Hey all,

I've been running pretty much the same tune for about 6 months, but have recently noticed a problem. This problem is most noticeable in third gear, cruising at 4000 rpm's, if I go WOT at 4k. The car will hiccup a couple times between 4000-5000 rpm's. It seems to coincide with peak boost.

The way to describe it is:
-at 4k, go WOT, car starts to pull, then hiccups, then pulls, then hiccups again, then pulls the rest of the way.

When I looked at my log, the timing and boost profile looked ok (although peak boost was higher than I expected by about 1 psi). However, I noticed that I have a couple of places in the log where th RPM drops by 15-30 rpm's, then picks up again. I wonder if this is the hiccuping I'm feeling.

With this RPM drop, could it be tune related? Or would it be due to a bad factory clutch? I have less than 15k miles on the car, so I'm hoping it's not the clutch. Also, I'm running a tephraXMOD ROM, so when I use the alt-map which is the stock map, I don't notice the hiccuping (which could be due to either the stock tune or less power). Thanks for any suggestions!

Note: I also get a similar problem in lower gears going WOT at about 3k rpm's, but it's just easier to replicate in third gear at 4k.

 

Do you have the blue fuel pump relay?

Have you checked the fuel pressure regulator vacuum hose? (it's the one by the dip stick, just under the engine cover.)

 

Yup, replaced all three black relays with blue, plus the MFI relay with the new gray one. Also did check the FP regulator vacuum hose.

To me, this seems either power or tune related (since switching to stock map doesn't have this problem). Could a tune problem cause RPM to drop slightly during a WOT pull? Or is it a mechanical problem? From my logs, I can't seem to identify anything majorly wrong with timing/boost.

 

What year is your car? Sometimes it happens if you are too rich or lean during spool. 2010's have lean spool.

 

2008 GSR, running TephraXMOD 52681022. Was previously using 52680018, but I did log wideband AFR when I first switched over about a month ago and AFR's looked ok.

Is it worth reinstalling the wideband and logging this, or should I maybe lower passive WGDC a little and see if that helps? I wonder if I'm now boosting too much since I'm at high elevation (over 5000 feet).

 

If it was running fine before what i would try and do is replace your spark plugs and gap them to .022 .

I see this all the time with Evo's .

 

OMG I am an idiot!! But thanks to Golden and 02-Lancer-ES. It was the stupid FPR hose!!! Golden, I was looking at the wrong end of the hose (I had only zip-tied one end). 02-Lancer-ES, I went out to check the spark plugs, and noticed the problem. So thanks again to both of you!!

Now the bad part - I've been doing quite a few WOT pulls to try to debug this problem, and also autocrossed the car like this. I've been driving around for 3 weeks this way... Could I have damaged something? I didn't have my wideband in, but do have tephra's knockCEL - most of the time I didn't get knock, even though the car was presumably running VERY lean Anything else I should check?