Misfire or hesitation only when drifting
 

Hi, my rx7 has developed a mysterious misfire. It slightly stutters in a straight line until I hit boost, then it takes off like a rocket ship. But that's not the plroblem. When ever I drift or brake the cars tires loose sideways and go to full throttle the engine misfires very badly and loses all power causing me to straighten up, but if I don't go to full throttle and only go to 70% throttle the car stays sideways and on power. Also the car runs very rich, if I give it the beans the AFR drops to 10.0. It's not the plugs or plug wires. Will test the leading coils soon. The fuel pump sounds weak when I turn it on also. What could it be? Any advice would be much appreciated. Thanks

Upgrades: if they help at all.
13bt rebuilt with 3,500 miles
Bnr stage 3
Stock primaries, 1600 secondaries
Walbro fuel pump
Haltech ecu
V mount

welcome to the board. :)

i'm actually going to go off script here and suggest you look into your electrical system first (grounds, wiring, alternator, etc.).

i won't touch the off-boost stuttering simply because there is a Haltech forum on this board that can probably give you much more meaningful and experience-backed suggestions than i can.

how is your pump wired?

yeah thats the first thing i checked. its a manual switch and goes through two relays for some reason, but it is getting good voltage i think. at idle around 8v when i rev to 3k 12v. seems to slowly get worse. could the fuel pump be slowly dieing? but then again it doesn't misfire in a straight line just when drifting. im going to pull the pump out in a few days for visual inspection. what should i look for?
Really sucks going in to the school year with a broken car and not being able to go to drift events.

thanks for the help!

the pump should always get 12 volts.(when running anyways.)
I would be addressing that.

i won't lie, i'm not a fan of Walbro. however, i know they've been reliable for many people so i'll leave my prejudice right here. that said ... the pump may very well be dying. in my experience with dying fuel pumps, they malfunction randomly, under any circumstance until they finally quit - not just act up in a predictable fashion. so i'm not convinced that it's the pump screwing up, at least, if it is, then it's not acting alone to cause what you describe. at least, that's my thinking.

if you can find a way to monitor fuel pressure and observe what it's doing when the car starts misfiring, then you can know for sure.

check the coils for sure.

also, what plugs are you running?

walbro and a stock reg?? the fuel pressure will be too much at low loads if does not have the 2 speed pump relay still working

if the pump is wired 12v all the time then you need a better ( aftermarket ) fuel reg that is capable of opening further at low engine loads to relieve the excessive pressure

the full throttle missfire may be something else , like the tune being poor there.. overboost cuts ,, or a sad TPS that is seeing a bad part of the sweep and so you get a fuel cut or a throttle pump episode happening

if you have a later haltech unit,, find the TPS deadband settings and widen it,, around 2 % is fine

and should make the ecu ignore EMF noise spikes on the TPS wiring which are maybe making the ecu assume as fast throttle movements that require throttle pump injection timing

A little confused, should my fuel pump be getting 12v all of the time or not? I was told their was a Walbro in it. On the two relays one is 12v/30a and on the other is 12v/40a.
Also if I run the car for a while, then turn it off and quick turn the fuel pump back on it sound louder and stronger than if the car had rested for a week or two. Still not as loud as when I got the car.

If the fuel pump is not pushing enough fuel, weather it be the wiring or the pump it's self, why would it not misfire in a straight line, only when drifting. It makes no sense to me. When the fuel pump was working good I had no misfiring problems , so I don't think it's the tps, and the spark is good and I inspected the ignition coil. It seemed to be good. But as soon as I get the fuel pump working good it's going to the dyno for some tuning.

I'm running NGK plugs.

Also my tps doesn't go through a plug so I can't test the voltage with a multimeter. With the Haltech can I adjust the tps with a computer or not?

Here is the video from the event that the misfiring started at. Wasn't that bad at the even, but now every time I try to drift it happens.


It has music in it, I will try to find the raw film so u can here it misfire

Thanks for the help y'all.

the original fuel pump setup and ECU ran the pump at either of two speeds via speed control relay

at low loads the pump ran at 9 V.. slowing it down


you have now fitted haltech,, and a walbro


the haltech does not do speed control for the pump . and the walbro is a larger pump than the stock one


in this scenario.. at low engine loads.. there is TOO MUCH fuel coming forwards and the stock fuel regulator cannot open wide enough to control fuel pressures

this makes the fuel pressure at times too much down low.. and certainly not regulated about 40 psi above manifold pressures

this makes for a car that at times runs rich down low ,, that comes good when you open up the throttle


as for your WOT issue.. it sounds like something else.. im betting you are seeing noise on the TPS or it has a bad sweep.. and this can enable extra fuel injection ( throttle pump timing ) or cut it ( decel cut )

logging the TPS signal should show that at times it has glitches .. opening the deadband setting will allow it to see up to 2% change before it recognizes this as a real throttle movement