when I go 1/2 throttle under boost, between 2k and 3k the car will hesitate. It's not jerky or anything bad. It's just barely noticeable. I've been trying to trouble shoot it for a long time. It seems to go away as the car warms up, but even at operating temperature I can still feel it slightly. The engine has less than 1000 miles on the rebuild, no cracks or intake leaks anywhere, Did an extensive grounding mod, replaced the ECU, installed different sized restrictive pills, and even tried to tune it out with my Apexi AFC. That mini hesitation at half throttle is bugging the crap out of me man.

I don't have many engine mods except for an S5 turbo on an S4 engine. If anyone can throw some ideas at me, I'd appreciate it.

 

tps?

 

vacuum?

 

TPS checks out, I guess I could have missed a small hole somewhere with the vacuum tubes. But I checked them out for the most part and it looks okay. I'll try replacing them all and see what happens.

 

I think my issues are due to my fuel pump. The last owner said he installed a Walbro, but I never checked it out. I pulled back some of the covers during lunch break today and It doesn't look like any custom wiring was done at all. He might have installed it on the stock power and grounds. I don't think its giving enough fuel in the low RPM range while under boost. Is there a quick easy way to test my fuel pump low rpm voltage? Or do you guys think I should go ahead and do a rewire?

 

I also installed a warblo for a little while and the wirng was all the exact same after i was done so don't make any assumtions.

The only way to know is to pull the pump and see what it looks like. Also, the fuel filter could be cloged.

If you see rust on the pump sock then i am betting that is your problem.

BUT it should have problems allt he time if it was the fuel pump, not just at 1/2 gas.

Only way to know for sure is to get a fuel pressure gauge.

 

One of the reasons I think it may be the fuel pump getting low voltage is because when I have my radio completely unplugged, it seems like the car runs a little bit better. I know there isn't anything wrong with the engine wiring harness because I replaced it with a refurbished one. But I think I have a bunch of problems with the cabin side. Stuff like, the windows working very slowly, and the beep the car makes with the key is still in the ignition sounds very poor.

Also, the hesitations are very minimal when the engine is at operating temperature. but when cold at WOT on boost under 3k the car will buck violently. I also have never been able to coast in gear at low RPM. I originally thought it was a TPS problem long ago, but I readjusted my TPS like 2 years ago, and I still had this problem back then. I remember it being within range too. Maybe I'll just fork out the money for a brand new one from Mazdatrix.

 

Bump.

Another thing that might help put a finger on it: ~ If I drive a little hard the car will actually idle higher at a stop. If I were to floor it in 2nd or 3rd and then come to a stop light the idle would be 1.5k or more. Then I would drive it and not boost at all and at the next stop light it would idle absolutely perfectly at 700.

 

It could very well be a fuel problem.

As i said above the only way to find out to to pull the pump. take a look and see what it is like. Only takes 5 mins. Then test the voltage to the pump as well (with the pump still connected of course)

 

That did it! The fuel pump wasn't reading at 12v. So I did a rewire, the car idles better and all the hesitation is completely gone. If anyone else has this problem at low rpm boost, its probably going to be your fuel pump not getting enough power.

 

Good to hear you got it working, i might need to try this.