Discussion
What is engine "surge"? I feel like my Merc 190 2.5-16v's engine is doing it - if it is what I think it is. I think it's when you're on full throttle, and the engine is making lots of noise, but you're not really accelerating as much as you think you should be. Sort of like bogging down?
The car has great performance from 4,000rpm, enough to keep up with some pretty rapid modern machinery, and it even feels strong enough around town under 2,500rpm. But it's in-between these revs that it really kills me - i.e. exactly where you find yourself in day to day driving! It just feels so utterly... flat. Unwilling. Very soft throttle response. It vibrates, shakes and roars (it's comical that the Mercedes engine is apparently the most refined of the M3/Sierra cosworth/Mercedes cosworth trio..) but without really going anywhere. I'm sure it's off-cam but it feels worse than that. I often expect to open the bonnet and find a thick ball of socks lodged in the air intake preventing it from breathing properly..
It feels like I spend all day driving in one huge 1,000 rpm-wide flat spot. There's a marked increase in intake noise from 3,000 rpm, but it's not met by an increase in acceleration. In fact it's almost as if the whole thing slows down between 3,000 - 4,000 rpm!
Please help because it's ruining my enjoyment of a car which I was initially very excited to be buying (it's my first performance car), but I'm finding increasingly frustrating - it's a bit like driving a turbo car and falling off-boost every time you change gear.
The extra frustrating thing is that my dad runs a garage and so I have access to plenty of equipment and quasi-free labour (I still have to pay in other ways so it's not really free!) so, theoretically, fixing it shouldn't be a major issue if it is a problem in the first place. But parts are still expensive if you replace them willy-nilly, and my dad's not keen to get into heavy diagnostics on it, especially as he wouldn't make any money off me.... Plus he thinks he left all that behind in the '90s and can just use his laptop now
.
We did hook it up to a diagnostic machine:
The car has great performance from 4,000rpm, enough to keep up with some pretty rapid modern machinery, and it even feels strong enough around town under 2,500rpm. But it's in-between these revs that it really kills me - i.e. exactly where you find yourself in day to day driving! It just feels so utterly... flat. Unwilling. Very soft throttle response. It vibrates, shakes and roars (it's comical that the Mercedes engine is apparently the most refined of the M3/Sierra cosworth/Mercedes cosworth trio..) but without really going anywhere. I'm sure it's off-cam but it feels worse than that. I often expect to open the bonnet and find a thick ball of socks lodged in the air intake preventing it from breathing properly..
It feels like I spend all day driving in one huge 1,000 rpm-wide flat spot. There's a marked increase in intake noise from 3,000 rpm, but it's not met by an increase in acceleration. In fact it's almost as if the whole thing slows down between 3,000 - 4,000 rpm!
Please help because it's ruining my enjoyment of a car which I was initially very excited to be buying (it's my first performance car), but I'm finding increasingly frustrating - it's a bit like driving a turbo car and falling off-boost every time you change gear.
The extra frustrating thing is that my dad runs a garage and so I have access to plenty of equipment and quasi-free labour (I still have to pay in other ways so it's not really free!) so, theoretically, fixing it shouldn't be a major issue if it is a problem in the first place. But parts are still expensive if you replace them willy-nilly, and my dad's not keen to get into heavy diagnostics on it, especially as he wouldn't make any money off me.... Plus he thinks he left all that behind in the '90s and can just use his laptop now
. We did hook it up to a diagnostic machine:
pentoman said:
Hmm I'm pretty certain it's not a misfire, I know how a misfire feels and this definitely isn't misfire. Mechanic didn't reckon it misfired either.
A misfire would cause vibration, noise and loss of power. You have vibration, noise and loss of power. If it isn't a misfire, what is it?
I'm feeling guilty so am back grovelling..
I may have been a little harsh. Driving the car a bit more, it's really not that bad. I had spent the weekend driving my family's cars (90bhp golf tdi, Audi 2.5 V6 tdi, Golf 1.6S) all of which are more modern, and two of which are turbodiesels even if the Golf is a crummy old one.
BUT there is definitely a flat spot smack in the middle of the rev range and the throttle response is very soft. I feel that a cosworth n/a 16v should be a pretty sweet engine, but the best I can say about mine is its 'effective'.
I tried STP injector cleaner but it made no significant difference (a bit hopeful perhaps?!). I was thinking that if fuel pressure was low it would affect outright performance and top end, but top end is fine? I will test it though, it should be 5.8 bar IIRC.
Here's some extra info to throw into the mix.. the rolling road graph
Check out that yummy flat spot.
By the way I am no expert but am told that first pic I posted is telling me cylinders 1 and 3 are comparatively weak. I as hoping some kindly knowledgeable fellow would opine on this for me. BTW Here's what I believe those 7 graphs mean:
From top-left:
1 secondary (spark?) voltage?
2 primary spark voltage?
3 Combustion time per cylinder in ms
Second row:
4 RPM drop caused by each cylinder being shut off
5 Idle stabilisation test while each cylinder is shut off
6 Compression per cylinder, measured in Amps required by starter to turn each cylinder through combustion stroke
Third row
7 Change in HC output for each cylinder that is cut out.
I may have been a little harsh. Driving the car a bit more, it's really not that bad. I had spent the weekend driving my family's cars (90bhp golf tdi, Audi 2.5 V6 tdi, Golf 1.6S) all of which are more modern, and two of which are turbodiesels even if the Golf is a crummy old one.
BUT there is definitely a flat spot smack in the middle of the rev range and the throttle response is very soft. I feel that a cosworth n/a 16v should be a pretty sweet engine, but the best I can say about mine is its 'effective'.
350matt said:
Sounds like lack of fuel, whats the fuel pressure at the rail?
Bottle of injector cleaner perhaps? along with a new fuel filter?
Matt
Bottle of injector cleaner perhaps? along with a new fuel filter?
Matt
I tried STP injector cleaner but it made no significant difference (a bit hopeful perhaps?!). I was thinking that if fuel pressure was low it would affect outright performance and top end, but top end is fine? I will test it though, it should be 5.8 bar IIRC.
Here's some extra info to throw into the mix.. the rolling road graph
Check out that yummy flat spot.
By the way I am no expert but am told that first pic I posted is telling me cylinders 1 and 3 are comparatively weak. I as hoping some kindly knowledgeable fellow would opine on this for me. BTW Here's what I believe those 7 graphs mean:
From top-left:
1 secondary (spark?) voltage?
2 primary spark voltage?
3 Combustion time per cylinder in ms
Second row:
4 RPM drop caused by each cylinder being shut off
5 Idle stabilisation test while each cylinder is shut off
6 Compression per cylinder, measured in Amps required by starter to turn each cylinder through combustion stroke
Third row
7 Change in HC output for each cylinder that is cut out.
kirsty5150 said:
I'd be tempted to look into the differences between the relative compressions. They should all be much closer than that. Rings on the way out perhaps?
Thanks... we did some sort of test that determines where the pressure is being lost. There was no hissing through the oil filler so I don't think it's the piston rings. I think its the top end - it's not uncommon to rebuild the top end at ~100k miles on these.
My question though is: would rebuilding the top end cure the mid-range flat spot and weak throttle response? The throttle response in the flat spot is such that when you initially squeeze the throttle, the engine momentarily loses power, i.e. acceleration decreases initially, but then it picks up and accelerates properly. It's not dreadful but enough to feel like you're driving a turbo car - but without all the torque! Could poor compression cause that?
please help, thanks!
That Daddy said:
Would i be right in saying this car as Bosch constant injection,metering head with lots of pipes coming out etc.
Yes, sadly - A tedious mix of old fashioned complex mechanical parts, combined with computers and sensors to go wrong, giving you the worst of both worlds...
Please continue..! This flat spot and "negative" throttle response are even noticeable from the passenger seat, only from 3000-4000.
Edited by pentoman on Tuesday 15th May 10:24
It might be worth having a look at the top end, you might get away with re-seating/re-grinding the valves. Otherwise it seems the mixture is going all to pot at the the flat spot. Have you got a TPS or similar on the engine? If so, has it been changed recently, as they tend to wear in the most used postions, ie mid throttle/mid revs place. This then totally messes with the fueling as the engine has no idea what it's doing. Or if not the TPS, then something similar is poorly. MAF perhaps? I don't know what inlet sesnor you have, but it may be whatever you have.
kirsty5150 said:
It might be worth having a look at the top end, you might get away with re-seating/re-grinding the valves. Otherwise it seems the mixture is going all to pot at the the flat spot. Have you got a TPS or similar on the engine? If so, has it been changed recently, as they tend to wear in the most used postions, ie mid throttle/mid revs place. This then totally messes with the fueling as the engine has no idea what it's doing. Or if not the TPS, then something similar is poorly. MAF perhaps? I don't know what inlet sesnor you have, but it may be whatever you have.
Update.. yesterday I ran the (really old fashioned!) fault diagnosis. This indicated no faults, so that gives me some confidence in the sensors etc. I was hoping one of them would be failed...
Yes there is a moving-plate type air flow meter. I have hooked up a multimeter to this and watched the resistance as it changes throughout the deflection of the plate. It seemed consistent and there were no wild fluctuations or infinite/zero resistance points. So I'm fairly confident that's working ok? They're expensive too. :/ That's the only intake air pressure/volume sensor that there is, there's no TPS.
My dad has suggestion removing the fuel distributor and cleaning it (he has an ultrasonic cleaner)?
Edited by pentoman on Wednesday 16th May 11:39
What fuel does the manual state should be used and what are you using and what adjustments need to be made for different fuel grades?
Putting super U/L in when you should be using regular will have an detrimental effect on performance.
What compression ratio does the engine have?
What controls the ignition advance curve?
Is there a vacuum unit on the distributor, if not where is the vacuum line for the ignition advance and what condition is it in?
Can you carry out a "proper" compression test and a leakdown test?
Check all of the hoses and vacuum lines first
Steve
Putting super U/L in when you should be using regular will have an detrimental effect on performance.
What compression ratio does the engine have?
What controls the ignition advance curve?
Is there a vacuum unit on the distributor, if not where is the vacuum line for the ignition advance and what condition is it in?
Can you carry out a "proper" compression test and a leakdown test?
Check all of the hoses and vacuum lines first
Steve
If nothing wrong is indicated- it could simply be a characteristic of the torque curve/volumetric efficiency curve. There region where it is indicated on the graph is the region where exhaust tuning still predominates- probably just after the four tuned length- it could just be an "anti scavenging region" where the gas dynamics are working against the cam timing and overlap in the cylinder.
Have you driven another same spec 190E cosworth to see if this car experiences this phenomenon too?
Have you driven another same spec 190E cosworth to see if this car experiences this phenomenon too?
Thankyou steve, i'll try to answer what I can
There's a nob under the bonnet you turn if you are using lower grade fuel. Instruction manual states the standard 'S' position is for premium 95RON fuel. This is the highest position it goes - the engine makes no provision for 97/98 super unleaded.
What compression ratio does the engine have?
I believe it's 9.7:1 standard but don't know for sure. I know it's less now....!
What controls the ignition advance curve?
There's a separate ignition computer which reads vacuum, engine temperature and some other stuff. I have a spare which I plan to try out.
Is there a vacuum unit on the distributor, if not where is the vacuum line for the ignition advance and what condition is it in?
I don't think there's a vacuum unit on the distributor but will check, thanks for the idea. Vacuum goes to the above computer (as well as to everything else in the entire car by the looks of things!!). I'm told the distributor is just used for distribution of the spark and can't be used to advance/retard ignition. All vacuum lines were replaced 3 years ago and all looks well on a cursory glance.
Can you carry out a "proper" compression test and a leakdown test?
Yep already have a few months back, these were the numbers, from front to back:
120
155
120
110
Most leak sounded to be coming from the exhaust and intake rather than the oil cap - suggesting top end work needed?
Check all of the hoses and vacuum lines first
How do i check them? Just visual? I listen for hissing, but because it's a noisy engine you can't hear a lot with it running.
I've driven 1 (recently rebuilt) 2.5-16 and was looking specifically for this flat spot - it didn't seem to be present. The characteristic on my example is bad enough to make me want a different car! It's not like being off cam, it's worse than that because of the inverse throttle response.
I've found some dyno sheets from other 16v cars (but not a standard 2.5-16 unfortunately) and they do all exhibit this symptom a little:
^ This is a US spec (slightly less power) 2.3-16 with 'sport cams'. Not really fair I know.
^ This is an Evolution 1 model - which has a short stroke version of the 2.5-16 engine but identical 200bhp output. I would speculate being a higher revving short stroke engine, any low-mid range flat spot would be worse?
Neither seem to exhibit quite the pronounced dip as my car but it is slightly characteristic.
The suggestion is still nagging me, from a professional engine builder guy on a Mercedes forum I frequent, who does a lot of work on these engines (he himself has a 400bhp+ turbo 2.5-16), and maintains that it's almost certainly due to timing chain stretch...?
stevesingo said:
What fuel does the manual state should be used and what are you using and what adjustments need to be made for different fuel grades?
Putting super U/L in when you should be using regular will have an detrimental effect on performance.
Putting super U/L in when you should be using regular will have an detrimental effect on performance.
There's a nob under the bonnet you turn if you are using lower grade fuel. Instruction manual states the standard 'S' position is for premium 95RON fuel. This is the highest position it goes - the engine makes no provision for 97/98 super unleaded.
stevesingo said:
What compression ratio does the engine have?
I believe it's 9.7:1 standard but don't know for sure. I know it's less now....!
stevesingo said:
What controls the ignition advance curve?
There's a separate ignition computer which reads vacuum, engine temperature and some other stuff. I have a spare which I plan to try out.
stevesingo said:
Is there a vacuum unit on the distributor, if not where is the vacuum line for the ignition advance and what condition is it in?
I don't think there's a vacuum unit on the distributor but will check, thanks for the idea. Vacuum goes to the above computer (as well as to everything else in the entire car by the looks of things!!). I'm told the distributor is just used for distribution of the spark and can't be used to advance/retard ignition. All vacuum lines were replaced 3 years ago and all looks well on a cursory glance.
stevesingo said:
Can you carry out a "proper" compression test and a leakdown test?
Yep already have a few months back, these were the numbers, from front to back:
120
155
120
110
Most leak sounded to be coming from the exhaust and intake rather than the oil cap - suggesting top end work needed?
stevesingo said:
Check all of the hoses and vacuum lines first
How do i check them? Just visual? I listen for hissing, but because it's a noisy engine you can't hear a lot with it running.
Marquis_Rex said:
If nothing wrong is indicated- it could simply be a characteristic of the torque curve/volumetric efficiency curve. There region where it is indicated on the graph is the region where exhaust tuning still predominates- probably just after the four tuned length- it could just be an "anti scavenging region" where the gas dynamics are working against the cam timing and overlap in the cylinder.
Have you driven another same spec 190E cosworth to see if this car experiences this phenomenon too?
Have you driven another same spec 190E cosworth to see if this car experiences this phenomenon too?
I've driven 1 (recently rebuilt) 2.5-16 and was looking specifically for this flat spot - it didn't seem to be present. The characteristic on my example is bad enough to make me want a different car! It's not like being off cam, it's worse than that because of the inverse throttle response.
I've found some dyno sheets from other 16v cars (but not a standard 2.5-16 unfortunately) and they do all exhibit this symptom a little:
^ This is a US spec (slightly less power) 2.3-16 with 'sport cams'. Not really fair I know.
^ This is an Evolution 1 model - which has a short stroke version of the 2.5-16 engine but identical 200bhp output. I would speculate being a higher revving short stroke engine, any low-mid range flat spot would be worse?
Neither seem to exhibit quite the pronounced dip as my car but it is slightly characteristic.
The suggestion is still nagging me, from a professional engine builder guy on a Mercedes forum I frequent, who does a lot of work on these engines (he himself has a 400bhp+ turbo 2.5-16), and maintains that it's almost certainly due to timing chain stretch...?
Edited by pentoman on Monday 21st May 11:47
Could be chain stretch throwing the cam timing out, thus causing the flat spot, and less power than may otherwise be expected. It may well be worth changing it anyway, as you may not notice any noise or small amounts of slack in the chain if you inspect it. Is it an expensive job? If not, they should be changed every now and then, just much less often than belts.
pentoman said:
Thankyou steve, i'll try to answer what I can
stevesingo said:
What fuel does the manual state should be used and what are you using and what adjustments need to be made for different fuel grades?
Putting super U/L in when you should be using regular will have an detrimental effect on performance.
Putting super U/L in when you should be using regular will have an detrimental effect on performance.
pentoman said:
There is a nob under the bonnet you turn if you are using lower grade fuel. Instruction manual states the standard 'S' position is for premium 95RON fuel. This is the highest position it goes - the engine makes no provision for 97/98 super unleaded.
Only use 95 fuel, no matter how tempting it may seem to use these "better" fuels.
stevesingo said:
What compression ratio does the engine have?
pentoman said:
I believe it's 9.7:1 standard but don't know for sure. I know it's less now....!
This backs up the above statement regarding fuel octane. Your CR will not be any less now, only your pressure is leaking away through worn parts.
stevesingo said:
What controls the ignition advance curve?
pentoman said:
There's a separate ignition computer which reads vacuum, engine temperature and some other stuff. I have a spare which I plan to try out.
stevesingo said:
Is there a vacuum unit on the distributor, if not where is the vacuum line for the ignition advance and what condition is it in?
pentoman said:
I don't think there's a vacuum unit on the distributor but will check, thanks for the idea. Vacuum goes to the above computer (as well as to everything else in the entire car by the looks of things!!). I'm told the distributor is just used for distribution of the spark and can't be used to advance/retard ignition. All vacuum lines were replaced 3 years ago and all looks well on a cursory glance.
Give all of the hoses connected with the injection and the inlet manifold a good going over, looking for any possible leak paths. Any air leak may cause a weak mixture.
stevesingo said:
Can you carry out a "proper" compression test and a leakdown test?
pentoman said:
Yep already have a few months back, these were the numbers, from front to back:
120
155
120
110
Most leak sounded to be coming from the exhaust and intake rather than the oil cap - suggesting top end work needed?
120
155
120
110
Most leak sounded to be coming from the exhaust and intake rather than the oil cap - suggesting top end work needed?
Can you get a leakdown test done? This will indicate as to where the pressure is going.
The suggestion is still nagging me, from a professional engine builder guy on a Mercedes forum I frequent, who does a lot of work on these engines (he himself has a 400bhp+ turbo 2.5-16), and maintains that it's almost certainly due to timing chain stretch...?
Timing chains don't stretch, they wear. The distance between the centres remains the same, the rollers wear. The effect is the same though, retarded cam timing and if this engine has done a few miles and not been looked after in the past (I'm sure you do), then it would be a likly possibility.
Steve
Super unleaded will not do anything, period! On a four valve per cylinder DOHC engine with a pent roof combustion camber and central spark plug the combustion process is very efficient. These types of engines will stand very high compression ratios (11:1 and more). This is because the mixture is inherently well mixed due to the tumble caused by the typically steep inlet ports these types of engines have, also the mixture is helped by the squish area which is also favourable in these types of engines. The mixture is ignited centrally in a geometrically symmetrical combustion chamber, and all of this means that the flame front progresses evenly, avoiding pre ignition better than almost all other types of engine.
The other main factors (temperatures & Boost pressure aside)in pre ignition is compression ratio, ignition advance and fuel octane. A higher compression will require less advance and/or higher octane to keep the flame front under control. It therefore stands to reason that if you have an efficient combustion chamber you can stand a higher compression ratio for a given fuel octane. The ignition timing is only set to get the best from the factors mentioned above.
So your 9.7:1 on a good combustion chamber will not require a high octane fuel. In fact, the ignition advance curve will have been devised for 95RON (or possibly lower, depending on the markets where the engine was sold), using a 97/98RON fuel (that effectively burns slower) will have a similar effect to retarding the ignition, you will loose power. Even if you re-mapped the ignition for the 97/98RON I doubt you would gain anything.
If you look at some modern high performance engines, they run 11:1 plus on 95 RON (my old civic type r was just this).
Hope this makes sense (and it is correct, or I'll be toast on here :-))
Steve
P.S. My E30 M3 had two fuel octane settings, one for 95 and one for 97RON. It ran best on the 97 setting on 95 fuel, with no pre ignition or pinking. That demonstrates how conservative the ignition maps can be. That is not to say yours is as conservative!!
The other main factors (temperatures & Boost pressure aside)in pre ignition is compression ratio, ignition advance and fuel octane. A higher compression will require less advance and/or higher octane to keep the flame front under control. It therefore stands to reason that if you have an efficient combustion chamber you can stand a higher compression ratio for a given fuel octane. The ignition timing is only set to get the best from the factors mentioned above.
So your 9.7:1 on a good combustion chamber will not require a high octane fuel. In fact, the ignition advance curve will have been devised for 95RON (or possibly lower, depending on the markets where the engine was sold), using a 97/98RON fuel (that effectively burns slower) will have a similar effect to retarding the ignition, you will loose power. Even if you re-mapped the ignition for the 97/98RON I doubt you would gain anything.
If you look at some modern high performance engines, they run 11:1 plus on 95 RON (my old civic type r was just this).
Hope this makes sense (and it is correct, or I'll be toast on here :-))
Steve
P.S. My E30 M3 had two fuel octane settings, one for 95 and one for 97RON. It ran best on the 97 setting on 95 fuel, with no pre ignition or pinking. That demonstrates how conservative the ignition maps can be. That is not to say yours is as conservative!!
Gassing Station | Engines & Drivetrain | Top of Page | What's New | My Stuff