Rough Idle after procharger install...Please help.

[Scott94C4]

Hi Guys. Hopefully someone can help me track this problem down. I had my procharger installed at a shop nearby along with 30# injectors and a walboro 255lph fuel pump. The shop also tuned the car and put in colder plugs. Now for the problem: After the car warms up (it idles fine when cold), the rpms at idle drop to about 300 then shoot up to 1200 and back down. It occasionally stalls. Here is the clencher: when I unplug the vacuum line to the surge/bypass valve, the car idles just fine. I have a boost and fuel pressure gauge installed and the fuel pressure is fine from what I can tell. Whenever the car's rpms surge the fuel pressure drops and increase with the RPM. Not sure if that is a sign or not. At any other rpm the car runs fine and is lots of fun. Also I am at 6200 ft above sea level (if that helps). The mechanics says that my surge/bypass valve is too small and not letting in enough air at idle to maintain it. I am not sure if that makes sense. Please help guys....

[krivera]

Scott,

What year of car do you have...what is done...what blower did you get, are you running an FMU..etc?

I had that same problem but really it is to early to tell if my fix would fix your issue but on my 91 (383ci, stock TPI, 30# injectors, stock fuel pump, ATI fuel booster, and stock bypass valves...)

But what was happening with my car was the fuel pressure reg was blown (diaphram inside) and it would not idle because it was leaking that little fuel and the ecm is trying to control it.

Let us know what you got and what you can try is pull the belt off the car and start it (dont let it over heat) and see how it idles without the blower.

[Brand-X]

I had a similar problem but not as bad what you are talking about...it was the maf sensor. relocated it to a blow thru configuration and cured my problem.

[AKS Racing]

I had a similar problem on my firsat ATI install, but mine was able to be cured with tuning. It was getting too much air for the amount of throttle opening. In a sense, the opposite of what your mechanic stated. All was fixed with tuning.

Aaron

[Bruce]

is this problem are only effect MAF?? Because my 93LT1 speed density I did not have any of that problem.


Bruce


[Modified by Bruce, 11:38 PM 1/9/2004]

[AKS Racing]

The problem I encountered was associated with the MAF, so I would expect that it would be related to the cars with MAF vs SD.

Aaron

[Scott94C4]

Wow, Thanks for all the replies guys.

To answer some questions: I drive a 94 LT1 corvette 6spd. P1SC blower, Yes I am running the FMU (wanted to ditch it, but mechanic installed it anyways (SO if anyone can give me some help on how I can drop the FMU and get it tuned that would be great).

The only problem I see is if I take off the belt and run the car, it only does it when the car is warmed up and by that time (with no water pump) will it overheat or will it die (because of no alternator)?

But I can give it a shot.

ALSO: with the MAF sensor, can someone tell me how to move it in detail? I assume you are talking about moving it inline after the blower (between blower and throttle body). If I do that will it damage the MAF (with the all the extra pressure through it)? Also, how or where did you get the intake piping to fit in the MAF sensor in a different area?

Thanks for all your helps guys. :D

EDIT: also can you guys think of why when the vacuum hose on the surge valve is unpluged the car idles fine?


[Modified by Scott94C4, 11:23 AM 1/10/2004]

[Bruce]

had a similar problem on my firsat ATI install, but mine was able to be cured with tuning. It was getting too much air for the amount of throttle opening. In a sense, the opposite of what your mechanic stated. All was fixed with tuning.
Aaron

[Brand-X]

I relocated my MAF to before the intercooler (no good place to mount it between the intercooler and throttlebody. Also, you'll need some 3"-to-4" rubber couplings (the MAF diameter is larger than the piping going to the intercooler)...you might want to measure the two pieces as it has been awhile since I converted--my bad memory!

Starting at the air filter, finishing at the throttlebody:

1.) Air filter
2.) Steel piece w/BOV return
3.) rubber connector
4.) 90 degree steel elbow
5.) rubber conector
6.) inlet boot
7.) blower
8.) 90 degree rubber elbow
9.) oval steel piece that goes over radiator shroud
10.) rubber connector
11.) steel piece w/bov port (must be cut down to ensure good hood clearance)
12.) 3"-4" rubber conector
13.) MAF
14.) 3"-4" rubber conector
15.) intercooler
16.) no changes to the rest of the tubing between intercooler ad throttlebody

The only problems I had with the blow thru setup was when I blew a seal in my blower and oil mist was causing my maf sensor to throw some weird voltages (caused car to surge while cruising...no problems at wot as it goes open loop).

Any diy turbo site can sell you the 3" to 4" tubing.

[Scott94C4]

Thanks Brand-X and everybody for your help. I will try to relocate the maf.

Thanks again guys.