924Board.org

[Rick MacLaren]

Yes it could also be a missfire. This is a curious problem. I think MORE DESCRIPTION is needed.

Hesitation comes from either air, gas or electrics. I can see where Smoothie is coming from, as I had a wastegate prob. a year back, but this sounds different. Notably, being able to get to 5000 RPM cleanly in second. That is an anomoly. If the wastegate is stuck, you won't see 5000 RPM before your head blows off.

Smoothie...so you were able to get yours to 5000 RPM with the wastegate plunger stuck before any lurching???

HOW? The boost should have been up in the 2000 PSI range by then (exaggerating so you get the point), with a stuck plunger. The cutoff would kick in and there's no way you'd get to 5000 RPM without lurching all over the place on the way there.

That's why I'm not yet convinced it's the wastegate. Or it's the way he's described it, cause mine has all those symptoms and the wastegate is moving along fine.

I hope you're right Smoothie, but it still won't help my symptoms (cause the wastegate isn't stuck) and the hesitation still exists.

Remember the prev. posts..."I would suspect the overboost switch as well, but check your distributor rotor for buildup, and check the ignition timing. In my experience, the timing setting is very picky, and will misfire if set incorrectly. Best of luck."

When was the fuel filter last changed?
When was the popoff valve checked?
Air box checked?
Vaccuum lines all functioning ok?
Loose distributor?
Was it a new rotor, or a cleaned up one?
What octane gas is in there?


I'm going after my fuel filter next. Damned thing is $65 CDN.


[ This Message was edited by: Rick MacLaren on 2002-06-14 07:13 ]

[Smoothie]

I believe you can go to 5000 rpm and above with a malfunctioning wastgate without triggering the fuel cutoff. It's a long time since my car was in that condition and I can honestly say I don't remember every detail of how it performed then, but it should be easy to verify with a car that has a good (or bad) wastgate and a boost gauge. The wastegate does its' thing at about 8 psi. Just take it for a drive and accelerate gradually while being carefull not to exceed 8 psi (or any psi below the fuel cutoff psi). This simulates me driving around carefully with a blown wastegate diaphram years ago. You should find you can make it to 5000 or 6000 and beyond to the rpm cutoff. -Actually, of course you can. Don't even need to test it, but go ahead if you like.

[John H]

[Rick MacLaren]

I hear ya Smoothie - that's when it's stuck open, I guess I meant when it's stuck closed.

From what I remember, when it's stuck closed, the pressure built up very very quickly at even a 1/4" press of the pedal. Boost rose, no substantial increase. If I floored it, the boost went above 20 and at around 18 (+/-) the cutoff took effect.

The simulation for a stuck-closed one is, I think, to try to drive without letting the boost rise above 0.

Hey, could be the wastegate. Just from his description of how smooth it was in second, to 5000, it seemed either
(a) intermittent sticking of the wastegate in either up or down or
(b) it's sticking in the open position with the plunger up or
(c) something else.

Rick

[ This Message was edited by: Rick MacLaren on 2002-06-14 12:08 ]

[Smoothie]

Actually, the situation I was talking about was with the wastegate stuck closed. That's the condition you have when the diaphram is blown out and the spring is still good - when there's nothing to limit the boost except the fuel cutoff switch. With a smooth-gradual movement of the accelerator and not pressing down too far, you can keep the boost pressure from going too high and at the same time get into the higher rpms.

Did you try a new o2 sensor on your car Rick? You said your air:fuel was already checked, right?

[Rick MacLaren]

Yeah air/fuel came out fine on the initial tests. I disconnected the o2 but nothing substantial in the way of improvements yet. Tests begin again Wednesday. Leakdown, compression, and hooking in a fuel/air mixture gauge.

Damn.

Well I must be off base in my memory of the wastegate situation. But I can't figure out how this guy manages that trick you're talking about without looking at a boost gauge. If he floors it, it'll crap out fast with the fuel pump cutoff. So I'm not able to see how he can make the smooth rise to 5K RPM. Oh well. I'm not gonna fixate on it.

I give up!

I hope the guy gets it figured out.


[ This Message was edited by: Rick MacLaren on 2002-06-14 13:55 ]

[Smoothie]

Other than the wastegate and a bad plug wire connection, the only other problem I had with misfires or hesitation was caused by the connection to the DITC box. That was the first problem I came to this board with and I'm real glad to have found the answer. That one would have been driving me nuts to this day and cost me a few hundred wasted dollars too. It's only on '81-'82 931s with digital ignition timing control.

[John H]

Another cause of misfires is a faulty fuel pump.
If the pump is not running 100% at the higher rev's you can get a slight hestitation just like fouled plugs or faulty leads.


[ This Message was edited by: John H on 2002-06-14 14:38 ]

[Ants]

Hey guys
Thanx for all your help, cheers for the repair description John H, and Smoothie your right its like a violent lurch that throws you against the seat belt.
I know what you mean about the fuel pump too, not long after i bought it (1997) i had a hesitation at high revs under load (6000rpm) i had all new ignition wires then trying to solve it, then i replaced the fuel pump and hey presto sorted, but this is a different sort of hesitation, more like someone trying to push you through the windscreen.
It was serviced recently but the fuel filter wasn't changed cos they couldn't undo the bolts, it was last changed about 10,000 miles ago, so that something else i need to look into.

Oh and its the series 1 car so it doesn't have digital ignition or a chip???

Cheers

Ants

_________________
1980 931 Euro spec, "you know the one with the power, without repeaters or those daft bumper extensions."

[ This Message was edited by: Ants on 2002-06-14 18:30 ]

[Rick MacLaren]

I've got a Series 1 and I don't believe it has a chip or fully digital ignition.

[Smoothie]

Yeah, series 1 doesn't have digital ignition timing control. DITC includes a crank sensor on the flywheel, small black box behind the radio, no vacuum advance on the distributor, etc.

Due to the severe nature of your hesitation Ants, I have to up my 99% to a 100% sure that your wastegate is stuck closed -and I'm 99% sure it's because of a torn diaphram.

Wish I had as sure an answer to your problem, Rick. Just hang in there - we'll get it.

[numbers]

Well guys, I still think, it is just the wastegate. I did a few runs with mine, and I am getting 15 PSI max in second, but an getting 17 PSI in third. So, apparently you get more boost with more load. Maybe the engine can't take the air as fast when under load, allowing the turbo to build up more, or the exhaust gasses are hotter under load, spinning the turbo up faster. Anyway, I think Ants is just hitting the wall caused by the over-pressure switch cutting off fuel. Also, I believe that the max pressure that you will get out of the stage 1 turbo is about 20 to 21 PSI. When I first bought mine, it had a ton of power, but it also had a loud rattle under the hood. I traced the rattle to the pressure line going to the turbo. It was broken in two, down between the head and the firewall. After I fixed it, power was way down. So, who knows how long the PO had been running with no wastegate. I didn't have a boost guage back then, but I figure the max boost couldn't have been too high, as the engine is still running 17 years later.

[numbers]

Well guys, I still think, it is just the wastegate. I did a few runs with mine, and I am getting 15 PSI max in second, but an getting 17 PSI in third. So, apparently you get more boost with more load. Maybe the engine can't take the air as fast when under load, allowing the turbo to build up more, or the exhaust gasses are hotter under load, spinning the turbo up faster. Anyway, I think Ants is just hitting the wall caused by the over-pressure switch cutting off fuel. Also, I believe that the max pressure that you will get out of the stage 1 turbo is about 20 to 21 PSI. When I first bought mine, it had a ton of power, but it also had a loud rattle under the hood. I traced the rattle to the pressure line going to the turbo. It was broken in two, down between the head and the firewall. After I fixed it, power was way down. So, who knows how long the PO had been running with no wastegate. I didn't have a boost guage back then, but I figure the max boost couldn't have been too high, as the engine is still running 17 years later.

[Smoothie]

Good point - the pressure line. I think you meant to say "the pressure line to the wastegate", not "to the turbo" though. That would leave the wastegate shut just like a torn diaphram would. -Also, with a break in that pressure line your air:fuel ratio would be messed up because there would be a path for outside air after the fuel metering plate.

With the break in that line, did you get a loud rushing air sound under boost? -Actually, it was probably air rushing out of the line that caused it to rattle around.

[ This Message was edited by: smoothie on 2002-06-15 02:27 ]

[larso]

YES make sure it isn't your fuel pump. Bad fuel pumps can do the same thing...It gives you a literal whip lash...Just ground out the fuel cutoff switch ,drive it and see what happens. If it is a REALLY WEIRD intermittent problem, it could be the fuel pump.

It could also be air in fuel lines, or bad gas! Sludgy or crappy gas can work fine with not very much load...but once you rev it up and start flowing lots of gas, the fuel pump can't pump the bad gas, and the gas is all separated so cuts off you engine. When I drove my car to the last few drops of gas, the last few drops of gas were HORRIBLE, the car cut out at higher RPMS (even at 3000RPM) but was fine if I went to 2000RPM. The last few drops of gas in the tank is always crappy gas, it's never fresh, so I know for sure that bad gas and bad fuel pumps, and bad filters can cause these intermittent unexplainable problems.

Could be anything though, just try to solve it piece by piece by DELETING certain things by testing stuff out. Like the boost switch, easiest thing.

I feel as if all my advice on this forum relates to bad gas. I am obsessive about it, But, I swear with my right hand over my heart, that it is what causes the weirdest, problems...and it is the reason for many problems with these cars, since previous owners leave them sitting. Hondas do not sit like these 924s. so hondas never have bad gas. That's why fuel distributors go bad in these cars, the bad gas causes it! I know I know, I'm obsessive, but the most problems I''ve ever solved on a 924's engine have related to bad gas! Especially that STINK!!!

[ This Message was edited by: larso on 2002-06-19 18:53 ]