AGP crew what is your take on the big turbo stumbles? - SRT Forums

Ultimateone · 06-14-2006, 10:18 AM

Lean Spike/ Stumble after Return Line Install? Numerous Cases?

What FP do you recommend? What line should we use, the nipple on the cold pipe? Should we use a check valve? Does sparkplug gap truely matter?

Jon@AGP · 06-14-2006, 11:21 AM

I fail to see how installing a larger turbo will cause any kind of stumbling. Your fuel modifications can have an effect on how the car runs though, especially if not installed correctly.

The RC injectors do not like to open at very low fuel pressure. If you have a return line, I suggest starting off at about 42psi of base pressure. If your fuel pressure regulator is seeing vacuum at idle, it is possible that you may be seeing too low fuel pressure which can cause stumbles and some idling issues. I suggest running a boost only source (T'ing the line going off the compressor housing works) to the regulator instead if you are experiencing problems. This will still increase the fuel pressure for every pound of boost you are running, but will not lower the fuel pressure very much below your base pressure at idle.

For plugs, there are so many different kinds of plugs that are available that people are running. NGK does not make a direct replacement plug for the SRT4. Depending on what kind of plug you are running your gap will vary with someone who is running a different kind of spark plug, so it is hard to give a suggestion since what works for one type of plug may not work with a different plug.

Nick@AGP · 06-14-2006, 11:31 AM

To follow up what Jon said, yes spark plug gap matters. It can make a huge difference.

Ultimateone · 06-14-2006, 03:47 PM

Thanks Jon, Im not saying because we have big turbo's we have problems its just that 90% of the people experiencing the problem do have turbo upgrades.

Also what if I dont have a nipple on the compressor? I do not so this is why Im running of the cold pipe, can I T off the TB with a check valve?

Thanks again for replying

Quote: Originally Posted by Jon@AGP

I fail to see how installing a larger turbo will cause any kind of stumbling. Your fuel modifications can have an effect on how the car runs though, especially if not installed correctly.

The RC injectors do not like to open at very low fuel pressure. If you have a return line, I suggest starting off at about 42psi of base pressure. If your fuel pressure regulator is seeing vacuum at idle, it is possible that you may be seeing too low fuel pressure which can cause stumbles and some idling issues. I suggest running a boost only source (T'ing the line going off the compressor housing works) to the regulator instead if you are experiencing problems. This will still increase the fuel pressure for every pound of boost you are running, but will not lower the fuel pressure very much below your base pressure at idle.

Ghowie · 06-14-2006, 06:40 PM

you don't have a nipple on your turbo? where's your wg line running to then?

Ultimateone · 06-14-2006, 07:04 PM

Im/tb.

jhempstead · 06-14-2006, 10:06 PM

In my case and other srt's around here, it is a big injector + low fuel pressure problem. Just as the agp guys said, you need to make sure you have over 40 psi @ idle. If your rrfpr sees vacuum, it will lower the fuel pressure by ~ 5-10 psi, causing a stumble. So do what you have to do to get your fuel pressure over 40 psi @ idle and your stumble will go away.

mihimahi · 06-14-2006, 11:54 PM

So, about what Jon and Nick have both said about the FP and Spark Plug gap:

Give us a basic starting point.

Lets say with your guys' 50 trim and a fuel return line:
with vacuum at idle: 42lbs?
****or**** WITHOUT vacuum at idle: 42 lbs?

Also on the plug gaps... I have your guys' AGP7 plug set. I have them gapped at .35 for daily driving.

Any suggestions, or does this sound ok?

Ultimateone · 06-15-2006, 05:50 AM

I think Im gonna put a check valve on the FP line.

mihimahi · 06-15-2006, 11:01 AM

Quote: Originally Posted by Ultimateone

I think Im gonna put a check valve on the FP line.

I own a Pet/Tropical Fish Center, and the check valves I can get are all tapered on the ends, so it makes it hard to attatch them solid with small zip ties... however I did it and it does work. Then someone suggested I take it off. I would like some more expert ( AGP ) opinions.

So, should we be using a check valve on the FP line and adjust the FP to 42 or so without vacuum at idle?

aaronneon@RealTune · 06-15-2006, 11:08 AM

I cant believe you guys are still having these problems after everything we have went through in the other thread.

Are you not tuning the problem out, or are you looking for a one thing solves all idea. Thats just not the case. you need to do EVERYTHING we listed off months ago.

raven · 06-15-2006, 11:53 AM

Quote: Originally Posted by aaronneon@RealTune

I cant believe you guys are still having these problems after everything we have went through in the other thread.

Are you not tuning the problem out, or are you looking for a one thing solves all idea. Thats just not the case. you need to do EVERYTHING we listed off months ago.

Go kick his ass aaron.

aaronneon@RealTune · 06-15-2006, 11:57 AM

Quote: Originally Posted by raven

Quote: Originally Posted by aaronneon@RealTune

I cant believe you guys are still having these problems after everything we have went through in the other thread.

Are you not tuning the problem out, or are you looking for a one thing solves all idea. Thats just not the case. you need to do EVERYTHING we listed off months ago.

Go kick his ass aaron.

LOL. Its not like that. I just dont get it. We walked everyone through the steps.

-ND4SPD- · 06-15-2006, 11:59 AM

I know this seams like it sould be easy to fix but it's been everything but that. I've spoke with Aaron, Vector, Several people at AGP, several people at DCR, Some people at 3Rracing.... which everyone's offered alot of good advice & direction. Unfortunately I'm still battling this as many other's are too.

I have been to the Dyno 3 times in the past 6 weeks & have tried EVERYTHING that everyone has mentioned. I've tried every combination of those things together as well. I even tested out a few of my own theory's.

I re-wired my SAFC, I switched to smaller injectors, I re-did all my vacuum lines, I tightened all my fuel lines, I tried everyone's suggested SAFC settings, I tightened down every bolt on the turbo, I did a boost leak check, compression check, changed fuilds, changed plugs & tried a few different gaps. NOTHING has fixed this problme other than 52+ psi static FP.

My next line of attack is going to be swapping out the SAFC for D-Tec & doing the bottleneck fix (I'll verify that the fuel pump is installed correctly as well). I'll also be hooking up my FP gauge inside the car so I can watch what it's doing.

Here's a quick comparison.

aaronneon@RealTune · 06-15-2006, 12:02 PM

What Im saying is not one thing will fix it. In your case, I would bet there are a few things harry there. Just looking at the a/f and you can tell that.