Hi Peeps,






Yes I know this has been discussed many times.
Yes I used the search and all I found was a bunch or solutions that were not the answer.
- check grounds
- add grounds
- clean fuses
- clean injectors
- install a power FC
- change your driving style
- The problem is just the way the ECU does things
bla bla.


Even googling the issue found a bunch of solutions that just didn't make sense for resolving this issue.
I'm also aware this is in the wrong section, and that's because I've just signed up and can only post in this one.
Yes, I literally signed up just to post this so that in the event someone else gets this issue they don't have to waste time doing a bunch of things that will likely not resolve the issue.
So the actual issue.
under light throttle taking off and going through the gears, the car gets somewhere between 2000 and 3000 and has a big flat spot. followed by a kick of power and then its fine through the rest of the revs.
after going reading all the possible solutions everyone mentioned, there was one thing that actually made a bit of sense. and that was someone mentioning that once boost starts to kick in, the ECU switches the fuel pump from low pressure to high pressure, and then kicks in the secondary injectors.
and that it wasn't kicking it in fast enough and caused a lean condition in the changeover.
there was another bunch of things about bypassing stuff to make the fuel pump always be in high mode etc but the info on the low to high pressure led to the problem.


The fuel filter was chock a block full.
with a dirty fuel filter the pressure wouldn't build fast enough when the secondary injectors came online causing the lean condition and the flat spot or hesitation at 2000-3000rpm.
so for $31 problem solved.
car drives smooth as now.
the fuel filter was on my todo list anyway as I only got the car a few months back.
obviously the previous owner neglected this filter because it was in such a bad spot to get to.
also when getting the fuel filter go for a Z520.
Z400 $75
Z401 $196 (and is exactly the same as the Z400)
Z520 $45 or $31 for the Repco equivalent.
Z520 is actually for a Daihatsu charade and the pipe that bends around is angled slightly differently. but still pointing pretty much in the same position as the Z401
car runs beautifully with the Z520.
the Z200 I pulled out of the car, was the most clogged fuel filter I've ever seen in my life. trying to blow air through it either way was like trying to blow air through the eye of a needle.
and apart from the hesitation and not much difference in power between 3000 and 7500, the car ran fine with this dirty filter.
stock computer, catback, JDM so no pre-cat, and 12psi boost. standard turbos running sequential. pod filter and stock IC.
only managed to test power with the new filter in the wet so far and its a big improvement. (only made it to 5000 in third before wheel spin but it was going better)
I only posted the mods so you are aware of the setup incase yours is similar and you have the same problem.
I'm totally aware you shouldn't run more than 10psi and I don't care. it runs better on 12 and A/F were checked on a dyno and were fine with this setup.


Hope this helps someone else with the same issue.


Cheers

 

On my phone and just skimmed thru your post but have you check the actuators?

 

yeah sorry it was a long one.
No I haven't tested them just a visual check.
But there is no problem anymore after replacing the fuel filter

 

I did miss that the issue was solved. Good you caught it and didn't run lean...especially at elevated boost levels. Rotaries DO NOT like lean, you usually don't get a second chance. Not a tuner, but regardless of a/f I'd be careful going any higher on the stock injectors and pump.

 

This is true.
I'm pretty sure I was running lean but knock sensor was doing its job really well because if the fuel filter was anymore clogged, nothing would go through it.
Thanks for the tips though. Hopefully this post will help others

 

I always wonder what that hesitation was around 3000 rpms. Thanks for all the info.

 

good to know. Probably a good idea is to send the injectors for cleaning too. When I bought the car I changed all the fluids/filters (including the fuel filter) just within next couple days. Then a year later decided to have the injectors cleaned. And guess what three of the injectors were out of spec, and the fourth one was dipping instead of spraying.

 

From what I understand, it's a bug in the programming. Seems like it's common with some Mazda cars. I have a Mazdaspeed Miata and a lot of the folks on their boards complain about software glitches and drivability and switch over to a Megasquirt standalone system to fix it.

 

Still fixed? I have the same problem. I replaced the fuel filter and cleaned the mesh filter in the fuel pump. Car only runs well for 2 - 5 mins, then the problem comes back.

 

I know this is a late post but enjoy seeing when other posts have a resolution.
The car continued to run without an issue and the hesitation was completely fixed by the fuel filter change.
I didn't notice any issues with the fuel filter that was used and the car continued to run for a few more years after changing the fuel filter with no hesitation or issues.
Eventually a water seal started leaking a little and the engine got pulled for a total makeover.
Bitman39 it sounds like you have another issue not related to the fuel filter unfortunately. Hopefully you found the issue eventually and it didn't cause you too many dramas

 

this is a classic case for the importance of basic maintenance. troubleshooting should always start there - and that is especially true for a car that's new to you.

 

Long read, interesting thread, interesting insights!