High RPM missfire
Discussion
Hi all
Had my 2000 tuscan for a while now, ever since I purchased it, it's had a missfire/hesitation/rev limiter at around 5500rpm (varies although never below this) when at full throttle. Doesn't seem to happen through 1st or 2nd gear, sometimes the cut out is quite harsh like a rev limiter and the car will not pull through it unless you back off the throttle, other times it's more of a farting (best I can think of to describe it) that you can pull through eventually.
Assumed it was ignition so either coil pack or HT leads so didn't go back to the dealer on it (assuming a cheap fix). Didn't actually get around to sorting it out until a year later
This was probably foolish as after changing the coil pack and HT leads (some very nice magnacor KV85s) it's still doing it
I seem to be getting EFI fault much more persistantly than usual too. I've checked the earths and these seem ok, the crankshaft wiring is well clear of the HT leads so that leaves lambda or possibly throttle bodies?
Lambda wouldn't cause the problem at those rpms right? So that leaves throttle bodies, seems to be about the right mileage for it, going on other stories I've read. I've spoken to dreadnough though who did a 12k service on the car about 3k ago and they said it was unlikely to be throttle bodies as it would have shown on diagnotiscs.
Engine history for anyone interested:
Full Rebuild @ 19020 By Racing Green Dec 06 - No details on what was done, according to RG it was sent to TVR for rebuild so no paperwork
6k service @ 26100 By TVR Power - Before I collected the car
12k service @ 30878 By Dreadnought (2 shims required)
33k on the clock now
Before I embark on the 4 hour journey to Dreadnought, I wonder if anyone has any other ideas as I guess if it's throttle bodies I'm in for a hefty bill on top of a new clutch, radiator and another service looming
Had my 2000 tuscan for a while now, ever since I purchased it, it's had a missfire/hesitation/rev limiter at around 5500rpm (varies although never below this) when at full throttle. Doesn't seem to happen through 1st or 2nd gear, sometimes the cut out is quite harsh like a rev limiter and the car will not pull through it unless you back off the throttle, other times it's more of a farting (best I can think of to describe it) that you can pull through eventually.
Assumed it was ignition so either coil pack or HT leads so didn't go back to the dealer on it (assuming a cheap fix). Didn't actually get around to sorting it out until a year later
This was probably foolish as after changing the coil pack and HT leads (some very nice magnacor KV85s) it's still doing it I seem to be getting EFI fault much more persistantly than usual too. I've checked the earths and these seem ok, the crankshaft wiring is well clear of the HT leads so that leaves lambda or possibly throttle bodies?
Lambda wouldn't cause the problem at those rpms right? So that leaves throttle bodies, seems to be about the right mileage for it, going on other stories I've read. I've spoken to dreadnough though who did a 12k service on the car about 3k ago and they said it was unlikely to be throttle bodies as it would have shown on diagnotiscs.
Engine history for anyone interested:
Full Rebuild @ 19020 By Racing Green Dec 06 - No details on what was done, according to RG it was sent to TVR for rebuild so no paperwork
6k service @ 26100 By TVR Power - Before I collected the car
12k service @ 30878 By Dreadnought (2 shims required)
33k on the clock now
Before I embark on the 4 hour journey to Dreadnought, I wonder if anyone has any other ideas as I guess if it's throttle bodies I'm in for a hefty bill on top of a new clutch, radiator and another service looming
Edited by tezza77 on Sunday 23 May 02:00
Hi there, hope your enjoying the tuscan!
Dreadnought have a lot of experience with throttle bodies so they ought to be able to help, but, they do sound like typical worn throttle body symptoms.
Have a read of some of my posts and you can have a think if it sounds the same. BGB Autosport also went through a similar troubleshooting exercise and he changed virtually everything before the TB's.
http://www.pistonheads.com/gassing/topic.asp?h=0&a... had their throttle bodies modded with bearings?&mid=49114
http://www.pistonheads.com/gassing/topic.asp?h=0&a... i have diagnosed my poor running!&mid=49114
http://www.pistonheads.com/gassing/topic.asp?h=0&a... Bearing Throttle Bodies Fitted (and a few other bits!&mid=49114
Dreadnought have a lot of experience with throttle bodies so they ought to be able to help, but, they do sound like typical worn throttle body symptoms.
Have a read of some of my posts and you can have a think if it sounds the same. BGB Autosport also went through a similar troubleshooting exercise and he changed virtually everything before the TB's.
http://www.pistonheads.com/gassing/topic.asp?h=0&a... had their throttle bodies modded with bearings?&mid=49114
http://www.pistonheads.com/gassing/topic.asp?h=0&a... i have diagnosed my poor running!&mid=49114
http://www.pistonheads.com/gassing/topic.asp?h=0&a... Bearing Throttle Bodies Fitted (and a few other bits!&mid=49114
Thanks for your replies although I kinda wish you hadn't bothered as it's looking more like a costly bill rather than a simple fix 
Thats the joys I guess, just a shame it all comes around at the same time.
I do have a question though, how can such a small amount of play have such a big impact? I could understand it at idle but at wide open surely a bit of play can't make that much of a difference?
Thats the joys I guess, just a shame it all comes around at the same time.
I do have a question though, how can such a small amount of play have such a big impact? I could understand it at idle but at wide open surely a bit of play can't make that much of a difference?
Actually after reading those other threads it does definitely seem like TB's as I have also noticed that the engine sounds rather 'ticky'. I really should have looked at it sooner and gone back to the dealer on it, oh well... no beer for me for the considerable future then,
Dreadnought no longer offer their solution as they never had enough uptake so I guess they'll send them to somewhere like Str8 Six/TVRP. Just hope it doesn't take too long, this sunshine won't last forever
Question... how much of a ballache is it to get the TB's off (and back on of course) myself I'm not great with a spanner but I do have a mate who's pretty handy just not sure it's worth the pain. I guess the car has to go in afterwards to be setup anyway?
Dreadnought no longer offer their solution as they never had enough uptake so I guess they'll send them to somewhere like Str8 Six/TVRP. Just hope it doesn't take too long, this sunshine won't last forever
Question... how much of a ballache is it to get the TB's off (and back on of course) myself I'm not great with a spanner but I do have a mate who's pretty handy just not sure it's worth the pain. I guess the car has to go in afterwards to be setup anyway?
Edited by tezza77 on Sunday 23 May 15:04
The throttle pots are very sensitive and with even the smallest of play they overload the ecu with signals which in turn shuts it down momentarily and you see a misfire.
If you can get the bonnet and airbox off its really not much more difficult, each throttle body had four allen bolts to take out of the head. No 6 by the bulhead it the trickiest.
What i would say is if your not confident in taking them out, putting them in is risky (you may drop a bolt etc into a manifold) and setting the engine up thereafter isnt particularly easy. Also depends if you have the equipment (laptop & synchrometer) to be able to do it. If not you're probably best at str8 six. TVR Power dont offer roller bearing TB's, only rebushed (which would be fine but would only last as long as the originals). Str8 six do the full monty, removal, machining, engine setup etc, they will charge you around £600. Racing Green do reconditioned TB's with roller bearings direct from their parts shop for £300, but then you would have to do the setup yourself. I can recommend Str8 Six for service but not RG.
But, like you said, you need to get it back if the dealer still has some dealings with it, to try and ascertain if it really is the problem.
If you can get the bonnet and airbox off its really not much more difficult, each throttle body had four allen bolts to take out of the head. No 6 by the bulhead it the trickiest.
What i would say is if your not confident in taking them out, putting them in is risky (you may drop a bolt etc into a manifold) and setting the engine up thereafter isnt particularly easy. Also depends if you have the equipment (laptop & synchrometer) to be able to do it. If not you're probably best at str8 six. TVR Power dont offer roller bearing TB's, only rebushed (which would be fine but would only last as long as the originals). Str8 six do the full monty, removal, machining, engine setup etc, they will charge you around £600. Racing Green do reconditioned TB's with roller bearings direct from their parts shop for £300, but then you would have to do the setup yourself. I can recommend Str8 Six for service but not RG.
But, like you said, you need to get it back if the dealer still has some dealings with it, to try and ascertain if it really is the problem.
Robertjp said:
The throttle pots are very sensitive and with even the smallest of play they overload the ecu with signals which in turn shuts it down momentarily and you see a misfire.
If you can get the bonnet and airbox off its really not much more difficult, each throttle body had four allen bolts to take out of the head. No 6 by the bulhead it the trickiest.
What i would say is if your not confident in taking them out, putting them in is risky (you may drop a bolt etc into a manifold) and setting the engine up thereafter isnt particularly easy.
Thanks Robertjp, that info is a great help. The dealer won't be interested in it now, more than 12 months on from the sale so I'm o my own I guess. If you can get the bonnet and airbox off its really not much more difficult, each throttle body had four allen bolts to take out of the head. No 6 by the bulhead it the trickiest.
What i would say is if your not confident in taking them out, putting them in is risky (you may drop a bolt etc into a manifold) and setting the engine up thereafter isnt particularly easy.
If it's just a case of unbolting them and fitting a recon set then I think my buddy would be more than happy to give me a hand, I can see how #6 can be a bit of a b
h to do but he's pretty good with tricky things like that After having a fiddle with the shaft it seems there is no play on the middle two, a little play on the 1st two and much more play on the last two. Is just twiddling the shaft (ooh-err!) a good test or should I still take it to the dealer before coughing up another £300 for recon bodies?
It would definitely have to go into the dealer to be setup, I don't have the equipment or knowledge so I guess I need to know if it's safe to drive it to the dealer after fitting the recon bodies or am I likely to damage something?
Also, just wondered why you're not recommending RG for service... is that just because you've never used them? Not that it makes much odds to me, I live in the north east of Scotland so neither of those dealers are close enough for me to use them hency why dreadnought do my servicing.
Edited by tezza77 on Sunday 23 May 21:46
The bolting / unbolting is the easy part, setting the engine up afterwards is the difficult bit. Without equipment to get it somewhere near tuned you will struggle to get the engine to run well enough to get it anywhere for a proper tune up. Could also risk damage i guess. I really wouldn't recommend it!
Str8 Six did my rebuild and were excellent, their reputation is one of the best out there. Name and shame rules prevent me saying what i think of RG's quality of service
Although, annoyingly, their parts store is pretty good and simple to navigate.
Edited to say, that a good test is to do about 30/40 mph in 5th, light throttle accel and see if you can detect hesitation / miss. It should be silky smooth. Also, with the airbox off, if there is play you can move the shafts on the TB's and the engine running will audibly change. Another check is to zero the throttle pots and then drive for a while, then check again, if they are more than 1% or so different you have a problem (but you need a laptop for this check).
Str8 Six did my rebuild and were excellent, their reputation is one of the best out there. Name and shame rules prevent me saying what i think of RG's quality of service
Although, annoyingly, their parts store is pretty good and simple to navigate. Edited to say, that a good test is to do about 30/40 mph in 5th, light throttle accel and see if you can detect hesitation / miss. It should be silky smooth. Also, with the airbox off, if there is play you can move the shafts on the TB's and the engine running will audibly change. Another check is to zero the throttle pots and then drive for a while, then check again, if they are more than 1% or so different you have a problem (but you need a laptop for this check).
Edited by Robertjp on Monday 24th May 09:50
Well im going to fit the new rad tomorrow night so she's good to get me to Dreadnought. Whilst im doing that I'll have another look at the TBs.
I had a chat with Brian at Dreadnought today and they do have one of their bodies left but my pockets just arent deep enough for that (bodies are 1k plus vat
) , what with everything else thats needing doing. RG will ship me a recon set at the cost of only one arm and take them back no problem if it turns out not to be the problem. I'll get them ordered up and sent to dreadnought ready but I won't be able to get there for a few weeks yet.
They also suggested the 5th gear test although they reckoned on doing it at 50mph. I'm going to try that tonight and see what happens.
Thanks
I had a chat with Brian at Dreadnought today and they do have one of their bodies left but my pockets just arent deep enough for that (bodies are 1k plus vat
) , what with everything else thats needing doing. RG will ship me a recon set at the cost of only one arm and take them back no problem if it turns out not to be the problem. I'll get them ordered up and sent to dreadnought ready but I won't be able to get there for a few weeks yet. They also suggested the 5th gear test although they reckoned on doing it at 50mph. I'm going to try that tonight and see what happens.
Thanks
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