Ok, so after 500 miles on a rebuild, I start getting the 3k hesitation back. I figure it has to be a loose ground, so the first one I check is the one on the UIM. I notice it's copper and it's shaped to maintain pressure on the bolt. I also notice that if you overtighten it, it will lose that pressure. I notice that it has a lot of buildup on it. I clean it, steel wool it, bend the pressure thingy back, clean the bolt, and put it all back together and MY 3k HESITATION IS PRETTY MUCH GONE ! I can still feel the transition to the secondaries, but I haven't cleaned the other side of the connection, or the other grounds. Obviously Mazda wanted this to be a good ground with the copper and the pressure tab, but it's not built to last.

 

Fred,

Our '94 has the same 3K rpm hesitation; I cleaned a few grounds and it went away for about a week. Not the ground you mentioned, though. It's a persistent little devil, isn't it? When the car was new, it wasn't there, and gradually came on around 20 - 30K miles (has 78K miles now). Lots of theories; the one I like best is the "double throttle control" story.

Congrats on getting rid of it (so far)!

---- Bill

 

If you really want to keep that connection solid, try something like this:

http://www.mgchemicals.com/products/846.htm

You can find something similar at a local electronics shop... just make sure it's *electrically* conductive grease (sometimes called switch grease), not thermally conductive heat-sink grease.

It prevents corrosion and keeps a better connection on dissimilar metals.

The kind I have (which I can't find at the moment) is green, and is a molybdenum type grease.

 

Correct URL:
http://www.mgchemicals.com/products/846.html

Thanks, Insane!

---- Bill

 

Where did that damn "l" go?

Hey, didn't realize you're in Fountain Valley!

Try J&K Electronics in Westminster. That's precisely the same place I got the stuff I'm using. I don't think it's same brand as in the link. It's in a white tube.

 

I know J&K. Have been there many times. Thanks!

---- Bill

 

I think everyone I've talked to that's gotten rid of the stock ECU has also rid themselves of the 3k hesitation.

 

I had that problem until I replaced the ECU with PFC.

No more problems.

 

Well, I just added a PMC and it didn't help. Still working on the grounds, and I'm trying the 44k fi cleaner. 3000 - 4500 still have various slight 'pauses' on part throttle.

 

PMC is a piggy back computer, right?

PFC replaces stock ECU entirely.

 

Would someone please spell out "PFC" and "PMC" for me? Thanks!

---- Bill

 

This may be a stupid question but what is

Quote:

UIM

I am still new to RX 7s and terminology. :-) Sorry for the ignorance

 

PMC is Powertrain Management Computer
PFS is Peter Farrel Supercars
PFC is Power Full Computer by Apexi (meaning NOT piggyback)
Also PFS PMC is a repackaged EFI PMS.

Confused yet ?

 

Fred, thanks very much. I'm afraid to ask what "PMS" means!

---- Bill

 

uim= upper intake manifold

 

PMS == Get the hell out of the house!!

 

Update: Disconnected the o2 sensor. Best improvement so far.

 

Sounds like you need a new O2 sensor! Did you have any diagnostic codes, or does your new "PMC not have those outputs?

---- Bill

 

Sounds like you need a new O2 sensor! Did you have any diagnostic codes, or does your new "PMC" not have those outputs?

---- Bill

 

I thought the PFC was a Power Fuel Computer

http://www.apexi-usa.com/electronics_fc.asp

 

New O2 sensor ? I think mine was replaced not long ago. I can feel a couple of very slight flat spots now, 3k is most noticeable. It seems that closed loop mode is creating most of the problem. Not sure why this would happen after 500 miles. Does the ECU adjust over time ?

 

I'm sure you're right but Power Full would have been better ;-)

 

Disconnecting the o2 just makes it run richer which masks the real problem with the stock ECU. I put on a new o2 on my stock ecu and it didn't help the hesitation.

 

I read in a past post that someone fixed his 3k hesitation by grounding the secondary fuel rail. Anyone else try this ?

 

There are a lot of grounds recommended to fix. That is one I've not tried yet and I can see it on the electrical diagram.

I'll tell you what didn't work:

Ground exhaust system
New rear subframe ground
New TSB ground from intake to firewall.
Additional ground from intake to ABS bolt.
Additional ground from battery to shock tower(i.e. Pettit).
Cleaning up factory ground from fuses to shock tower
Additional ground from battery to motor
Cleaning up main ground to trans
Resetting the ECU
New battery
New O2 sensor
Pulling apart as many connectors as I could and cleaning.

All grounds above were sanded off and sprayed with either battery terminal spray or electrolytic grease.