Misfire and fuel psi

D

Darth Vader

Member
I'm experiencing an over 5000 rpm misfire in my car in higher gears. This is definitely noticeable since installing the race pipe.

I thought maybe the plug gaps were too wide but, I noticed on my Dashhawk the fuel pressure is dropping off to between 4-700 psi during those extended times at high rpm. This is definitely not right, correct? As I understand it, if it drops below 1400 anywhere short of redline the pump's giving in, correct?
 
I would say that the fuel pump is probably going bad, or at least can't keep up with what you have done to the car (if anything). I noticed the same thing with my stock fuel pump internals (would dip down to like 700). I replaced them, but now the replacements are bad...I've seen horrendous fuel pressures (dips as low as 400 or worse), and don't dare get into the boost at all anymore until the second replacements come in. Good luck to you!
 
Darth, are you saying that "it just dies over 5000" meaning that the power just dies, but that your fuel pressure is still holding at 1700 at the higher rpm's? But you say fp is dropping to 700 or so during the misfires?

Maybe it is the fuel pump. Are your AFR's still looking good in that rpm range? Low fp pressure at high rpm should be making them look awefully lean, wouldn't it?
 
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The pressure is falling rapidly and, the car is missing and surging over 5K. If it datalogs true, which I will test today, that would explain it all, the dragstrip weirdness, (the nosing over at the top end of the track in high gears), and the misfiring with new flow demands.

I can only watch one thing while I'm trying to watch the roads so, I'm going to datalog AFR, boost PSI and fuel presure after work.

Pressure is ok in the lower gears because the car isn't loaded for too long in the over 5K range. That explains me dropping nearly 8 tenths off my ET but not picking up the expected mph by the stripe.

Eventually, the low fuel pressure would show as lean AFRs but, the sampling rate is still fairly low and it would take some time for the O2 to register that. You'll have long backed out of it because it's making funny noises and running like crap.

I'll take opinions on the best internals here, if anyone wants to share. I'm leaning towards PTP at the moment.
 
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Darth - What year is your car? If 2007 have you checked out the TSB and had it done? What are your mods? Basic mods you should not have FP issues unless your FP is bad.

Edit - Well considering I have went through 4 sets of internals, I would not recommend CDI (which you can't get anyways as they went bankrupt) nor the KMD (Which seized on me almost immediately). The PTP thus far seem good and I will be going that route soon myself. It will be my last attempt on obtaining a good set of internals.
 
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i have the cdi's and they have worked so far (5000-6000 miles) but under heavy load shifting into 4th i lose my pressure....im going to ptp route and getting the whole pump. spend 700 on theirs and send yours in for a core charge and get the whole pump for the price of the internals. easiest and safest way to fix your fuel problems. im getting sick of trying to tune out my fp problems with access tuner. i have 1 more tune to do someone made for themselves and if that doesnt work hello ptp pump.
 
I'm sure hoping the KMD internals aren't crap...I just spent a lot of money on them :( Where did you get the PTP internals? I can't seem to find their website or find a vendor who sells them.
 
http://www.pt-performance.com/

with this shown....shop protege garage for all your mazda parts! KMD's should be fine. ptp sells the cheapest pump i could find so im going for them. so far no bad news from ptp fp upgrades. kmd's work great. i just want the whole pump and cp-e's pump is to much for me.
 
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I sure hope so. I have bought most of my stuff from PG, but I got worried when I saw they seized for Bravnik. I hope they work...I am starting to really dislike driving around like this.
 
Bravnik said:
Darth - What year is your car? If 2007 have you checked out the TSB and had it done? What are your mods? Basic mods you should not have FP issues unless your FP is bad.

Edit - Well considering I have went through 4 sets of internals, I would not recommend CDI (which you can't get anyways as they went bankrupt) nor the KMD (Which seized on me almost immediately). The PTP thus far seem good and I will be going that route soon myself. It will be my last attempt on obtaining a good set of internals.
Click to expand...

It's an 08 with a full set of breathing mods, in and out, barring a front mount.
 
TSB? I have a 2007 and haven't heard anything about this. What is TSB? Is it something I need to take my car to the dealership for?
 
The Dashhawk tells the tale. The FP is sort of randomly shitting the bed. I did 5 logs, 4 in 4th gear WOT from around 4000 rpm, til a max of 6000, one in 5th, ~3-6000.

On the first DL I hit it twice. On the first hit, pressure died to under 800 and on the second, it held up to about 1700.

On DL 2, it straight crapped out and dropped off to about 700 psi during the runup.

On DL3, It did it again, crapping out to around 700.

On DL4, it held up ok for most of it, dipping only once to 1000 for a brief time.

DL 5 was ok all the way up, staying at around 1500 to 1700 psi all the way.

So, WTF? The pump works sometimes and not others? This car is possessed? Usually parts don't come and go like this; either they are fragged or they aren't.
 
Here's another weird detail: In my obsession with pressure, I didn't look at the AFR.

ON all 5 datalogs the AFR never rises above about 10:1, no matter what was happening with the pressure or boost levels.

Is the sensor resolution too low or too slow to note the change from dropped pressure or is that a real measure?
 
Well, here's what I found when I was doing my log.

First off, some background...I was noticing a huge drop in boost pressure through the revs (like down to nothing) and figured I had a messed up BCS and/or a boost leak. So I logged fuel pressure, AFR, boost, and WG%. I noticed that the WG was open 100%, boost dropped off to 0-1psi, and fuel pressure droppped down to like 400psi or less...but AFRs were still OK. I think it does everything it can to save the motor...in my case it was dumping all of the boost. At lease that's what I HOPE is going on, because that is the path I am going down to fix it. If I fix the FP and the boost is still going away I'm not sure what I am going to do.

Log:

3rdGear9-27-09.jpg


@ 4918 rpm:
Fuel Pressure = 278 psi
Boost = 0.73 psi
Wastegate Solenoid Duty Cycle = 0.0%
Air/Fuel Ratio = 10.10

Note: since that one run I have been driving more carefully than I did for my driver's test. I haven't been in the boost once since. I've been able to keep fuel pressure up in the 1500 psi range, which still isn't good...but it's not <300psi :o
 
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The dealio is, according to Mazda, anything under 1669 psi at >60% load PID and up, is junk. Mine's at 700 under WOT so, there you are.
 
bykeryder4life said:
dude **** these damn cdfp's. they totally suck and are full of fail. sorry to hear darth, good luck fixing them...
Click to expand...

Not to discourage anyone but I haven't heard too many ppl having great success with any aftermarket fuel pumps for this car. Seems like every vendor/manufacturer have had either QC issues or the upgraded pump doesn't work as advertised.
 
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