4 volts with the car running and still back firing when under boost, but my voltage light is not on.

I dont get it should 12v be good to run the car , seems like its to low to keep it firing under boost. plus iam getting the same thing at the alt and batt so maybe my 3rd alt is broke now to.


any idea's

 

[cool 84]

12V isn't enough. The car will backfire under boost. In my experience 13V and under is asking for trouble. On top of the ignition, a 1V drop has a huge effect on fuel pump performance.

One suggestion, I went through 4 alternators in less than 6 months. It happened to be after I went from the stock uppipe and headers to aftermarket headers and uppipe/DP. I figured out that the alternator sucks air through the back, right in front of the headers/uppipe which was now unwrapped vs the stock wrapped one. I wrapped the pipe and never had the problem again, I've had the same alternator for a few years.

It's funny your volt light isn't on. If the light is burned out it won't charge. If the single wire coming off the alternator going to the light has a problem it won't charge or won't charge enough.

 

[6SENSE]

I think what would be important here is to see what the voltage actually is under boost? Do you have a Scanmaster or TLink so you could see what the voltage is doing under acceleration? Also, if youve got a FP gauge that you can look at while driving, watch your fuel pressure and make sure its climbing with your boost (if worried about what the pump is doing).
I had a under boost backfiring problem a while back. Wound up being a bad plug wire on the passenger side.

Also, heres a vote for exhaust wrap on the aftermarket upipe (and at least the upper portion of the DP for that matter).

 

[crazygn]

Never thought of that being the problem , but i know the alt gets smoking hot next to the up pipe so maybe i'll try that. I have a tlink but the cable is being sent to be looked at and i could not see my fuel gauge last night on the windsheild. at 11 volts the volt light would come on but at 12 volts its not , crazy.

thanks guys

 

[cool 84]

I'll bet money the wrap solves the problem. I was very surprised the first time I figured out the alternator sucks air from the back and blows it out through the front. Seems like they would last much longer on the hotair cars if the airflow was reversed.

 

[crazygn]

well it looks like time to get some wrap and a new alt .

thanks man