Low End Misfire.....

[matt-man]

Hey all,

Well, after lots and lots of trouble free miles, took her out last night and ive just started getting a misfire between 1000-2000 rpm. Strange as over this its fine, and if you give it hell she pulls fine all through the rev range..

Im thinking hopefully another service, plug clean and leads might do the job...

any ideas? PS, its idling spot on..

[adam quantrill]

Check the throttle pot?

[pwd95]

Aye, had exact same thing. Changed the TP, cured it.

[matt-man]

Throttle pot? Sorry to sound silly, but im more of a nut and bolt man than engine fixing!

Ignorance is sometimes bliss!!!

[gsx600]

The bit attached to the plenum by the butterfly with 3 wires going to a connector plug on to the loom

Measure the resistance from the plug after disconecting it move the throttle and you should see resistance changing, also need to set up for the base but can't remember the seting in millivolts

I'll be doing all this over the weekend to see why mine not running , but I suspect more of the fuel regulator as when I unplugged a hose seconds after running the engine it did not spray everywhere

I'm sure someone will be along with the correct procedure and settings, as mine is at home somewhere

[TVRleigh(BBWR)]

Check out
http://www.rangie.com/files/167_387.jpg


Also a quote from Rev. in previous thread.
http://www.pistonheads.com/gassing/topic.asp?h=0&a...

rev-erend said:

Fom what I understand ..

You set the start position to around 0.3 ~ 0.35 volts as that is what the ecu is expection as a base figure.

0.8 volts is too high.

[pwd95]

Ere iw go. Starts at .32v up to 4ish v

[TVRleigh(BBWR)]

Also there in info on the RPI site.

http://www.v8engines.com/carbs-2.htm#setting-up

[legit]

I have exactly the same thing. Just changed all the leads, plugs and dis cap. Is the throttle pot is to replace? Whats it from?

[adam quantrill]

There are two types, the small one (pic above) and the large one (about 2x dia and 2x height too).

I don't think they are interchangeable. Range rover parts dept for replacements.

I have refurbished the large ones and can still do so for £10 a pop plus SAE.

[matt-man]

Lovely stuff guys! Ill give that a go later me thinks! Ill keep you posted with the result!

[gsx600]

pwd95 said:

Ere iw go. Starts at .32v up to 4ish v

Oi where is you distrubuter vacumm going from or do you have after market ecu ?

[TVRleigh(BBWR)]

Well spoted.
Also its a flapper, as it has the stright non tapped breather.

[pwd95]

Yep flapper, can't give you the history of the vacumm, thats how it came. Runs fine. It has an adjustable ecu which I was going to look at fiddling with but after speaking with one of the engine builders who was at JE when my engine was built, he said the engine would have been set up on the dyno and the ecu set for that particular engine. Add to that the fact that it gave 315 ft/lbs of tourque on the rollers at BBWF without any fuss, smoke or pinking tells me that it must be in the correct position.

[rev-erend]

gsx600 said:

The bit attached to the plenum by the butterfly with 3 wires going to a connector plug on to the loom

Measure the resistance from the plug after disconecting it move the throttle and you should see resistance changing, also need to set up for the base but can't remember the seting in millivolts

I'll be doing all this over the weekend to see why mine not running , but I suspect more of the fuel regulator as when I unplugged a hose seconds after running the engine it did not spray everywhere

I'm sure someone will be along with the correct procedure and settings, as mine is at home somewhere

So - is he measuring resistance (ohms) or volts..

If the value starts at around 0.32 volts and rises smoothly to 4 or more.. then it's fine.

A low speed misfire can also be a weak mixture - they don't burn so well without a lot of advance and the dizy does not give that until further up..

So - maybe an injector is knackered.. check the connectors are pushed home.. you can also remove them one at a time an see if the problem does not get worse (found it !!).

[gsx600]

I'll be measuring the resitance in volts As its easier in line - resistance of the pot compared to the volts coming out

[dickymint]

gsx600 said:

I'll be measuring the resitance in volts As its easier in line - resistance of the pot compared to the volts coming out

Paul - before you adjust it (if you do) make sure that the butterfly gap is correct ie. 0.003 - o.oo5".
Take the air intake hose off and clean any crap from inside that may be stopping the butterfly plate returning to its stop first. Many people adjust the throttle linkage stop to get a better tick-over which in turn knackers the TP setting.

Edited by dickymint on Thursday 6th September 18:20

[matt-man]

dickymint said:

gsx600 said:

I'll be measuring the resitance in volts As its easier in line - resistance of the pot compared to the volts coming out

Paul - before you adjust it (if you do) make sure that the butterfly gap is correct ie. 0.003 - o.oo5".
Take the air intake hose off and clean any crap from inside that may be stopping the butterfly plate returning to its stop first. Many people adjust the throttle linkage stop to get a better tick-over which in turn knackers the TP setting.

Edited by dickymint on Thursday 6th September 18:20

I did that...maybe thats my problem?!

[rev-erend]

dickymint said:

gsx600 said:

I'll be measuring the resitance in volts As its easier in line - resistance of the pot compared to the volts coming out

Paul - before you adjust it (if you do) make sure that the butterfly gap is correct ie. 0.003 - o.oo5".
Take the air intake hose off and clean any crap from inside that may be stopping the butterfly plate returning to its stop first. Many people adjust the throttle linkage stop to get a better tick-over which in turn knackers the TP setting.

Edited by dickymint on Thursday 6th September 18:20

Dicky - are you sure that is correct.

The later hotwire system has a tick over by-pass tract (I believe) and the butterfly is closed (again - I think).. so it's different to the flapper system.

Also - Paul has a 'Massive' 80mm inlet butterfly .. sounds like some one has been busy with the TIG in the past.

[rev-erend]

pwd95 said:

Yep flapper, can't give you the history of the vacumm, thats how it came. Runs fine. It has an adjustable ecu which I was going to look at fiddling with but after speaking with one of the engine builders who was at JE when my engine was built, he said the engine would have been set up on the dyno and the ecu set for that particular engine. Add to that the fact that it gave 315 ft/lbs of tourque on the rollers at BBWF without any fuss, smoke or pinking tells me that it must be in the correct position.

PWD / Leigh,

Blanking off the AR is a trick .. it gives a bit more mid range punch.

Give it a try - the car drives like an animal like it..