I have heard that the 3k RPM stutter is a normal thing and was wondering if it is a bad thing. ie, if I set the cruse control at 80 in fifth which puts the RPMs at 3k, they every now and then it feels sorta like an ignition stutter or something, the boost goes up on the gadge, it feels like the car takes off for a split second with the gas pedal motionless. I don't know if all of this is just the 3k RPM thing, but any input would be great.

Thanks
-Streetdreams-

 

My A/F gauge completly goes lean (like all lights off) when it goes around the 3k area. I have no idea what it has to do with it. Maybe the motor doesnt get fuel for that second or God knows. Hell I know Mazda doesnt even know.

 

I heard that disconnecting the O2 sensor will fix it. Not sure about that, as I've never tried it. I DO know that a PowerFC fixes it...

 

According to Doug at EFI, the problem is very clearly a logic fault in the stock ECU where it is momentarily firing both injectors at about 3k rpm when the secondary injectors come on line. I may have the details confused but I believe that was the gist of it. Not clear to me how that would make you go lean - just passing on the explanation as I understand it.

 

If you do a search you can find a lot of info.

It has to do with the injectors switching from the primaries to the secondaries and not overlapping exactly. So for a second you lose power since it doesn't have any full. Not anything bad, just really annoying. I wouldn't disconnect the O2 sensor though...

Blake

 

If that's the case, then explain why not all FD's have the hesitation and also why they didn't roll off the showroom floor with the problem?

There is more to the 3k hesitation which is why no one knows exactly why some fixes work for some people and not for others.

 

Well, thats the best explanation so far. Its possible it was an ECU problem, and some of the posts say grounding kits fix it (doesn't make much sense to me, but I haven't tried it).

As stated by Fatman, his A/F gauge goes lean ( hrm...loss of fuel ), and the injectors DO switch over at 3k RPM, or right around there, based on load, correct? Oddly enough, I've never heard of a situation in which it hasn't been fixed by changing the ECU. My research hasn't been extensive, but I have been told changing to the PFC, etc, fixes the problem. I currently have an XS reflashed ROM, and I still have the same problem. All that points to the ECU, and some form of fuel cut to the injectors. That coupled with the ECU programmed to switch injectors at that time, the explanation I have heard, and I go by, makes more sense than anything else. If you have another explanation that fits the evidence better, I'm all ears.

I'm not an expert, and in fact would barely call myself a novice, but if you can't provide a better explanation, don't come trying to rip into mine.

Blake

 

My stock ECU didnt have this 3k RPM hesitation.
When I installed another M2 tuned ECU (from jpandes forum member) I got this 3k RPM hesitation.

You think this clears the mistery ? Jpandes didnt have this hesitation on his car.

No go figure...

 

Has anyone tried using a brand new stock ECU? Just wondering if there is an internal grounding or connection problem.

 

The 3000 RPM hesitation has to be the number one n00b question that is asked weekly on this forum.

Right up there with "what is a AST" and "which type of oil should I use".

 

Also along with the going lean thing, I think it also may have to do from running loop (like getting info from the o2 sensor) to running off the map. Thats just another understanding I have. Then finally the lean may be understood from what Ive heard that the fuel pump switches from low to high setting and that split second or w/e gives you the hesitation.

 

story goes the maps changed after a 20k mile 'break in' period, then the hesitation started for most of the cars. none had it out of the show room.

with fast response narrow band gauge, no problem with almost cold engine, when o2 loop is first active. max problem with 1/2 warm engine, slight vac to 4-5 psi load .... all lights out ie zero volts at O2 sensor for 1/2 sec. modest problem engine warmed, same load.

transition from pri inj to pri + sec drops the fueling ball. would be nice to see datalog of analog inj volts at pri and sec across hesitation.

100% cure is pfc, or any ecu but stock.

 

Well, that story doesn't work for me as I didn't switch out my stock ECU until the car was around 60k or so miles. I didn't own the car for the entire 60k miles, but the part I did own it, it never had the 3k hesitation. Using the Pettit ECU now doesn't show it either.

There are more people who never ran into it either. I would wager more on injectors not flowing as well as they should along with the way the stock ECU handles the fuel around that area. Switching to a different mapping may hide the problem which is why the PFC "seems" to fix it.

 

It be nice to see this also with a fuel pressure gauge and see if it drops. (Not through a PFC cause that seems to fix it )

 

you are completely consistent with story .... one of the lucky 49 max percent FDs with no problem ever.

 

I believe Mazda itself adressed this issue. There are a few types of stock ECU's and a few have this issue and some dont. I have seen posts on the forum which will tell you exactly which of the stock ECU's have this problem but I am too lazy right now to search for it. I had the N3A1 Cali ECU which had the problem and when I got my PFC it went away. But like formerporscheguy said, this question is asked every week so do a search.

 

I don't know, Ive got a PFC and get some lurching at 3k. It's minimal but it is there.

 

Then the ECU isn't the problem.

The whole thing about the ECU changing it's programming after 20k miles is ridiculous. That would mean an FD at 20,001 miles would have a different dyno and/or power rating than one at 19.999 miles on the odometer. That's just crazy. And the multiple programmings of the ECU doesn't rate much better IMO. There would have been a TSR released about it which definitely would have surfaced somehow after all these years if that were the case.

Simple fact is that there is no one cure as the hesitation, while occuring in the same area for a lot of people is probably all caused by different symtoms for different people (hence why some fixes work for some and not for everyone). Simply saying it's the ECU is not correct.

While some people believe in blind faith that the PFC solves the problem, IMO, that's not the case. IMO, the PFC may "hide" the problem (or make it un-noticeable), but as some people have mentioned that they still have hesitation even with the PFC and I've also heard the same thing with the PFS PMS.

 

Not to mention that the ECU doesn't keep track of mileage, the speedo does

 

Oh yea. I forgot the speedo has that quick-rom-flash thingie that goes off at a certain mileage.

 

So wait, those of us with the 3k rpm hesitation can buy a new gauge cluster from Mazda, which will read 0 miles, and be done with the hesitation right?

 

I too have this hesitation and agree with Mahjik because by now, these cars are 8-10 years old and many different configurations (mods). This like contact corrosion, clogging injectors, and different maps, etc. I'm still working on mine, I have new ground wires waiting to go in and a PFC but I'll wait and see.

 

Ok, so Mahjik, I've gotten a bunch of bits and pieces, but not yet heard your exact theory. I fail to see how the injectors not flowing the correct amount would be the problem. That either means they don't flow properly most of the time, or the signal they are receiving is incorrect.

I was paying attention to it on the way to work, and noticed that when I drive normally off the line, if I rev it up to 2-2500 RPMs and let the clutch slip its much more likely to hesitate, if I let off at a lower RPM, it doesn't happen much at all. Also, of course, full throttle it doesn't happen, I assume that would be because the injectors are already switched or both on, or it changes the map. Lower gears makes it worse, generally.

Blake

 

Not to beat a dead horse, but...

I agree that it is not the ECU because I have the hesitation with an aftermarket ECU. However, I'm not sure about the hide/fix distinction. I don't really see a difference, if the 3k hesitation is gone, then it is fixed. Correct me if I am wrong.

 

Not true. If the ECU isn't the cause of the hesitation, but lets just say a contributing factor, and switching it out makes the hesitation go away, you've basically just put a band-aid on the problem.

It's analagous to many people's view on the engine torque brace (Mahjik included if I remember?) Many people say that if the stock engine mounts were in good shape, then the engine would need an additional support. Adding the ETB cures the symptoms of the problem, i.e. the powertrain moving, but it does not solve the problem.