Slight hesitation under 2000 RPM
Discussion
Hi,
Out for a bit of a drive in the TVR yesterday. I noticed that there’s still a kind of clicking interference through the stereo, might be something to do with how the FM antenna amplifier is wired perhaps. On a more annoying note, it’s got a slight misfire when driving at under 2000 RPM. It’s mostly fine and probably not noticeable to most people, but I notice it and it bugs me! I’ll be driving at a constant speed and the car is always very slightly missing and you can feel for a split second a tiny hesitation. So instead of just moving nice and smoothly when cruising at a constant RPM, it jolts just a tiny bit on and off. It feels like it’s at random, but there might be a pattern. It’s barely noticeable, but once you notice it, it’s annoying! I don’t think it’s the shunting people speak of. I did ask a specialist to look at it, he said he had sorted it, but it’s no different.
Get over 2000 RPM and it’s fine. It will cruise at any RPM really smoothly and it pulls really well too. There is however, a very slight hesitation when accelerating hard, once it gets to 3000 RPM. It pulls hard up to 3000 RPM, then has a slight hesitation, and then pulls hard again.
Any ideas what this might be?
I will check Rover Gauge tonight to see if it gives me any useful info. Current spec is:
1997 400 Serp engine
MC1 cam fitted a year ago
ACT carbon superflare trumpets and thermal gasket
ACT induction kit
New Bosch HT leads, new plugs and extenders
It has run really well since this was all fitted, no shunting or misfires. What should I look to change next? The coolant temperature sender is about 18 months old, so I should think that it’s still ok. I’ve got a spare coil and ignition amplifier I could try, but I doubt it’s to blame. Could the lambdas have anything to do with it? I will check to see what they’re doing tonight.
Thanks,
Dan
Out for a bit of a drive in the TVR yesterday. I noticed that there’s still a kind of clicking interference through the stereo, might be something to do with how the FM antenna amplifier is wired perhaps. On a more annoying note, it’s got a slight misfire when driving at under 2000 RPM. It’s mostly fine and probably not noticeable to most people, but I notice it and it bugs me! I’ll be driving at a constant speed and the car is always very slightly missing and you can feel for a split second a tiny hesitation. So instead of just moving nice and smoothly when cruising at a constant RPM, it jolts just a tiny bit on and off. It feels like it’s at random, but there might be a pattern. It’s barely noticeable, but once you notice it, it’s annoying! I don’t think it’s the shunting people speak of. I did ask a specialist to look at it, he said he had sorted it, but it’s no different.
Get over 2000 RPM and it’s fine. It will cruise at any RPM really smoothly and it pulls really well too. There is however, a very slight hesitation when accelerating hard, once it gets to 3000 RPM. It pulls hard up to 3000 RPM, then has a slight hesitation, and then pulls hard again.
Any ideas what this might be?
I will check Rover Gauge tonight to see if it gives me any useful info. Current spec is:
1997 400 Serp engine
MC1 cam fitted a year ago
ACT carbon superflare trumpets and thermal gasket
ACT induction kit
New Bosch HT leads, new plugs and extenders
It has run really well since this was all fitted, no shunting or misfires. What should I look to change next? The coolant temperature sender is about 18 months old, so I should think that it’s still ok. I’ve got a spare coil and ignition amplifier I could try, but I doubt it’s to blame. Could the lambdas have anything to do with it? I will check to see what they’re doing tonight.
Thanks,
Dan
Try clamping off the rubber hose that goes from the plenum to the carbon canister, its the front one of two you'll find on the right side of the plenum.
Go for a drive with it clamped off and see if things improve, be careful as if you clamp the wrong hose you'll disable your brake servo and stopping will become a challenge.
Go for a drive with it clamped off and see if things improve, be careful as if you clamp the wrong hose you'll disable your brake servo and stopping will become a challenge.
Looks like new AFM are £215 for a so say genuine one. Don't want a cheap eBay one. I don't want to spend that much money if I'm not sure if it's the cause of the problem. Anyone got one spare I could borrow?
I think it's possible it's a misfire, would that tally up with -100% negative fuel trim? It felt like it had a misfire when I drove it last night. I guess the next thing to check is rotor and distributor cap.
I think it's possible it's a misfire, would that tally up with -100% negative fuel trim? It felt like it had a misfire when I drove it last night. I guess the next thing to check is rotor and distributor cap.
Well here is a video I made last night. Apologies for the terrible quality, my phone won't upload in HD over 3G and I've got no wifi here at the moment. I’ll upload an HD copy this evening when I have wifi.
But you can see that I'm driving at a constant speed and constant revs. You can see how much the car is jerking from the movement in the camera! The AFM reading is constant, no jumping around, but the lambda readings are jumping about with each misfire. One side positive, the other side negative. I guess that’s it compensating for one cylinder not firing. Could some work out which side it’s likely to be on from the data?
TPS, stepper motor and AFM all seem to be reading what they should be.
https://www.youtube.com/watch?v=As6_jRhx3gg
But you can see that I'm driving at a constant speed and constant revs. You can see how much the car is jerking from the movement in the camera! The AFM reading is constant, no jumping around, but the lambda readings are jumping about with each misfire. One side positive, the other side negative. I guess that’s it compensating for one cylinder not firing. Could some work out which side it’s likely to be on from the data?
TPS, stepper motor and AFM all seem to be reading what they should be.
https://www.youtube.com/watch?v=As6_jRhx3gg
FlipFlopGriff said:
You've changed the leads, plugs and extenders. Put the old ones back to see if it runs OK and then change one at a time to isolate the issue before trying something else.
FFG
I changed all of these quite some time ago, I think the end of last year, so they're not brand new. But I still have them, so I will swap them out to see if it changes everything. FFG
I had planned to test leads and extenders with my multimeter last night, but for some reason it's stopped working.
I'm going to stick a new battery in there tonight to see if it sorts it! Hopefully I'll find a dead extender or something. 
Not had much time to really look at the TVR, so I'm probably going to have to take it to TVR 101 for them to look at it. I have just changed the plugs during my lunch break and all of the old plugs were really really black. They aren’t very old, probably only done 1000 miles on them. It runs better on the new plugs, but it’s still jerky to drive, just not as much. I am thinking that if all of the plugs are black, then it’s a problem common to all cylinders. No plug was any different to any of the others. AFM?
I've got a new distributor cap and a rotor arm coming tomorrow.
However, today I changed the plugs. Felt ok, better but still missing. This evening I thought I'd try it without extenders fitted and it's perfect! Ok, not perfect, but nearly. The misfiring and hesitation seems to have gone, it's much smoother to drive now. Really pleased with how it drives, no shunting.
Having looked at the extenders, the black plastic on each extender is split. They're the same brand as my old ones, but they look different. Every one has split!
So at the moment I have two extenders on the rear plugs, and none on the other 6. I may buy some heatproof socks for them and do without the extenders for good. Or I may put my old (good) extenders on.
However, today I changed the plugs. Felt ok, better but still missing. This evening I thought I'd try it without extenders fitted and it's perfect! Ok, not perfect, but nearly. The misfiring and hesitation seems to have gone, it's much smoother to drive now. Really pleased with how it drives, no shunting.
Having looked at the extenders, the black plastic on each extender is split. They're the same brand as my old ones, but they look different. Every one has split!
So at the moment I have two extenders on the rear plugs, and none on the other 6. I may buy some heatproof socks for them and do without the extenders for good. Or I may put my old (good) extenders on.
QBee said:
I have recently had an issue with brand new plug extenders (March time) - 3 faulty ones out of 9. 2 worked, but didn't stay clipped onto the plug, one was electrically dead. All from a top source and genuine parts. Bad batch.
Well done for trying them without extenders. I don't want to name and shame an innocent supplier, so will email you where mine came from.ChimpOnGas said:
That's the plan. Oh, and those resistive plugs have completely cured my radio reception issue. Now I can get all the channels that my others car can get and with perfect reception!
I'm looking into the heatshield boots for the leads.
On that note, has anyone made up a stainless steel heatshield which could mount to the manifold to shield direct heat from the HT leads. feasible? Certainly should be for the driver's side, maybe not the passenger side.
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