Clutch or Boost issue [advise pls]

[rooks]

Hello everyone,

The VR4 in question is a 1996 manual which is completely stock, in terms of airbox, exhaust, boost, fmic etc.

A bit puzzled with the current hesitation with the normally good acceleration of the car. Perhaps to my peril I had experimented with three full tanks of 95 RON instead of the usual 98 RON. After the third fill using Caltex 95 the car hesitates on acceleration, where the RPM would race up to 4000-5000 on 2nd gear and the boost sitting on 0 psi or below. The normally responsive boost was missing! The car felt sluggish.

After searching the forum the problem sounded much like a clutch issue, i must admit this morning there was clutch shudder on one first gear take off which went away after the engine warmed up.

What happened 800km ago:

oil and oil filter change
throttle body clean using throttle body spray (i immediately drove the car after the clean)

What did i do today:

Checked all hoses and cables around the throttle body area are connected correctly. including MAF sensor cable.
Filled with 98RON
Reset ECU

The car is still capable of boosting to 5psi if i give it around 80-85% gas ...100% being flooring the gas.

Finally today to test the clutch, on idle i put the car on fifth gear, handbrake on, rpm up to 3-4k then slowly released the clutch and the engine stalled immediately, I'm hoping this would rule out the clutch issue.

The car has not had a change of timing belt, fuel filter and spark plugs...perhaps these could be the next troubleshooting steps? I would hate to think the poor accerlation had some to do with the timing belt, scary stuff.

Bit puzzled here....hoping for advise from the ozvr4 experts.

 

[Hotwire]

Hello everyone,

The VR4 in question is a 1996 manual which is completely stock, in terms of airbox, exhaust, boost, fmic etc.

A bit puzzled with the current hesitation with the normally good acceleration of the car. Perhaps to my peril I had experimented with three full tanks of 95 RON instead of the usual 98 RON. After the third fill using Caltex 95 the car hesitates on acceleration, where the RPM would race up to 4000-5000 on 2nd gear and the boost sitting on 0 psi or below. The normally responsive boost was missing! The car felt sluggish.

.....

This will definitely have an effect here. The high octane fuel & ignition maps are designed for 100RON jap Fuel. The Low octane map is exactly that, after experiencing enough knock events from the knock sensor the car will reduce timing and increase fuel in the highest load areas - right where you are indicating you are feeling the "dip". The ECU will maintain the 100RON map with a few minor knock events on 98RON fuel, however should not trend/interpolate to the low octane map.

The fact you mention 0psi is very odd however - how is this being measured? and how does the boost build/drop throughout the entire rev range?

You have put 98RON and reset the ECU. Run it through a full tank of 98 to ensure you are operating on the high octane map and let us know if the hesitation persists..

 

[Buckas]

firstly, you run 95 in your car while still accelerating hard??

i dont think it'd be clutch, you'd notice if it was. if it was wearing it'd slip under full load and the revs would increase faster than the speed. you can test this by putting it in a higher gear and driving up a hill

maybe boost leak? check all intercooler hoses and other associated boost lines. but i don't quite understand what you've said about the symptoms ("the RPM would race up to 4000-5000 on 2nd gear and the boost sitting on 0 psi or below. "). is your gauge reading zero under acceleration?

 

[unclepaulie]

if its not boosting its a turbo problem, either turbos them selves or pressure issues. check all your vaccum lines and report back. maybe wastegastes are stuck open, could be a lot of things, start with the easiest fixes first

 

[rooks]

Thanks for the quick responses guys..

This will definitely
The fact you mention 0psi is very odd however - how is this being measured? and how does the boost build/drop throughout the entire rev range?
You have put 98RON and reset the ECU. Run it through a full tank of 98 to ensure you are operating on the high octane map and let us know if the hesitation persists..

Lee,
I hope its as simple as bad fuel, will run through the full tank of 98 RON and report back.
The boost/vacuum gauge which measures on PSI stays below 0 PSI which I would assume to be vacuum while accelerating on 2nd to 3rd gear at around 4k - 5k RPM, normally I would reach positive readings (slightly above 0PSI) when i exceed 3k RPM on 2nd gear....hence the sluggish feeling of the car.

Dan, Yes a boost leak sounds possible too, will check around the engine bay and under neath the car after work today and report back.

On the way work I tried boosting on different gears, found that 2nd and 3rd was still non responsive in building up boost while 5th gear registers 4-5psi of boost on 3.5k-4k RPM. I suppose this is better tested on a quiet FWY later tonight!

Paul,
at this stage the turbo is still capable of boosting to 5psi but only on the higher gear ranges...4th and 5th. Seems hard to accumulate boost pressure on the lower 2nd and third gear. mind you have not floored the car on 2nd or 3rd.....not much of a floor-er, tend to baby the car .
will check vacuum lines too and is this what im looking for in terms of wastegate? image stolen from a turbo repair site.

 

[Hotwire]

Thanks for the quick responses guys..
Lee,
I hope its as simple as bad fuel, will run through the full tank of 98 RON and report back.
....

Andrew, its not BAD fuel, its the WRONG fuel. 95 is to low octane for consistent performance in a VR4. 98 RON is the minimum you should run.

As for the boost figures - you really need to run through 2nd & 3rd at Wide Open Throttle (WOT) or floor it to determine what boost you are making. At different percentage of throttle you will get different boost at the same revs. i.e. 1/4 throttle at 3krpm may give you 0psi manifold pressure, while 100% throttle at 3krpm will give you around 8psi (give or take a few). So please "floor" it before reporting what your boost levels are again.

 

[rooks]

Update:

Jacked up the car, opened bonnett and started the engine, listened for hissing around the engine bay and fmic.

1) took off positive and negative cable for the battery then pumped the brakes. (reset ECU)
2) took off snorkle and air filter box. replaced dirty hks filter with repco paper filter.
3) tightened jubille hose clamp pipe leading to throttle body.(since TB clean was done 800km ago)
4) checked wastegate hose <-- not sure how to check wastegate properly
5) checked all other coolant,vacumm hoses for cracks and made sure they are securely in.
6) tighten idle speed screw <--originally the car came with it tigtened.
7) left car idling for 5mins with no a/c, another 5mins with a/c

8) went for drive. WOT (floored) on 2nd gear, produced 5psi around 5-6k rpm, then to 3rd WOT still producing 5psi, 4th then 5th, still on 5-6psi. <-- could this be the stock boost for PFL VR4s be 5psi?

Noticed that the boost responses better after 10km of spirited driving, could this be the ECU learning or relearning and adjusting the timing of the engine?

The car is performing better, but I'm still convinced its not yet back to its old responsiveness a week ago. I remembered the car not having any lag, it would respond to throttle pedal changes instantly.

Hoping the performance can improve as the kilometer builds, perhaps this sluggish performance is an adjustment of timing by the ecu due to the 95RON?

Will report back after another full tank of the 98 RON.

thanks for reading, I welcome any other suggestions

 

[sharky]

Hi. I think your base idle is screwed up. I had a similar issue with my car hesitating and generally bogging down on take off. My car is completely standard. I fixed mine by adjusting the base idle screw( it was wrongly fully closed) to get the correct factory idle rpm, I think it is 650+/-50 rpm. My screw is now set to about close to 1/2 open from full closed. I used evoscan to park the idle stepper motor and to monitor the step count at idle while doing the adjustment. Car is idling fine now and no more bogging or hesitation and very eager to rev.

 

[rooks]

thanks for the reply Mark, looks like the problem is the clutch after all, although not stalling on tests it is on its way out. It would slip on boost on 2nd and 3rd gear.

with the idle speed screw closed tight, the car is actually idling fine on 650rpm and hasn't stalled once perhaps the clean airfilter and ecu reset is what i missed when i changed the isc motor months ago.

can anyone else verify if the idle speed screw needs to be 1/2 opened from closed or fully closed?

cheers.

 

[sharky]

Sorry just to clarify, I meant to say my idle screw is unscrewed close to 1/2 turn from closed. I did not mean unscrew it 1/2 out. This all can be checked on Evoscan- very useful tool!

 

[matchtheclown]

Andrew,
I reckon you are unfortunately just getting used to the power.

No car feel as fast 6 months later as the first day or week you drove it.

I'm rather used to my much turned up boost with the fmic now. The first couple of days I was pretty bug eyed over it.