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Thread: Part-throttle hesitation

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Posts: 1-10 of 27
2009-10-06 16:36:42
#1
Part-throttle hesitation
Since swapping trannies in my car (to a B15), I've been experiencing increased hesitation under part throttle. I have a '91 SE-R with bolt-ons. I used to get "bucking" occasionally in crawling bumper-to-bumper traffic when I was in first just above idle rpm and light to no throttle. Now I am getting pretty significant hesitation under part-throttle, especially when the car is cold. When I swapped trannies, I went to a lighter flywheel and I don't know if the loss of momentum is making the original problem more pronounced?
I have looked at a lot of hesitation threads and found it can be just about anything. Idle is good, although after going a short bit at part throttle and then pushing in the clutch, the rpms can drop really low (even stalling) before stabilizing at 800rpms. Full throttle is good too.
I recently did a tune-up. Yesterday I pulled the plugs and they looked fine, just a bit used. I used DCScotty's method for testing the MAF, and I think it looks fine. Here's the pic of it:


I am very much a novice when it comes to these things, so please bare with me as I try to implement your suggestions. Thanks in advance!





Edit: The problem is now fixed! I changed a couple of things at once, so I'm not sure which was the culprit. I will outline what I did.

If I had to guess, I'd say that this was the root of my problem:



It had a crack in it and was leaking oil and probably screwing up the air readings. It was located to the right of the headers and went up to the emissions stuff on the front of the engine. Here is the replacement hose:



Other things I did:

I cleaned out the EGR, BPT, and the accompaning metal tubes. Here's a link to a thread with some resources on how to do that:

http://www.sr20-forum.com/general-sr20/23980-can-someone-make-detailed-how-clean-egr-thread.html

Then I replaced all the vacuum hoses I could get my paws on, a few of them looked kind of shady. The last thing I did I don't believe had anything to do it, but just in case, I took off one of the "boxes" that's attached to the intake and plugged it with a 1" PVC end cap:



Now my car is purring. If you have a similar problem, I hope this helps.
2009-10-06 16:47:02
#2
i have seen a waterpump cause this problem, it would hesistate and also have a certain spot where you would hold the throttle it wouldnt accelerate at all.
2009-10-06 16:47:24
#3
I thought this was just normal function of the newer SR trannies? I know my 99 G does it and people I have asked with the 00+ G's also buck. It's happens much more then in any other car I have ever driven in. I hope there is an actual fix so keep working on it .
2009-10-06 17:18:31
#4
my 99 g20 likes to buck sometimes if I let off the throttle and decel in first but never if im accelerating slowly from a low rpm. Check for vacuum leaks that could be whats causing the idle to drop down when you let off the throttle.
2009-10-06 17:21:33
#5
Sneaky mine does the same, never figured out why. If i stay in gear and let it decel in 1st it will jerk like crazy. Sometimes when i touch back on the gas if i dont pull it out of gear, the initial touch of throttle makes it jerk as well.

Never could figure out why.
2009-10-06 21:03:04
#6
Got the same problem. Bucks at part throttle in 1-3 gears. Kinda annoying. somebody figure it out
2009-10-06 21:10:38
#7
Originally Posted by sr20monkey
Got the same problem. Bucks at part throttle in 1-3 gears. Kinda annoying. somebody figure it out


Which engine and tranny you got?
2009-10-07 03:24:24
#8
mine doesn't do it in 2 or 3 maybe just a tiny little studder at but not jerk. It just does it in decel in first sometimes and that's about it.
2009-10-11 02:29:42
#9
u13 det stock tranny. i upped the fuel pressure by about 2-3 psi and its good not. only happens when it cold. works great if you punch it.
2009-10-11 02:51:21
#10
same thing happened with me.took my motor out, changed the clutch/flywheel, put a bigger turbo on it(went from t28 to gt2871r) and now i have this wierd ass hesitation/bucking at part throttle but WOT it runs awesome
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