Initial hesitation and faint pulsing !

[youngsyp]

Chaps,

I thought I'd start a new thread as, I can better describe the symptoms and, I've changed all the consumable ignition parts (leads, plugs, dizzy cap and rotor arm), with little effect.

Basically, the car idles and starts perfectly. On light to medium throttle inputs, it also behaves impeccably. It's when you go from medium to high throttle inputs that it misbehaves. Basically, on initial medium to heavy press of the throttle, there's a momentary hesitation, then the car picks up and it's off. When you have your foot flat to the floor, as the revs build from 4.5k ish upward, there's a very faint, what I can only describe as, pulsing. Like a slight dip, then power, slight dip then power, all the way to the red line. The car still feels very quick though. I've also noticed, if you hold the throttle in certain places, with little load on the engine, the car will 'hunt' and hesitate.

As above, I've changed all the consumable ignition parts, although, I had to reinstall the OE coli lead as, the new coil lead have a hole in one of it's insulation boots.
The plug gap is factory preset although, I checked it and it seems more like 0.7mm than 0.8mm ! The plugs are NGK IX 8's. I've reinforced the earth to the TPS, cleaned the TPS with WD40, reinforced the earth on the MAF, reinforced the earth on the fuel pump that sees 12.27 volts and the car has a earth bonding kit fitted. Timing is set at factory 20 degrees BTDC. And it's fault code free.
It has a Blitz filter and Hayward & Scott 3" elbow and downpipe to 2.5" decat exhaust system. A Cusco oil separator that vents to atmosphere. Original breather system removed, including rocker cover to inlet piping. TMIC with partial heat shielding. My AVC-R is set to 1.00 kg/mm (the car behaves the same with the AVC-R set to 'off' although, I don't recall it 'pulsing' ?!). It holds boost without the AVC-R turned 'on' but, you can see it fluctuate by 0.01-0.02 when the 'pulsing' is felt, when the AVC-R is set to 'on'. It's only ever run on Optimax/V-Power. And I've recently seen 300 miles a tank, when using A roads with mixed driving and frequent over taking.

It started misbehaving after a week of 150 mile a day journeys !

I think that's it, please help !

Cheers

Paul

 

[AJ4]

fuel filter been manked up by the long journeys ?

 

[Odin]

Or maybe its that little box before the dizzy thats playing up, I've no idea really, But you didn't say if you had checked that....

But it could be as ross said or maybe even the pump isn't working properly. Who know's lollollol


Rob

 

[youngsyp]

fuel filter been manked up by the long journeys ?

Well, it's not that old and the last time it was off (to change fuel lines) fuel came out clear at both ends. That was a couple of months ago but, I will check it this weekend as, I do have a tendancy to run it low on fuel !

This does seem to be pointing at the fuel side of things though, doesn't it ?!

As it seems to happen under load, and I have the original fuel pump, I was wondering if the fuel pump ups flow according to load or, does it always run at the same rate and the FPR regulates flow and pressure ?!

 

[youngsyp]

Or maybe its that little box before the dizzy thats playing up, I've no idea really, But you didn't say if you had checked that....

What little box would that be ?

I've checked the coil and amplifier (I think that's what it is) and the appear in good condition, the plugs to them are in good nick too !

I have to agree though, it could be anything :lol:

I'm tempted to get it on some rollers and get them to do a diagnostic on it, instead of throwing money, blindly at it !

 

[youngsyp]

Does anyone have the resistance specs for the coil, ingnition amp and injector resistor thingy's ?

 

[pulsarboby]

have you done a kv check on the leads (with a meter) at different rpm? this will tell you quite a lot, ie what lead or cylinder, injector is playing up! may also be worth carrying out a cylinder balance test.

as for the amplifier (ignition module) which rob is talking about, this will 99% only play up when engine is hot and module will over heat causing difficult starting untill module has cooled down again (generally its the heat seek on back of module that erodes), so i doubt very much that its that!

assuming you have done a fault code check and its coming up clear, and all leads and ignition system are ok. then i would have to plump for an injector which could be malfunctioning at higher rpm (may have a bit of crap in one of them) this would cause a slight misfire as fuel on that particular cylinder will not be atomising correctly.
hope that helps mate!

 

[youngsyp]

The thing that's annoying is that it's only under specific circumstances that it misbehaves which, I think would have highlighted the cause. However, due to it only happening with load, and not starting and normal driving conditions etc... I think a duff coil or ignition amp can be ruled out.

I wouldn't have thought it would be a dirty injector;
1. due to the fuel filter being in place and
2. due my constant usage of Optimax/V-Power and it's associated detergents.
The suggestion of the filter being dirty is feasable though, due to the way I run the tank down !

Has anyone had similar circumstances to me ?

 

[AJ4]

I had a similar problem once and it turned out to be spark plugs. Can't remember the exact brand ( I think they were HKS ones ? ), but my engine just didn't like them, no matter what gap I ran at. Probably not your problem though, unless you've changed your plugs recently....

Possibly its something to do with wastegate / dump valve. Under certain vacuum conditions somethings opening or closing when it shouldn't ?

 

[pulsarboby]

yeah granted, but ive known many an injector to suffer from either a small particle of dirt effecting spray pattern or a sticky injector will also give a similar symptom.
as aj said change the filter, although i do not think this is the problem (sorry aj) as a gummed up filter will cause big problems at the top end of the rev range where you require more fuel.
but however if tank has run very low it is possible that you have picked up some crap which has bypassed the filter (either due to it being blocked) or just a small particle thats all it takes! so if you change filter get some injector cleaner and fill filter up with it then fit, and put the rest of injector cleaner in tank.
if there is a blockage in injector this may well clear it!
at the end of the day your problem is a misfire caused by something!
you have basically eliminated ignition curcuit by changing parts.
so this leaves the fuel circuit.
process of elimination!

 

[BLONDIE]

Mine is doing the same thing, cant work it out, let me know if you find the problem mate

 

[youngsyp]

I can see where you're coming from but, I'm still not convinced...sorry !

Anyway, I went over to a rolling road place to see about a possible diagnostic run at lunch time. On the way over there and back, I played with the car a bit and the misfire/hesitation seems very sporadic. Sometimes the car is accelerates very strongly, others it'll hesitate momentarily and then take off. Other times there will be a strong hesitation when I back off the gas/trail the throttle. All in all though, the car behaves inpeccably and smoother than before I changed the ignition parts. Acceleration also feels stronger than before too !

To me, what it feels like is water on a plug or cross arcing of a lead ?! Basically, from how well it's running, ignoring the hesitation and misfire, I think it's some as simple as this...or maybe the plug gap is too large ?! I'm getting more and more convinced that it's ignition related !

One thing I did omit is that I emptied my catch tank whilst brain storming and it was half full of water ?! Also, after changing my plugs a revisiting them, plug hole 2 had water in it. Since then, the plug hole appears to be staying dry and the catch tank remains empty !
And, there's no 'mayonnaise' around the oil filler cap or rad cap. Coolant remains as new and inside the rocker cover looks very clean as usual !

As for the wastegate, it's holding boost solidly when the AVC-R isn't on so, I've rulled that out. The SSQV shouldn't open when under load due to being a pull type BOV so, that made me think that wasn't the issue ?!

To say this is bothering me is an understatement as, it's never misbehaved once in the 4 years I've had it up until now !

Thanks for all your ideas so far though, they're much appreciated !

 

[BLONDIE]

also my catch tank was full of water when i got it serviced, i had a leaking cam cover gasket which was filling up my spark plugs, they fixed the problem and after a week i started having the same problems as your self, the spark plugs were renewed but not the leads and im just about to replace the dizzy cap and rota arm to solve the problem but i see you have already done this and it hasnt fixed the problem? a friend advised i had a compression test done?

 

[youngsyp]

also my catch tank was full of water when i got it serviced, i had a leaking cam cover gasket which was filling up my spark plugs, they fixed the problem and after a week i started having the same problems as your self, the spark plugs were renewed but not the leads and im just about to replace the dizzy cap and rota arm to solve the problem but i see you have already done this and it hasnt fixed the problem? a friend advised i had a compression test done?

Hhhhm, interesting. My rocker cover gasket has needed replacing for some time and I could have sworn that's where the moisture came from to fill the plug hole. It would also explain the catch tank being full. That's a lot of condensation though, I wonder if it sucked some back through some how ?!

I'm not worried about compression (famous last words) as, it pulls very strongly when not misbehaving and if it was a ringland gone or valve sticking, I'm assuming it would be down on power across the board ?!
If you can do a compression test easily, do one for peace of mind !

I'd continue the course your taking and do the leads aswell. Try here: www.performanceleads.co.uk These are what I bought. Essentially the same construction as the Magnecor KV85's but, for 1/2 the price of OE leads. The service is excellent to, they came the next day ! I did have an issue with the coil lead (whole in one of the boots) but, they've just sent me a replacement out no questions asked !
I measured the resistance on the new coil lead and the old Nissan lead had 2.5 times more resistance ! Wether this was down to age or just how good the new leads are, I don't know but, the new lead measured 1k ohm of resistance and it's about 6" long which, seems quite low to me ?!
My leads were over 4 years old so, needed doing !

Good luck and if I sort it, I'll let you know !

 

[BLONDIE]

CHEERS MATE
iv just been on another gtir forum and a bloke on there was having the same problem, he replaced the actuator and it solved the problem, just an idea!

 

[youngsyp]

Yeah, I did think about that but, mine holds boost perfectly !

It's a thought though, I might check for play in the rod !

 

[gtirx2]

Mine done the same sort or thing the other day if i was in the low rev and put foot flat to floor it would pulsate up untill the turbo kicked in and then go away but still not pull as strong as it should.
I regaped the plugs to 0.7 and reset and advanced the timeing a little and it seems to have gone?
Proberbly just luck but i would check your timeing all the same.

 

[youngsyp]

*UPDATE*
I found the problem over the weekend !
Going on AJ4's advice, I took off the fuel filter. Initially, all clear fuel came out , then it came out black ! As I didn't have a new filter to put on, I attempted to clean this one out with fresh fuel. Whilst blowing through it, there was a sensation of it becoming un-blocked, like a small thud. After that, it was very easy to blow through ! So, a new fuel filter will be on order today !
I also went round the engine and undid all the plugs I could find and sprayed the contacts with contact cleaner. Same thing with the MAF sensor wire. Checked the plug gap and it was still 0.7 mm so, I left that.

I laid the cable for the fuel pump re-wire so, that's the next job !

Anyway, thanks to everyone for you comments, especially AJ4 !

 

[azboy]

mine seems to have the same proc look forward to seeing what it is, drives fine 1 day then messes around.

 

[adamsgtir]

hi did this solve your problem ????? mine is doing this and it is very imbarassing at the lights.