Engine surge

[stevesingo]

Well done. You need to get back to the rollers (the same ones) to check the improvements and have a Air/Fuel mixture curve done to see how it is running.

Steve

[Pentoman]

Cheers. The mixture at idle is spot on (set with the idle mixture adjuster). Interestingly it needed no adjustment after being put back together. I believe that this adjustment also forms the basis of the mixture throughout the rev range. So, theoretically if everything is in spec, the mixture should be correct up in the rev range too. However I'd like to get on a rolling road to confirm or deny this. I would also be very interested to see the new power curve.

Powerstation are my local, and where I had the previous run done. But while I'm sure they're great with Subarus, arrive in an H-reg Mercedes and they look at you as if you landed in a flying saucer and abducted a cow. I've never met their main chap (Dave?) though, perhaps he is better. It would be nice to have someone that is interested and at least knows the very basic concepts of the electro-mechanical system.

I have rarely ventured above 4000 rpm in the last few days - there's no need unless you really want to fly. I didn't think the engine had it in it!

I'd like to sort that lazy throttle response though. My estimations are that it takes between 0.5 - 1 second from hitting full throttle to getting full acceleration. It's like a decent modern turbocharged engine. Any guesses - rich? lean? no full throttle enrichment? fuel pressure? I'm feeling bullish having succesfully done the top end!

[Pentoman]

OK well after a while of driving, it's so much torquier low down. However the throttle response is still dreadful.

Let's say your on the motorway at 2500rpm in 5th gear and floor the throttle. There's plenty of acceleration available, but it takes 1-2 seconds to really arrive. It's not related to revs, but to how long you've held the throttle down for! My Dad's an experienced mechanic and also owned a 2.3 one of these many many years ago; he says it seems normal to him. But he's only driven it a couple of miles at low speeds....

I am mystified by this. I've spent most of this week (off work due to no water) checking every adjustment and electrical component, ignition timing and all test as per spec. Only fuel pressure I haven't checked.

The only thing that did any good was attaching a resistor in place of the coolant temperature sensor, to make the engine think it was 5 degrees Celsius. This seemed to cure the lame throttle response. Presumably it would be running rich in this situation? If so my cure seems to be to have more richness under load... The question is why!

Russell

[unclebenz]

This could be a huge long shot, but have a look at where the fuel supply line comes up to the fuel metering head. If it is secured with a banjo bolt, and it has a domed head, take it out and have a look for a tiny filter gauze within the bolt. If there is a gauze in there, dig it out and try the car without it in there.

(It is a HUGE long shot though...)

[Pentoman]

Unclebenz - thanks for the suggestion. I've heard a filter between the fuel supply line and metering head being discussed before on a Mercedes board, so it's interesting that you mention it. However I see no banjo bolt (I had to look that up!) on my car. The line coming from the fuel pump has a bolt around the end that hangs somewhat when disconnected, but can't come off. Then it tightens onto the fuel bits. I'll take a look though I don't remember seeing any filters there when disconnected.

Is it worth me checking differential pressure in the fuel distributor bit?

[unclebenz]

Some have the banjo bolt, you have the tube nut type, so not relavent to your car, sadly. Checking pressures would be a good idea. The pressure differential over the warm up regulator has a marked effect on mid and upper range fuelling. Stealth use this device to alter the mid and upper range fuelling when we convert golf 16vGTi's to two litre capacity.
I still feel the problem you have is with fuelling. A good rolling road session with gas analysis may find the mixture is too weak once off idle.

[Pentoman]

unclebenz said:

Some have the banjo bolt, you have the tube nut type, so not relavent to your car, sadly. Checking pressures would be a good idea. The pressure differential over the warm up regulator has a marked effect on mid and upper range fuelling. Stealth use this device to alter the mid and upper range fuelling when we convert golf 16vGTi's to two litre capacity.
I still feel the problem you have is with fuelling. A good rolling road session with gas analysis may find the mixture is too weak once off idle.

I agree with you, it can't be much more than fuelling but with so many factors affecting it (diff pressure, electrohydraulic actuators etc, plate alignment) how can you ever be confident what's going into the cylinders when you squeeze the throttle? Rolling road would be nice, but it's expensive and I don't really have the time or funds, I'd be more likely to sell the car. It would likely just confirm what I think - a lack of enrichment on initial throttle opening?

I have bought a 6 kOhm resistor which I'll use to fool the computer into thinking it's cold, and run like that for a while to see what happens. The increased richness seemed to improve things on a temporary test.

The bit about mods for 2.0 Golf GTi conversions is interesting.
It's frustrating because the car is not a dog and anyone else who drives it finds no problem, but I feel it there.

[Snake the Sniper]

Is there an uprated fuel pressure valve for your car? If so, it might be worth a punt as it sounds like the pressure's a bit down.

[Pentoman]

Snake the Sniper said:

Is there an uprated fuel pressure valve for your car? If so, it might be worth a punt as it sounds like the pressure's a bit down.

After fooling the injection computer into thinking the car was cold with a resistor, and discovering improved throttle response, I have adjusted the allen key adjustment on my EHA valve (the thing that varies pressure electrically). I did it after much consulting with a chap in NZ who's doing the same to his on a dyno.

Things are much much better now. Performance throughout is strong but most importantly the throttle response is sweet (or as sweet as it gets on K-jet) at any revs, no lag or surge feeling at all.

Not sure if anyone's interested, but to complete the thread I can post the results of the performance improvement from the rebuild.

This was my fastest run from before the rebuild:



You should ignore the 0-60 time - I didn't hit 60 in 2nd gear (it's touch and go whether you hit it in a cossie!). Instead pay attention to the 0-100 time.

After the rebuild, I did two runs (with a FULL tank of 95 RON too)




Best quarter mile time 15.6s
Best quarter mile speed 90.1 mph
None of the runs had *perfect* starts but they weren't dreadful either.
All runs done on the same stretch of (private!!) flat road, in the same direction from the same start point.

So it has certainly shaved 1.5s off the 0-100 mph, which isn't bad, considering the rebuild is more to address the low down torque than the top-end power. But the improved bottom end is the real news, much much better. These runs were from before my eha tweak so entirely attributable to the rebuild.

[Snake the Sniper]

Excellent, glad to hear it's now finally sorted to your satisfaction!

[Pentoman]

Well for anyone who's still reading, I've been tinkering with the adjustment on the EHA to change the mixture under load (this is a little electric actuator driven by the ECU to adjust the mixture by changing the differential pressure in the fuel distributor. I've no idea what I just typed!)

Through trial and error including going too-rich and inducing misfiring, then too lean and not being able to past 4000rpm, I've got it set a bit richer than it was. Throttle response is much better and there isn't the throttle lag there used to be - it's not too frustrating to drive any more! But it still doesn't pull that cleanly, it's worse than other petrol cars, and certainly worse than a decent carb engine. Monumentally disappointing given the lively drive you are expecting from a n/a cosworth twin-cam :/.