my 05 s will at times hesitate or bog down when accelerating. problem seems more pronounced below 3500 rpm or so. seems ok above this rpm. it hasn't always done this so I think something is amiss.
Here is what I have done to troubleshoot:


Swapped plugs with a known good set of used plugs. no change. Plugs I took out looked fine. Slightly dark tan color and dry. All 4 looked identical.




Swapped aftermarket wires back to stock wires. no change.


Changed fuel filter. No change.


checked fuel pressure. shows 53 lbs at idle. running down the road it never goes below 51 lbs. but on long coasts will go to over 60 lbs, Normal?


cleaned aftermarket cold air intake filter. no change


I have a scan tool and can see map. map increases with engine rpm. seems pretty normal.


I do have a 17 % pulley for many years. cat back, milltek, 8 years or so.
larger injectors installed before tune. Had a RMW tune 4 or 5 years ago.


Water alcohol injection. turning this off makes no difference.


No MIL,s


What else can I check or do?


I have searched forum and tried some of the stuff other people with this problem have done.


Thanks so much for any help. Steve

 

Some of these cars have a "flat spot" in the mid rev range, and it seems as power goes linear until you pass a certain RPM, on average it's right around that 3-3500 RPM range. My car has the same flat spot in that rev range.

What shape is your bypass valve in? Could be time for a replacement.

Compression numbers? Low compression is more noticeable in low RPM.

If there are no CEL lights or codes stored, it is hard to tell you what to look into.

On a side note, what % meth are you running, and is the current tune you are running based on this meth percentile being in place? You can/will run into issues if you are tuned for a meth biased mix and not running it.

 

I know water meth injection was not used when Jan did tune. Near end of tune he turned it back on. It ran fine after tune and ok for a few years after so I'm thinking water meth injection is not an issue. Mostly running it to stop knock.

How can I check bypass valve.

I can check compression, will do that next and post results, she has 92000 miles on her. Low comp is a possibility (hope not).

Like I said, no MIL,s

Thanks, was worried no one would respond. Steve

 

Hows your coilpack look? Lots of corrosion?

 

Corrosion on the post? Some years ago when I put the aftermarket wires on, there was some on one of the posts. Cleaned up with some steel wool. When I put the stock wires back on, didn't see any.

 

If I read your bogging description correctly, I think you're barking up the wrong tree. If you had ignition problems, you would have a pronounced jerky hesitation and would eventually get misfire codes. Start at the simple: how's your belt and specifically do you have good tension on it? Look for at least half a hole in the tensioner bracket.

Typically when the BPV goes, you will be severely down on power across the board. You can check to see if the BPV actuator is at least moving by having somebody rev (IN NEUTRAL) while you shine a flashlight on, and check the BPV actuator arm for movement.

 

Yeah, was doing some searching and I am going to change the belt. It's actually been about 30,000 miles or so since last change. Thanks.

Is NOT down on power above 3500 or so. But will check bpv.

Did not really think I had misfires. Plugs or wires usually show probs under heavy load and no probs up in higher rpm ranges pulling hard. I had these older parts and was easy to change them to see if any difference.

 

Yep, and you would have felt a real jerkiness under load.

 

Ok, belt made no difference. Old 060535 belt had half hole showing. New belt has just slightly more than half hole. It was due for change anyway

Thing runs really good above 3500 rpm. Pulls hard.

Will ck bpv later.

Some other folks had luck cleaning tmap. Will try that also.

Thanks for everybody's feedback. Will keep posting. Steve

 

 

Try turning off your DSC after startup. My MC40 had this same issue and that solved the problem. I have no idea why it works but I was happy it did.