Diagnostic log of high rev miss
Discussion
I decided today to have a look at what might be causing the high end miss that i have never quite gotten rid of. The car has had a new coil, leads and plugs, crank sensor removed and cleaned, fuel filter replaced, throttles balanced. Every thing has improved it or pushed it up the rev range but nothing has sorted it totally.
Below is the log of a run from stationary, 1st, 2nd and then 3rd with the throttle flat, finally changing into 4th. The miss starts at 6k, the zig zag in the speed line (red) is down 500rpm then back up and takes place in 0.2 of a second which i dont see as possible, so may be a bad reading from the position sensor, however what concerns me is the lambda reading.
It takes a plunge at 6k where it starts to miss, Im aware that this is not monitored by the ecu as such but it still means its going lean, to what extent i dont know and wont until i can get my wideband sensor on there.
Being pretty much the same on both banks, its leading me to suspect the fuel pump as there is little else that shared by both banks.
Just thought i would share, any comments welcome.
Below is the log of a run from stationary, 1st, 2nd and then 3rd with the throttle flat, finally changing into 4th. The miss starts at 6k, the zig zag in the speed line (red) is down 500rpm then back up and takes place in 0.2 of a second which i dont see as possible, so may be a bad reading from the position sensor, however what concerns me is the lambda reading.
It takes a plunge at 6k where it starts to miss, Im aware that this is not monitored by the ecu as such but it still means its going lean, to what extent i dont know and wont until i can get my wideband sensor on there.
Being pretty much the same on both banks, its leading me to suspect the fuel pump as there is little else that shared by both banks.
Just thought i would share, any comments welcome.
prior to my engine rebuild, i had similar symptoms, i.e. a high revs misfire, that you could run past, but it was a stutter all the same.
Since my engine rebuild, i now have a stutter at low revs and light throttle!! It was fine for a while but has been evident in the last couple of drives.
I had thought the rough running was perhaps due to a known problem with the alternator belt slipping, but have replaced alternator and belt. I now have to go through a similar diagnosis i guess, finding whats causing. I have been advised by the engine builder to drive it for a while until the problem becomes more readily evident, as these things are so difficult to track down.
Ever had it mapped or tried a different map / fuelling chip as per TVR powers decat chip? May be worth asking Dom if you can try one to see if it solves your problem?
Since my engine rebuild, i now have a stutter at low revs and light throttle!! It was fine for a while but has been evident in the last couple of drives.
I had thought the rough running was perhaps due to a known problem with the alternator belt slipping, but have replaced alternator and belt. I now have to go through a similar diagnosis i guess, finding whats causing. I have been advised by the engine builder to drive it for a while until the problem becomes more readily evident, as these things are so difficult to track down.
Ever had it mapped or tried a different map / fuelling chip as per TVR powers decat chip? May be worth asking Dom if you can try one to see if it solves your problem?
I spoke to Dom a while ago about it, he was very helpfull but was at abit of a loss with it and said it sounded like the ecu could be faulty and to see if I could borrow one to try but im not sure. He did say he would send one of his chips, (the dethrottle) but this never turned up and i felt cheeky chasing it as i was not paying for it (unless it cured the problem).
Mine is a 2000 car and i exect the throttles may be worn, i was expecting to see on the log the throttle position giving shaky readings but they actually look pretty good, im planning of fitting bearings to the throttles in the next few weeks, but seeing the log somethink is causing a loss of fuel.
Mine is a 2000 car and i exect the throttles may be worn, i was expecting to see on the log the throttle position giving shaky readings but they actually look pretty good, im planning of fitting bearings to the throttles in the next few weeks, but seeing the log somethink is causing a loss of fuel.
Bearings in the throttle bodies are something i have been considering too, just to eliminate that one once and for all!!
edited the original text cause i have read around and it seems Chad Speed has already done this and recommend some bearings. So, my only question is the cutter size to get a nice press fit in the body housing? Whats your intention BGB?
edited the original text cause i have read around and it seems Chad Speed has already done this and recommend some bearings. So, my only question is the cutter size to get a nice press fit in the body housing? Whats your intention BGB?
Edited by Robertjp on Tuesday 5th January 10:38
I am in Hampshire, and your welcome to try my blue mbe ecu if you like. Have a decat chip in at mo from power.
Is it possible although I think not that a pipe is collapsing somewhere at those rpm causing a starvation before returning to pressure? Know turbo intakes can colapse. Our SP6 are solid airboxes I know, so unless it was the hose feeding into the bottom I'm not sure.
Changing my lambda certainly made a difference to smooth running. Also the plugs are the same I take it, maybe go with a colder plug?
Is it possible although I think not that a pipe is collapsing somewhere at those rpm causing a starvation before returning to pressure? Know turbo intakes can colapse. Our SP6 are solid airboxes I know, so unless it was the hose feeding into the bottom I'm not sure.
Changing my lambda certainly made a difference to smooth running. Also the plugs are the same I take it, maybe go with a colder plug?
Robertjp - Im toying with this at the moment. Will be using a custom end mill will a presision ground pilot to centralise it or set up in a lathe and bore each one to take the bearing. I wont know which untl I get them off and apart. I may use different sized bearings yet so t is less machining needed, but i will report back with what i find.
Justyr - The filter has been done, the pump sounds ok, but before I replace it I think im going to check the intank pickup and make sure thats not covered in crap!
Tuscan al - thanks for the offer, that would be excellent but sadly im in Lincoln so a good trek from you. I would be happy to pay for special delivery each way if you would be willing to send it or I could send you mine if you would be wiling to try it on your car?
Plugs are new and the standard recommended, car drives smoothly otherwise (Above 4k the ecu does not the use o2 sensor so they are not he cause of the miss. I replaced 1 o2 when i got the car as when the engine mount was cracked it looked like the sensor hit the chassis and snapped it in two. Guy had run it like this with the ecu fault warning showing.
Justyr - The filter has been done, the pump sounds ok, but before I replace it I think im going to check the intank pickup and make sure thats not covered in crap!
Tuscan al - thanks for the offer, that would be excellent but sadly im in Lincoln so a good trek from you. I would be happy to pay for special delivery each way if you would be willing to send it or I could send you mine if you would be wiling to try it on your car?
Plugs are new and the standard recommended, car drives smoothly otherwise (Above 4k the ecu does not the use o2 sensor so they are not he cause of the miss. I replaced 1 o2 when i got the car as when the engine mount was cracked it looked like the sensor hit the chassis and snapped it in two. Guy had run it like this with the ecu fault warning showing.
Edited by BGB autosport on Tuesday 5th January 13:42
BGB, knowing what i do now about the worn throttle bodies the symptoms you describe are consistant with them being the cause.
I have been told that due to vibration at high revs (6k rpm + )the throttle pots go into overdrive and as a result the ECU can momentarily stall or even shut doen the ignition system, which would effectively cuts the fuel and you would get instant lean mixute that would be evident in the lambdas... as your seeing...
Hope that helps! I have just ordered mine from Racing Green, £275 for the upgraded roller bearing set, i couldnt get it done myself for cheaper.
I have been told that due to vibration at high revs (6k rpm + )the throttle pots go into overdrive and as a result the ECU can momentarily stall or even shut doen the ignition system, which would effectively cuts the fuel and you would get instant lean mixute that would be evident in the lambdas... as your seeing...
Hope that helps! I have just ordered mine from Racing Green, £275 for the upgraded roller bearing set, i couldnt get it done myself for cheaper.
Edited by Robertjp on Wednesday 13th January 13:19
Rob, i saw your other thread about the ecu going mental and it certainly sounds like it could be the answer. Im hoping to get the bearings done in the next few weeks so will soon see. Using the best roller bearings its looking like the cost will be in around £40 plus my time removing, machining and refitting.
BGB, I'd be interested to know what parts you are using as I have access to a CNC mill (well my dad does!) and it might be worthwhile getting mine done if it's that cheap in spare bits (ie bearings). Can you also post up a short guide on the process if possible please? I've had my Tusc since Nov 05 (20k miles) and it's now on over 55k miles without any work on the throttle bodies.
Edited by S6PNJ on Wednesday 13th January 20:17
Robertjp said:
Hope that helps! I have just ordered mine from Racing Green, £275 for the upgraded roller bearing set, i couldnt get it done myself for cheaper.
Could you give us more info on the throttle bodies from RG. Is this an exchange price for modified units? I can only see the later spec castings with the machining for bushes on their website.Basil Brush said:
Robertjp said:
Hope that helps! I have just ordered mine from Racing Green, £275 for the upgraded roller bearing set, i couldnt get it done myself for cheaper.
Could you give us more info on the throttle bodies from RG. Is this an exchange price for modified units? I can only see the later spec castings with the machining for bushes on their website.
Robertjp said:
Basil Brush said:
Robertjp said:
Hope that helps! I have just ordered mine from Racing Green, £275 for the upgraded roller bearing set, i couldnt get it done myself for cheaper.
Could you give us more info on the throttle bodies from RG. Is this an exchange price for modified units? I can only see the later spec castings with the machining for bushes on their website.high52kojak said:
BGB, knowing your previous ability on a lathe/mill I sure hope you let someone skilled in the art of machining do it!
Thats rich scrap boy, Siemens binned you because you were crap, Rolls took you on but then took you off the machines and put you in the office and now they have seen the opertunity to stop further out sourcing to Germany and sent you there to f
k them up to keep the work in the UK 
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