Discussion
Hi, not long acquired Cerebra Speed Six, low milage recently rebuilt engine, balanced throttles etc. Was running fine, has had gradual onset of idle suddenly increasing from 950 to 1200 for a few seconds, now getting worse, up to 1400 at times, then varies, also with intermittent misfire, as if lost a cylinder or two for up to a few minutes at a time. Only apparent with warm engine. Any clues? Is awaiting valve clearance check. Cheers
Thanks guys. I don't have the skills and there is a lack of specialists within 100miles. But it is booked in soon at a place in Glasgow, they have worked on Speed sixes, and will no doubt have the relevant software. The garage down the road thought it might be an air leak, not having looked yet, and asked whether it was an OBE type connection to the ECU?
DCerebrate said:
Thanks guys. I don't have the skills and there is a lack of specialists within 100miles. But it is booked in soon at a place in Glasgow, they have worked on Speed sixes, and will no doubt have the relevant software. The garage down the road thought it might be an air leak, not having looked yet, and asked whether it was an OBE type connection to the ECU?
Not OBE Type............Depending on the age of your Cerb, the MBE will either have a port on the ECU or a flying 3-pin under the dash; see here:http://www.pistonheads.com/gassing/topic.asp?h=0&f=6&t=1273904&i=500&mid=23805&nmt=ECU+Diagnostic+Software+Re%2DWriteIt's a lot to read, but may give you some info on running your own diagnostics?
HTH's
T
Rebuild done with previous owner and Str8six for all their genius are not good at paper trails. I do have evidence that engine was sent by a TVR specialist to Str8six in 2012 and returned, refitted. If crank sensor, would that mean I should not drive the car? Another suggestion was air intake leak? No problem when cold.
Rebuild done with previous owner and Str8six for all their genius are not good at paper trails. I do have evidence that engine was sent by a TVR specialist to Str8six in 2012 and returned, refitted. If crank sensor, would that mean I should not drive the car? Another suggestion was air intake leak? No problem when cold.
DCerebrate said:
Rebuild done with previous owner and Str8six for all their genius are not good at paper trails. I do have evidence that engine was sent by a TVR specialist to Str8six in 2012 and returned, refitted. If crank sensor, would that mean I should not drive the car? Another suggestion was air intake leak? No problem when cold.
Agree, records on individual cars are a bit haphazard at STR8Six.Having said that, is the previous owner contactable? If so ask him/her for the relevant paperwork. I find it odd that for a big ticket item like an engine rebuild, the previous owner hasn't passed on either the bill from the "TVR Specialist", or the job sheet/invoice from the engine builder?
I would still suggest that your 1st move should be to get it hooked up to the diagnostics. A faulty crank sensor will show as a fault (funnily enough!). Air leaks are possible around the throttle bodies. I believe most folks test for this by squirting "EASY-START" to the throttle body/cyl. head joint and seeing/listening for an increase in rpm.
Nick
For an engine to increase in speed, it must get more air, so no amount of faulty sensors could cause it to speed up on their own.
I think an air leak is the most probable cause - mine was massively improved by removing and re-sealing the throttle bodies. It's a fairly under-promoted fix that costs next to nothing in parts (if using RTV) and doesn't take that long if you're handy with an allen key.
...but getting the diagnostics working whether via a laptop or the RS-AJP app makes diagnosis sooo much simpler. If the lambdas are reading lean but the exhaust smells rich, bingo splingo, vac leak. Mine was doing it when cold then calming down as it warmed up.
As above, once you've done work like this, you must re-set the throttle pots and adaptives in the ECU.
I think an air leak is the most probable cause - mine was massively improved by removing and re-sealing the throttle bodies. It's a fairly under-promoted fix that costs next to nothing in parts (if using RTV) and doesn't take that long if you're handy with an allen key.
...but getting the diagnostics working whether via a laptop or the RS-AJP app makes diagnosis sooo much simpler. If the lambdas are reading lean but the exhaust smells rich, bingo splingo, vac leak. Mine was doing it when cold then calming down as it warmed up.
As above, once you've done work like this, you must re-set the throttle pots and adaptives in the ECU.
Air leaks from under the bodies or linkages normally don't come suddenly.
The idle increase only occures when hot, so air leaks are only there when hot ? I don't think so.
Pull the plug from one of the pots and you'll see that the engine is running nuts as if one or two cylinders are without ignition.
The idle increase only occures when hot, so air leaks are only there when hot ? I don't think so.
Pull the plug from one of the pots and you'll see that the engine is running nuts as if one or two cylinders are without ignition.
Gasketed joins, eg exhausts typically get better as they warm and things expand. The throttles aren't gasketed so there's no reason why differential expansion couldn't cause a worse leak.
Doesn't the ECU simply take the signal from the other TPS if one drops? Maybe if it acts badly at that point it's because the two "banks" are pretty different to start with...
Doesn't the ECU simply take the signal from the other TPS if one drops? Maybe if it acts badly at that point it's because the two "banks" are pretty different to start with...
Yes, you can read everywhere that the ECU takes the readings from the other pot, but after synchronizing my throttles that are ball beared and fitted with powers gaskets, so both banks were excellent in sync, i testwise pulled one pot and what happened ? The engine was running nuts.
I had air leaking under the bodies and leaky linkages, too. But when cold the engine was running much smoother than when it was hot. Just saying...
I had air leaking under the bodies and leaky linkages, too. But when cold the engine was running much smoother than when it was hot. Just saying...
If you want to have the throttle bodies refurbished contact Andy, he provides an excellent job. He sells gaskets as well. See here
http://www.pistonheads.com/classifieds/parts-and-p...
http://www.ebay.co.uk/itm/TVR-SPEED-6-SIX-Throttle...
or here
http://www.ebay.co.uk/itm/Tvr-Speed-Six-Throttle-B...
Check this thread here too:
http://www.pistonheads.com/gassing/topic.asp?h=0&a...
If you have done the first 2 modifications your problem should be solved. If not, you have done something to keep idle running properly aligned for long time. The lambda mod is a no brainer too.
Peter
http://www.pistonheads.com/classifieds/parts-and-p...
http://www.ebay.co.uk/itm/TVR-SPEED-6-SIX-Throttle...
or here
http://www.ebay.co.uk/itm/Tvr-Speed-Six-Throttle-B...
Check this thread here too:
http://www.pistonheads.com/gassing/topic.asp?h=0&a...
If you have done the first 2 modifications your problem should be solved. If not, you have done something to keep idle running properly aligned for long time. The lambda mod is a no brainer too.
Peter
Edited by crypto on Sunday 3rd May 14:18
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