hesitation in MY97 at high revs
 

Hello

can anyone help? my JDM facelift wagon (unmodified) has developed a consistent hesitation/backoff/whatever you want to call it, at engine speeds over 4500-5000rpm. What is irritating is that it has just had a service but I can't be sure if the problem existed prior to then since i'd not really been giving it the slipper so much due to short drives, wife and kids etc. But my feeling is that it's probably begun following the service. It happens every time I exceed that engine speed, and in all gears.

At the service the plugs, fuel and air filters were changed. Nothing else of note.

I've searched the forums but have not found a resolved case which is similar enough to mine, so i have 2 questions:

1/ Any clues?

2/ Is there a cable I can get to check my ECU using ECUexplorer or similar software?


I will check the CEL this evening for fault codes. Cheers for any help you can provide.

dave

Did you have an oil change???

yep, engine oil changed, though I've not had the problem following previous oil changes.

You may want to check the oil level........as if they have over filled, it will get into the vaccum hoses etc?

ah yes, quite right, then possibly foul the MAF sensor? If they've overfilled it, what do I do after I've restored it to the correct level?

It usually fouls up the boost soleniod pipes located on the drivers side by the top strut mount! Give then a good clean out with some brake cleaner etc.

I think you can connect the green plugs together under the dash which will opperate the valve thus help clean it out.......but again not sure about this.

Do you know if they gapped the spark plugs properly?

i doubt they did that. The plugs were NGK PFR6B. As far as I know they don't need gapping for that car.

I had a hesitation problem at high revs/high boost with my sti version 3 for quite some time.
Eventually found out it was the spark plugs that were badly needing changed.

Might have no relation to your problem though as you've said they have been changed.

I'd whip 'em out and make sure they're gapped to 0.65 or 0.7mm... then go from there.

I think the gap is too large, straight from the box. :(

showing fault codes 21 (Engine coolant temperature sensor) and 22 (knock sensor). Going to try resetting ECU. Keen to sort this out before a solo A686 drive. It's surprising that it could be plug gap, difference between 0.8 and 0.7mm. Surely many people have those plugs fitted without gapping them.

If a fault code indicates knock sensor, does this mean it's faulty or it's sensing detonation?


thanks for your help guys
dave

Are they defo at 0.8mm then? If so, then they should be okay (0.8mm is the maximum recommended size for std cars running std boost)

(I didn't know that you knew what the gap was ;))

well, i didn't inspect them, but i checked the box just now and they were PFR6B rather than PFR6B11, which i believe have a 1.1mm gap, so they should be 0.8mm according to manufacturer.

Is the plugs idea that the spark fails at higher revs and detonation occurs, resulting in fuel cut? Any way I can log ECU data (easier/cheaper than removing and replacing plugs)?

If the gap is too wide, then the force of turbocharged air entering the cylinder can literally blow out the spark - which leads to missfires. More prevalent on cars with significantly upped boost levels...

oil overfillling, hesitation, boost control solenoid fouled
 

Chris,you win the lollipop.

Solution: buy brake cleaner, remove pipe to wastegate servo, connect green connectors under dash, turn ignition on so that boost control solenoid clicks and radiator fans come on, spray heaps of brake cleaner into servo hose, several times, reattach hose, reconnect green connectors under dash, start car. Hesitation completely gone.
Prior to this I took it back to garage and asked them to remove 1/2 litre of oil.

Many thanks for the clues Chris, and to all who offered suggestions.


dave

Great! A no-money-spent fix. :)

Really satisfying (you feel smug lol) when that happens, eh? ;)

Well smug, me.

Last car I had was a 1992 lexus LS400 (celsior actually. jap import. pimpin'). They also have a really active online community. When I got it there were several things needing fixed. five seemingly unrelated electrical things were solved with one fuse replacement and a wonky drivers seat backrest was fixed by me with little effort following some online investigation.

I don't think I'll buy a car again that does not have such a community around it. Damn! That means I have to stick to lexus, subaru, mitsubishi, toyota (i.e. chaser) etc etc.

cheers for your help
dave

Hi Dave,

Glad i was able to help......was about 6 years ago when i used to work for Subaru.....so memory not that good. We used to see cars in that has been serviced at local backstreet garages all the time that had been over filled. The maximum we used to put in was 4.2 litres!! It amazing how only half a litre can cause so many problems!!

Chris

Yeah the full oil level/clogged solenoid/w/g is "well-known" issue on the Scoobs...