otter

iTrader: (14)

This one has me stumped, so I figured I'd see if anyone has some ideas. Here's the problem - when I'm cruising, the engine will randomly hesitate, feels almost like I was giving the brakes a quick tap. It's at its worst around 2000-4000rpm (yeah, pretty big range), but I can feel it to some degree across the whole spectrum. Only does it when the engine is warm, and sometimes it'll randomly disappear. I don't feel the hesitation or lack of power when accelerating at WOT, though I do feel it when slowly accelerating.

So far, I plan to test the vacuum and fuel pressure, to see if that leads me to anything. I'll also inspect my injectors to make sure they're clean. Anybody with more experience troubleshooting EFI engines have any other ideas of things I should check? I'll probably check compression, too, though I really doubt that's it, since having a cylinder leak isn't random (I've experienced that before.) My spark plugs are new (first thing I did when this problem came up, thinking maybe a plug was starting to fail) and the PCV valve is clean and working. I'll also pull the fuel pump to make sure the "windsock" filter is free of debris.

What I'd really like to do is throw a wideband on the car and cruise with it, to see if there are any changes when this happens. However, I'm not about to spend $300 just to troubleshoot this.

KreepaEvoX

Thats random misfire, happened to me and I freaked out...just reset the ecu...but let it stand disconnected for like an hour.... to be sure

Just remove some mods and let it run as close as stock as you can for a little while...

morpheus256

O2 sensor. i know when i changed a 20year old one on my mustang with a new one, they sold me a dead one, the car would buck, feel like i was coasting with no power, and do all sorts of weird things with it, at WOT it was fine, unplugged it and ran it back home and it ran fine on the ecu fuel map. and it never threw a cel either

otter

iTrader: (14)

I thought maybe it was a misfire, but no code. Could still be, though. I'll try putting my stock downpipe/cat back in and see what that does. Never did this before I went catless.

I'll also check my O2 sensors. Thanks guys.

MITVRX

Both sound promising. I'd probably get the wideband and that way you can use the wideband for the problem as well as tuning your car for later.

2 for 1!

otter

iTrader: (14)

No tuning in my car's future. I have no plans to dump any more money into this car except for maintenence. There just isn't enough return on investment for this car. I may even de-mod it a bit.

Falcon350z

iTrader: (6)

Definitely check the O2; you can get a direct replacement (no splicing required) for around 90 bucks manufactured by Denso.

I'll tell you though that I just replaced a fouled O2 sensor, and it did none of those things you described -- but mine was fouled out and reading very low voltage causing it to run extremely rich. I have no idea how it would behave if it were entirelly dead.

Definitely check your fuel filters. Apparently there are two on the car, but I have no idea where the second one is... I'm actually searching for it now (which is how I came across this thread). I think you can buy the fuel pump filter/sock seperately in an installation kit for around $30 bucks.

I would also recommend putting some of the fuel system cleaner in your tank. You can pick it up at PepBoys or wherever -- dump it in on an empty tank right before you fill up and see if that helps. It's $5 that may solve your problem.


What happens at WOT at high RPMs, anything?

glgz

Check your MAF sensor to see if it is dirty. I had a similiar sounding issue on my evo. If I was going slow at a low rpm I would get the same feeling. It was more annoying then anything in my case. I used CRC MAF sensor cleaner on mine and the problem was solved. It drove me crazy until I figured it out. I tried fuel system cleaner, spark plugs till I figured it out. Good luck.

otter

iTrader: (14)

No issues at WOT, everything is smooth. I've run a couple cans of Seafoam through the tank and it made no difference, so I'm pretty sure my fuel system is clean. For whatever reason, the Ralliart don't have fuel filters, just a "windsock" looking filter directly attached to the fuel pump. At this point I'm leaning towards the front O2 sensor. I'm going to pull it in the next few days and test its output.

I've cleaned my MAF once already with no difference, but I'm probably going to do it again for good measure. Thanks for the ideas, guys

reTro

iTrader: (9)

It's weird when you ask for suggestions! Hope you figure it out.

stEVOx

some evos i think had a problem like this, it was when the hood is down, the snorkel thing would get stuck/suck on the hood and not let proper air flow in
so maybe check that out

bruce988jl

iTrader: (56)

I don't think he has the stock airbox...
Maybe its the intake filter? Something blocking it?

otter

iTrader: (14)

Nah, intake is fine. Car idles smooth and is fine at WOT, so there's no problem getting air. I haven't had time to poke at this. Should be able to on Friday/Saturday.

DangerousDan

iTrader: (8)

been using the AC? had your timing belt changed?

the AC makes the ECU do extra stuff, might be malfunctioning. this one unlikely.

the timing belt: you have changed it already IIRC. how long ago? the belt could be fatigued, although I think you would notice some power issues under WOT if that were the case. not to metion it's an auto tensioning system, although that could be the cause too. If the tensioner pulley is nearing it's lifes end it could be dragging a little all the time and catching occasionally. grasping at straws in this dept though, as you would see the issue more often than not.

o2 sensor seems unlikely, you would see a cel already if those values were off. does it feel like it's cutting fuel, or just losing power. how you have described it sounds like fuel cut, and if it's fuel cut caused by the o2 sensors you would definitely have a cel.

a wideband would be very useful, but that's limited. do you have the tactrix cable? even with it's limitations on the RA it will give you a decent idea of what the ECU is seeing.

evilralliart

See if this helps, i just changed my spark plugs and i was getting hesitation on the lower RPMs ,car was quitting when the A/C was turn on and this was after installing the new iridium plugs....i cleaned the MAF and the Trottle body and car runs like brand new!(04 sportback ralliart with 88000 miles)