Automatic transmission hesitation

This forum is specifically for engine and gearbox posts, please try to keep on topic in any thread to make things easy to find

Moderator: Board Moderators

fairline38
Junior Poster
Posts: 43
Joined: Sat Aug 19, 2017 16:46
Model: Excel SA
Colour: Black
Year: 1987
Location: London Finchley
Contact:

Re: Automatic transmission hesitation

Post by fairline38 »

So...it's been almost three years since I visited this topic.

Ultimately, the hesitation problem (fade out at start-off - low speed acceleration) returned.

In late 2019, I took the car down to a carburettor specialist near Winchester on the recommendation of another owner.

These guys definitely know what they are doing.

They first tested the SA on their rolling road and she was putting out just under 125hp at the rear wheels.

After about an hour of intense testing, they changed the jets, retuned the carbs, and retested her. The changes raised the hp to 166! I wouldn't have believe it unless I had stood there and watched the process.

It was a bit disappointing that they would not road test the car themselves. Also, I paid over £ 300 for less than two hours time, which I felt was excessive, although they did have all the equipment. For that money I thought they were going to remove and rebuild the carbs. (In all fairness, their website did state exactly what the process was and that they do not test drive owner's vehicles).

One observation is that upon warm-up, the volt meter flutters with the rough idle. This has led me to believe that this may be an electrical problem.

My next step is to have a local specialist retune the carbs.

richardw
Moderator
Posts: 2224
Joined: Wed Feb 06, 2013 15:06
Model: Elite S2.2 Automatic
Colour: Essex Blue
Year: 1981
Location: Worcestershire

Re: Automatic transmission hesitation

Post by richardw »

I don’t think that £300 is bad at all for what they did, which is fix your problem and give you a lot more power. Great result!

Richard
Image

User avatar
Lotus-e-Clan
Senior Poster
Posts: 4454
Joined: Thu Nov 30, 2006 13:25
Model: Excel SE - EWP/Waterless!
Colour: Not Blue or Green
Year: 1989
Location: Swaledale

Re: Automatic transmission hesitation

Post by Lotus-e-Clan »

fairline38 wrote:
Sun Nov 01, 2020 11:39
So...it's been almost three years since I visited this topic.

Ultimately, the hesitation problem (fade out at start-off - low speed acceleration) returned.

In late 2019, I took the car down to a carburettor specialist near Winchester on the recommendation of another owner.

These guys definitely know what they are doing.

They first tested the SA on their rolling road and she was putting out just under 125hp at the rear wheels.

After about an hour of intense testing, they changed the jets, retuned the carbs, and retested her. The changes raised the hp to 166! I wouldn't have believe it unless I had stood there and watched the process.

It was a bit disappointing that they would not road test the car themselves. Also, I paid over £ 300 for less than two hours time, which I felt was excessive, although they did have all the equipment. For that money I thought they were going to remove and rebuild the carbs. (In all fairness, their website did state exactly what the process was and that they do not test drive owner's vehicles).

One observation is that upon warm-up, the volt meter flutters with the rough idle. This has led me to believe that this may be an electrical problem.

My next step is to have a local specialist retune the carbs.
They could have made 3 or 4 adjustments to increase the max power at the wheels from 125 to 166 bhp - unrelated to changing jets.
    • 1) rebalanced the throttle plates physically
      2) adjusted the throttle cable to fully open the throttles
      3) reset the float levels
      4) reset the maximum mechanical ignition advance to spec.
It's VERY unlikely that the factory spec jets (Mains, Airs, emulsion tubes, idle jets or the Lotus-specific power jet) were wrong and causing reduced maximum power.

You now have a rough idle, which has many causes and cures, and doesn't exclude the possibility of inappropriate jet changes or other adjustments made during the 2019 session.
Maximising power is the easiest and most profitable adjustment to make on a rolling road. Optimising driveabilty is much harder.
So jury's out on whether it was £300 well spent. :?
Peter K

fairline38
Junior Poster
Posts: 43
Joined: Sat Aug 19, 2017 16:46
Model: Excel SA
Colour: Black
Year: 1987
Location: London Finchley
Contact:

Re: Automatic transmission hesitation

Post by fairline38 »

Here is an update on the SA auto box hesitation from start-off...turns out that the idle balance lever had been jimmied by someone in the past. I was able to source a new carb balance lever for the Dellorto 45 carb with both balance barrels attached. It is part number 11129 - Lotus Turbo Balance Lever from Eurocarb. Speak to Travin. He was incredibly helpful. You can fine turn the balance lever to remove the engine low rpm hesitation. The engine idle is perfectly smooth now and acceleration and kickdown is perfect.

User avatar
Hawaiis0
Senior Poster
Posts: 4130
Joined: Sun Jun 30, 2013 18:39
Model: Excel SA (No 3); Elite 504
Colour: BRG; Dirty White
Year: 1986
Location: West Oxfordshire

Re: Automatic transmission hesitation

Post by Hawaiis0 »

Very interesting report.

How long have you been running 'fixed', as after a earlier attempt the symptom came back?

My similar hesitation would come and go with out warning. Cant try your fix as now the engine and Gearbox are up for refurb.

Stu
Nothing is fool proof. Fools are clever!

Online
Pete Boole
Senior Poster
Posts: 3711
Joined: Tue Apr 04, 2006 21:28
Model: Elite
Colour: Monaco White
Year: 1974
Location: Nottingham

Re: Automatic transmission hesitation

Post by Pete Boole »

Yes - a very interesting thread. I'm in the process of fitting a ZF into my Elite, but with fuel injection etc. It will be interesting to see how it runs!

Pete

Zaphod
Senior Poster
Posts: 242
Joined: Mon Aug 23, 2021 21:38
Model: Excel SE
Colour: Blue
Year: 1990
Location: Uffington

Re: Automatic transmission hesitation

Post by Zaphod »

Am I right in thinking the autobox used in the SA is a ZF HP422? If so did lotus use the fix that Jaguar and later Land Rover did to stop premature wear in the 1st gear clutch pack? This was a fault that plagued BMWs and Volvos that used this gearbox and the earlier 4 speed auto range rovers. There is a condition that occours when the gearbox has a slight wear on one of the seals which means there is always some drag on the first gear clutch pack. Initially it manifests as a reluctance to change gear till warm, sometimes the gearbox will stick in first when driving off then when warmed up normall operation is resumed. In later stages it will either loose all forward gears or reverse. The fix was simple, a hole was drilled to relive the unwanted pressure, this was applied to all jaguars using the gearbox which would normally outlast the car, the same can’t be said of the BMWs that used it. The problem was so bad California exempted cars using it from the high RPM part of their smog tests as cars had failed at the testing stations!
Of all the things I have lost I think I miss my mind the most...

1952 MG TD
1957 MGA 1500
1959 Austin Healey Sprite
1975 MG Midget 1500
1990 Lotus Excel

User avatar
Hawaiis0
Senior Poster
Posts: 4130
Joined: Sun Jun 30, 2013 18:39
Model: Excel SA (No 3); Elite 504
Colour: BRG; Dirty White
Year: 1986
Location: West Oxfordshire

Re: Automatic transmission hesitation

Post by Hawaiis0 »

Zaphod wrote:
Mon Feb 19, 2024 19:44
Am I right in thinking the autobox used in the SA is a ZF HP422?
Yes the 4HP22 is the box used. I'm not sure if that fix is built in. I will enquire with Ashcroft's when i send mine in for overhaul.
Nothing is fool proof. Fools are clever!

Online
Pete Boole
Senior Poster
Posts: 3711
Joined: Tue Apr 04, 2006 21:28
Model: Elite
Colour: Monaco White
Year: 1974
Location: Nottingham

Re: Automatic transmission hesitation

Post by Pete Boole »

Hawaiis0 wrote:
Mon Feb 19, 2024 21:38
I'm not sure if that fix is built in. I will enquire with Ashcroft's when i send mine in for overhaul.
Thanks Stu - let us know what comments they make about that.

Pete

Post Reply