Chim 450 Low Rev Misfire

[DamnWiseguy]

Hi all,

Dead chuffed after picking up my 1st TVR on Saturday, a '98 R 450. It's everything I imagined!!

However I have a couple of questions i'm hoping you can help me with. Will post them separately so don't worry!

1)My car misfires under 2000 rpm leading to kangarooing around town, and fuel popping in the manifold and a lot of vibration at idle. The problem disappears with a bit of throttle. Having searched the archives I see a lot of people have the same problem however there are few posts with any results! Before I start replacing expensive ignition parts does anyone have any ideas? The car has just been serviced although has been standing at the dealers where it was for sale for a few months.

I know I should clean the stepper motor maybe, where is it? The plug leads don't look new although it pulls like a train over 2000rpm so I'm not sure it is them.

Would appreciate any help.

[2 sMoKiN bArReLs]

I just ignore this trait. Also some days it'll idle at 2,000 rpm, and a bit later not at all.

In my experience all fixes seem to be fairly short lived.

Good luck...you'll get used to sitting in traffic with the ball of your foot on the brake (no hand brake!) whilst using the edge of your foot on the throttle to keep the revs up!

Kinda fun really.

[DamnWiseguy]

Thanks 2, obviously I didn't expect it to drive like a micra and I can live with it but have a warranty so would like to try to get any potential issues sorted. Actually thought it might be entirely normal and that it was just off-cam at these revs!

[2 sMoKiN bArReLs]

DamnWiseguy said:

Thanks 2, obviously I didn't expect it to drive like a micra and I can live with it but have a warranty so would like to try to get any potential issues sorted. Actually thought it might be entirely normal and that it was just off-cam at these revs!

If under warranty, take it back & ask 'em to look at it anyway.

[Red V8]

Suggest you get hold of a bible... i.e. published by Steve Heath, available from the TVR Car Club

[DamnWiseguy]

Red V8 said:

Suggest you get hold of a bible... i.e. published by Steve Heath, available from the TVR Car Club

Bible on order already!

[tops2]

Just got mine a week last friday, it's a 4.0hc.
It has the same problem , i have the bible and looked at the normal problem areas and everything is o.k.
The guys at Silverstone preformance said it could be that the ECU needs to relearn as it was also stood around for a 2 months with a flat battery.?
I have tried also unplugging the ECU to make it go in default mode but its still there.
I put optimax in it ,and it is a little better than on BP ultimate.

[greenv8s]

You'll find that trickling along in gear with no throttle, the engine will often start shunting below 1500-2000 revs. But it shouldn't misfire, and in neutral it should idle steadily with no misfiring or popping/banging. That suggests the fuelling or timing aren't set up right, so get your favorite TVR dealer/specialist to have a look at it. If this sort of problem is left then you can start damaging other components.

[Nick_Chim]

I'd try the stepper motor as a simple fix; it seems to reduce (but not elimintate) this trait in mine - although it still acts similarly in negative temperatures...

Step-by-stepper guide
www.car1.clara.co.uk/tvr/stepper.htm

I use spray carb cleaner to clean it and the 'ole.

CAUTION: Don't overtighten when re-fitting - but then don't leave it loose either!

[tops2]

Green V8s , i just looked at your pic's that looks angry. I bet its interesting in these road conditions!!
Yeh mine does not missfire , very just shunty at constant throttle 1500rpm , say in a 30 mph limit in 4th. when trying to keep the volume down.

[greenv8s]

tops2 said:

Green V8s , i just looked at your pic's that looks angry. I bet its interesting in these road conditions!!

Yes, with nearly double the original torque it does get 'a bit lively' this time of year.

[DamnWiseguy]

Nick_Chim said:

I'd try the stepper motor as a simple fix; it seems to reduce (but not elimintate) this trait in mine - although it still acts similarly in negative temperatures... Step-by-stepper guide www.car1.clara.co.uk/tvr/stepper.htm I use spray carb cleaner to clean it and the 'ole. CAUTION: Don't overtighten when re-fitting - but then don't leave it loose either!

Will clean the stepper tonight, tightened up all the connections to the coil last night and checked the resistance of the HT leads and all seemed to be well there. Coil looks a bit ancient though, kind of rusty and peeling so maybe I should change that? Still reluctant to shell out £55 if there is no benefit.

Thanks for the responses.

[mbrannon]

Remapped ECU from Dom at TVR Power :-) does the job and makes it so much more fun to drive

[ms89028]

Other thing to maybe get changed is the water temp sensor that feeds the ECU - these corrdoe, it's cheap to change and fairly easy and was the cause of lumpiness on my Chimaera 400 - it's a fairly well know problem as far as I can see.

But as others have said below about 2000 revs in traffic it can be a bit lumpy anyway and I find I tend to drive in a lower gear than "Normal" to compensate and keep the revs at or above 2K.

[andy-w]

I have a 4ltr HC and it very rarely likes to go along in 4th gear doing 30...it starts shunting and doesnt feel good...knock it down a gear and it is fine!!!

Also sometimes idles at 2000 revs and then later no idle...the more you drive it the more you get a feel for the car...give it a good blast if it has been stood around for a few months...!!!

[DamnWiseguy]

Thanks everybody, cleaned the connectors on the water temp sender and the soot from the stepper motor. Used a cotton wool bud to get all the black stuff out of the hole in the intake.

Car is now running at least 50% better. I guess it is always a combination of things, will probably change the coil and leads as well at a later date.

[jonywishbone]

I would strongly recommend that you run the car in a dark environment i.e. in a garage at night. Wait a few minutes until your eyes get adjusted and then check over the engine to make sure there's no shorting anywhere (visible by sparks) you may have to rev the engine a bit so an assistant may be useful. Careful no loose clothes in the dark. I found no1&2 cylinder leads were touching the Aluminium swirl tank at the distributor and shorting out at low revs. At higher revs the shorting doesn't seem to matter for some reason I couldn't work out. I insulated the tank and that solved it.

[rev-erend]

This happened to my 450 SEAC after I changed the distributor cap - this has obviously altered the timing by a few degrees.

The answer is just to re-time the engine.

Mine is jerky at 1k~2K then after that it flies.

Yours might be the same problem.

[DamnWiseguy]

Noticed this morning that my Ice warning light now works, cleaning the temperature sender connectors must have worked. Car is noticably better now and no popping from the manifold anymore. Think it was running rich as it thought the engine was always cold.

Still not perfect though, will check for shorts from the HT leads. How do you do this in a dark garage without gassing yourself!?

Maybe it will be worth a rolling road session.

[jonywishbone]

Your ice warning light is on a completely different circuit to the temperature sender so I think this is a pure coincidence, if you leave the doors of the garage open then you shouldn't suffocate for several minutes. Have you tried checking the resistance of the above sender its something like 2000ohms at cold and 280ohms at 83c which is engine running temperature. A jug of boiling water (to submerge the tip)a digital thermometer from her indoors and a couple of crocodile clips is althats required then record the resistance as the temperature cools if it stays high when hot then its faulty.