shunting

[storm grey]

just come back from tag 11 and the shunting at low speeds is starting to do my head in anything under 45 and it shunts after that it drives fine also noticed it seems to be running rich on startup .wots my best option ? thanks

[carsy]

Most are rich on start up. Some people have sorted the shunting by adding a plenum spacer. Best way is Megasquirt ecu or similar. Some people have resorted to a carb to sort it. There are many threads on shunting if you go onto the search.

[storm grey]

already put a thermal spacer on didnt make a difference what sort of money is a mega squirt and is it a diy job ?

[CHGRIFF]

The thermal gasket was developed to reduce intake temperature by limiting the heat transfer from the intake manifold to the trumpet base, it will have no affect on shunting issues.
Customers who bought the Plenum spacer and or bell mouth package to improve engine breathing have given feedback saying their shunting issues have been resolved.
Contact SC Power to discuss further if interested to resolve this issue with a plenum spacer and or bell mouth system.

[900T-R]

Before resorting to bolting stuff to your engine, first make sure the basics are right. Do you have any air leaks? Is the stepper motor functioning correctly (to be sure, best thing is to swap with a 'known good' example as not all stepper motor faults will show up on the ECU diagnostics as fault codes)? Is the throttle potentiometer working as it should and base idle set correctly?

[M@H]

900T-R said:

Before resorting to bolting stuff to your engine, first make sure the basics are right. Do you have any air leaks? Is the stepper motor functioning correctly (to be sure, best thing is to swap with a 'known good' example as not all stepper motor faults will show up on the ECU diagnostics as fault codes)? Is the throttle potentiometer working as it should and base idle set correctly?

thank goodness for a voice of reason.

"I have a problem with the running of my car" = "rush out and buy different aftermarket bits for the engine" - bonkers

[blitzracing]

As the man says . As for running richer, it does help, but the ECU wont allow it in catalys mode. Ive tried to frig it to force the ECU to at least try and run on the rich side of the catalyst cycle, but all it does is suddenly let go as you hit the limits so it either runs at lambda 1 or far too rich, theres no in between.

[TVR Beaver]

TVR Beaver said:

CHGRIFF said:

The thermal gasket was developed to reduce intake temperature by limiting the heat transfer from the intake manifold to the trumpet base, it will have no affect on shunting issues.
Customers who bought the Plenum spacer and or bell mouth package to improve engine breathing have given feedback saying their shunting issues have been resolved.
Contact SC Power to discuss further if interested to resolve this issue with a plenum spacer and or bell mouth system.

I know these things vary a lot.. But when I and Chris52 fitted the insulating gasket to our cars.. It solved a lot of the shunting issues... not sure on the spacer... (Plenum one) as I made a 10mm one and it's always been there....(But ensure the basics are right first)
I also moved the advance / retard position so it started at 1600 rpm.. that helped... Running richer I would think will help the issue... does it run rich when warm also?
.


Yes.. the smalles air leak will cause this for sure... Even plenum to base and base to manifold.. check the lot..

Edited by TVR Beaver on Tuesday 7th June 13:21

[taylormj4]

I have had moderate shunting with my 450 for 8 years and as it's a daily driver it could get quite annoying; shifting to neutral or dipping the clutch all the time. Have tried numerous things and asked fro it to be looked at during servicing to no avail. However recently, I disconnected the stepper motor as others have done and it is a million times better. I can now quietly follow along in traffic with next to no shunting, even with revs below 1000rpm - different car.
Try it. I have just run a thread on this topic and would provide you a link to it if I knew how.

[M@H]

The problem with disconnecting your stepper (or blanking it off) is that you are potentially covering up for a fault elsewhere - it does indeed seem to be a "magic cure" for many TVR owners but the bottom line is that it isn't actually solving the root cause. TBH though, many people are very happy just to have the problem "go away" and not have to spend the cash on root cause analysis so its just a case of individual choice

Cheers,
Matt.

[lestershaw]

i am not sure if i have the dreaded "shunting" as i only get the symptoms at higher revs 3000 and above. it does not happen all the time and when it does its usually only cruising in 5th, but recently when its happened its got progressively worse and then in all the gears. it seems to me it only starts when the car gets warmed up, and/or if i have been pushing it beforehand, any ideas?
the symptoms are, hesitancy in going on, the revs drop suddenly and shoot back up. usually if i give it some welly it drives through the problem until i back off and then it hesitates again.

[M@H]

Could be a host of things but the described "shunting" is normally much lwer down the revs (circa 1500) - I would probably start with checking the coil and ht lead connections and have a peek under the distributor cap.

Cheers,
Matt.

[lestershaw]

Hi Matt, i just got the car back from a service, and also trying to find a cure to my car running lean.They found an air leak at the plenum, and a 4.0 litre ecu and chip ! luckily i had given them a spare 5.0 litre ecu and chip just in case and when they swapped the ecu and chip over and cured the air leak, i gained another 25 bhp or so. But i have now got this other problem. would they have checked during the distributor etc during the service?
Lester

[M@H]

A normal service would not include inspeciton of the rotor arm but if someone was investigating poor running they may well have had a look. I am mystified why you had the wrong ECU, TVR usually wrote in big letter in marker pen on them what they were so no room for confusion.

I would always start with the simple things like plugs, leads and coil if there is an issue like this It could be that despite their longevity that your coil is breaking down for instance..

Cheers,
Matt.

[tvrman]

lestershaw said:

i am not sure if i have the dreaded "shunting" as i only get the symptoms at higher revs 3000 and above. it does not happen all the time and when it does its usually only cruising in 5th, but recently when its happened its got progressively worse and then in all the gears. it seems to me it only starts when the car gets warmed up, and/or if i have been pushing it beforehand, any ideas?
the symptoms are, hesitancy in going on, the revs drop suddenly and shoot back up. usually if i give it some welly it drives through the problem until i back off and then it hesitates again.

I suggest check the rotor arm and check it fits firm onto the dizzy. This *may* have solved my issue. While you are at it, clean up the rotor arm and check the contact in the dizzy cap touches the rotor arm (sometimes not pushing rotor arm all the way home, by 1mm may help).

Ian

[lestershaw]

Thanks Ian and matt for your input. I will get the rotor arm looked at and let you know the results