Shifting Tactics

[Flatland2D]

Yeah but as you slow down to a stop from a coast, do you notice anything happenning to the rpm right before the stop?

[Flatland2D]

Forgot to add this in my other post. I've also noticed it's hard to drive at certain speeds like ~35mph because as soon as I step on the gas it accelerates and doesn't just hold the speed. If I let off I'm coasting and slow down. It's a real fine line and can sometimes be really annoying speeding up and slowing down. I originially thought there was some play in the transmission because it's like the power kicks in all of a sudden. Makes the ride kind of jerky.

Now after thinking about the fuel injectors cutting off, I wonder if that's why it's so hard to hold a speed at a low rpm. Instantansous power keeps kicking on and off and makes it real hard to hold a constant speed.

[GasSavers_DaX]

Originally Posted by Flatland2D

Is there any reason why automatics don't do this also? I was thinking they worked the same way. I've noticed in my wife's Civic (automatic) that there's a little blip in the rpm's around 1000 when coasting and coming to a stop.

From what I gather, that blip is the transmission shifting back into first gear from second. I'm sure the automatic hondas do have fuel shutoff on hard decel [it's hard to imagine they would not implement this just because the car is auto], but the auto transmission by nature tries to keep as low an RPM as possible at low to no throttle input, thus defeating [eventually] the fuel shutoff.

I'm looking at my OBD training manals for Hondas, and for MPFI <b>and</b> DPFI systems, it says "if the ECM receives a closed throttle input (under 0.5V), the engine speed is above 1100 RPM, and the engine is warmed, the fuel injectors will be shut off." There is no distinguishing between auto and manual.

[GasSavers_DaX]

Originally Posted by Flatland2D

Forgot to add this in my other post. I've also noticed it's hard to drive at certain speeds like ~35mph because as soon as I step on the gas it accelerates and doesn't just hold the speed. If I let off I'm coasting and slow down. It's a real fine line and can sometimes be really annoying speeding up and slowing down. I originially thought there was some play in the transmission because it's like the power kicks in all of a sudden. Makes the ride kind of jerky.

Now after thinking about the fuel injectors cutting off, I wonder if that's why it's so hard to hold a speed at a low rpm. Instantansous power keeps kicking on and off and makes it real hard to hold a constant speed.

If you're talking about this happening in an automatic, it's probably because you are teetering on the shift speed of one of the clutches inside your transmission. If it's a 5-speed [I had this problem on one of my Civics], I'd look into either a vacuum leak or a dead spot in the TPS as the cause for the bucking.

[Flatland2D]

This is in a manual transmission. I'm guessing it could be a dead spot in the TPS. I do have a small vacuum leak, but I don't think that would cause the problem in the way it is effecting my car. Thanks for the info about that.

[Matt Timion]

Originally Posted by Flatland2D

This is in a manual transmission. I'm guessing it could be a dead spot in the TPS. I do have a small vacuum leak, but I don't think that would cause the problem in the way it is effecting my car. Thanks for the info about that.

If you want I can get a few TPS sensors the next time I'm at the junkyard and send one to you.

[GasSavers_DaX]

Originally Posted by Matt Timion

If you want I can get a few TPS sensors the next time I'm at the junkyard and send one to you.

You should be snatching those up anyhow...pretty hard to come by these days, and dealerships won't sell them by themselves. You know how to get them off the throttle body, right? My brother dropped and broke one of mine and I about cried.

My FITV got messed up and was causing a vacuum leak at one point and my car bucked horribly until I fixed it.


Oh yeah, if any of you honda heads out there want a copy of these OBD training manuals I have, they are VERY informative for the PGMFI and OBD systems on honda cars up to but not including K-series stuff. The zip file is 8MB...I don't have an FTP or anything but I can email it.

[Matt Timion]

I think I'll go get a bunch of TPS sensors at the junkyard. I'll test them with a multimeter and sell them on ebay.

oh yeah...

400th post for me!!

[Compaq888]

Here is how my auto does it. When I'm at speed let's say 30mph. If I want to slow down or just coast I just release the gas and the rpms go to 1000rpm or lower and the car keeps rolling and only loses a little bit of speed.

I usually coast 1-3 blocks If I see a stale green light or yellow or red. If nobody is around I coast as much as 4-5 blocks to the light.

[diamondlarry]

My 1992 Pontiac Gran Prix acts the same way. It seems like it will coast forever by just taking my foot off the pedal.