Lambdas just wont do bugger all....
Discussion
I've been struggling with getting the car to run well at all for quite some time now (all f
king summer!). An obscure fault that was causing all of the sensor readings to jump about when the engine was started was eventually sorted when I discovered that TVR, in their infinite wisdom, decided to use a shared earth for the lambda heaters and the lambda sensors themselves, thus resulting in the possibility for the lambda power supply to affect the ecu earth loop. This was solved, or rather the symptoms of this fault were cured by running a direct earth from the lambda heaters to the engine block. I was hoping at this point that I would have a fully working engine. Who was I kidding? Everything seems fine now on the diagnostics, except that I get a very low voltage on the lambda sensors on startup- manages to creep up to creep up to about 0.15V on either sensor, then just about the time the lambdas should really be working (after about 60 sec.) they both fall down to a 0-0.1V. In addition, I get an AFR fault on both banks as the ecu maxes out on fuel enrichment. So clearly the ecu is seeing that the lambdas are showing a leam mixture, but whatever it does to try to enrich, the lambda values stay as if the engine is lean.
My first thought was that the lambdas were buggered. So, 2 brand new Bosch lambdas fitted. Still No change.
Second thought was that the ecu was faulty. So, ecu sent to TVR Power where they kindly tested it in two of their cars and found it to be working fine (thanks again to Dom).
Last head scratching though was that there was still something in the wiring between the sensors and the ecu that is causing interference. All wiring looked like and tested (on a multi-meter) like it checked out. However, to rule it out for good, I ran a brand new separate signal and earth direct from the lambda sensor to the ecu and ecu ground points respectivly. This wiring totally bypasses and isolates the original wiring. Result? Exactly the fking same as before.
Where else can I possibly go now?
I'm about to miss out on a big driving holiday because of this too. Sadly, I'm in Aberdeen so there's nobody remotly nearby that really knows TVRs. I guess I might have to eventually bite the bullet and get a transporter to take the car down south to a main dealer.
The gods of TVR just aren't with me this year.
king summer!). An obscure fault that was causing all of the sensor readings to jump about when the engine was started was eventually sorted when I discovered that TVR, in their infinite wisdom, decided to use a shared earth for the lambda heaters and the lambda sensors themselves, thus resulting in the possibility for the lambda power supply to affect the ecu earth loop. This was solved, or rather the symptoms of this fault were cured by running a direct earth from the lambda heaters to the engine block. I was hoping at this point that I would have a fully working engine. Who was I kidding? Everything seems fine now on the diagnostics, except that I get a very low voltage on the lambda sensors on startup- manages to creep up to creep up to about 0.15V on either sensor, then just about the time the lambdas should really be working (after about 60 sec.) they both fall down to a 0-0.1V. In addition, I get an AFR fault on both banks as the ecu maxes out on fuel enrichment. So clearly the ecu is seeing that the lambdas are showing a leam mixture, but whatever it does to try to enrich, the lambda values stay as if the engine is lean.My first thought was that the lambdas were buggered. So, 2 brand new Bosch lambdas fitted. Still No change.
Second thought was that the ecu was faulty. So, ecu sent to TVR Power where they kindly tested it in two of their cars and found it to be working fine (thanks again to Dom).
Last head scratching though was that there was still something in the wiring between the sensors and the ecu that is causing interference. All wiring looked like and tested (on a multi-meter) like it checked out. However, to rule it out for good, I ran a brand new separate signal and earth direct from the lambda sensor to the ecu and ecu ground points respectivly. This wiring totally bypasses and isolates the original wiring. Result? Exactly the f
king same as before.Where else can I possibly go now?
I'm about to miss out on a big driving holiday because of this too. Sadly, I'm in Aberdeen so there's nobody remotly nearby that really knows TVRs. I guess I might have to eventually bite the bullet and get a transporter to take the car down south to a main dealer.
The gods of TVR just aren't with me this year.
Oh, but I took it from the word enrichment that you used that the adaptives go +ve to try and throw more and more fuel in. The lambdas go to a high voltage when rich...so that also points to a massively lean mixture if they are always low...?
It sounds like you've thoroughly exhausted the electrical angle, so there's not much left except mixture.
Also try using some thick plastic or cardboard to cover the throttle mouths once its running, see what effect that has and say 1 bank...can you get the lambda on that bank to suddenly start to read high ?
It sounds like you've thoroughly exhausted the electrical angle, so there's not much left except mixture.
Also try using some thick plastic or cardboard to cover the throttle mouths once its running, see what effect that has and say 1 bank...can you get the lambda on that bank to suddenly start to read high ?
What are your symptoms? poor idle? misfire on gentle throttle? misfire at high revs?
Any one of those would indicate a throttle body / pot issue.
Are the throttle pots behaving? staying in sync over a few runs?
My money is with the AFR being wrong too.
If you cover a bank with cardboard and have air leaking in under the throttle body flanges for example, the effect may not be so obvious? If that was the case your readings on a sycrometer would also tell you fibs and balancing may be v difficult.
Are your throttle bodies worn? see my other threads for details...this is one of them...
http://www.pistonheads.co.uk/gassing/topic.asp?h=0...
Any one of those would indicate a throttle body / pot issue.
Are the throttle pots behaving? staying in sync over a few runs?
My money is with the AFR being wrong too.
If you cover a bank with cardboard and have air leaking in under the throttle body flanges for example, the effect may not be so obvious? If that was the case your readings on a sycrometer would also tell you fibs and balancing may be v difficult.
Are your throttle bodies worn? see my other threads for details...this is one of them...
http://www.pistonheads.co.uk/gassing/topic.asp?h=0...
The "cover up" trick was what finally convinced me during my woes. The effect is dramatic if you have a flange leak...cover the throttle mouths on one bank and force the leak alone to provide the air and you find that things start to resolve i.e. the lambdas start to ping-pong and the adaptives come down. Worth a try to diagnose this as its turning into a bit of a mare by the sounds of it.
Maany thanks for your comments guys. I tried covering up the throttle flanges, but it didnt seem to have any effect, so in the end I decided to just button her up as best I could and head down to my "nearest" TVR specalist, Dreadnaught. Given that this involves taking a day off work to drive 130 miles to get there, I wasn't best pleased to find that they were all booked up this week despite haveing told me otherwise. Still, I wasn't letting them try to tell me that they couldn't find a space for me to leave my car with them in order to look at it when they next can, so hopefully I'll be hearing something from them next week. A week today though I'm meant to be heading to the North of Scotland for an epic road trip, so things are indeed being cut rather fine.
I think the car probably did benefit from getting a bit of a run, and certainly on the motorway any problems aren't that noticeable, but at low speeds the engine hunts around all over the place, and basically wants to die if the revs drop below 1500. I still doubt there's anything wrong with the throttle spindle, as it all seemed tight as a preverbial tight thing, but I'm just about willing to believe anything at this point. On the up side, the drive down did remind me why I'm doing all of this- even in its poorly state the tiv still put a grin on my face.
I think the car probably did benefit from getting a bit of a run, and certainly on the motorway any problems aren't that noticeable, but at low speeds the engine hunts around all over the place, and basically wants to die if the revs drop below 1500. I still doubt there's anything wrong with the throttle spindle, as it all seemed tight as a preverbial tight thing, but I'm just about willing to believe anything at this point. On the up side, the drive down did remind me why I'm doing all of this- even in its poorly state the tiv still put a grin on my face.
Have to checked the throttles are all in sync?
Get the car warm and at idle spray carb cleaner around the flanges were they meet the head one at a time, if there is a leak you will hear it as the engine note will change. Also spray around where the throttle spindle ands are on each throttle body.
Also if you can check the output from BOTH temp sensors, one is the fans the other is engine temp for the ecu. It could be this failing, swap them over if needs be.
Get the car warm and at idle spray carb cleaner around the flanges were they meet the head one at a time, if there is a leak you will hear it as the engine note will change. Also spray around where the throttle spindle ands are on each throttle body.
Also if you can check the output from BOTH temp sensors, one is the fans the other is engine temp for the ecu. It could be this failing, swap them over if needs be.
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