3.5L V8 not engine braking smoothly

[I Love My Landy!]

G'day all!

My 3.5L V8 is not engine brake smoothly. It's a bit hard to explain but when i lift off the throttle and the revs start to drop, the motor seems to lurch which causes the whole driveline to clunk about, and the only way to stop it is to engage the clutch. It seems to do it more when the motor is warm and when running on LPG (hardly does it on petrol). I've recently reconditioned the motor but it was doing it before then as well.

Does anybody know what could be causing this? I've looked for vacuum leaks but can't find any. I've got old ignition leads (been meaning to replace them with Gasmaster leads) but even under load they only give a very slight misfire.

Thank you in advance!

Edward :)

[roverv8]

Hows your idle speed,
is it a little high when on LPG?

[I Love My Landy!]

Thanks roverv8.

No it isn't high. I've played around with the idling a fair bit and the problem still occurs no matter what the idling is set at.

Edward

[mike 90 RR]

I've recently reconditioned the motor
I've got old ignition leads .... they only give a very slight misfire.

Does anybody know what could be causing this?



Edward

Time to buy your Gasmaster leads?? ;)
What is the condition of your Drivetrain??

Mike

[I Love My Landy!]

Thanks mike 90 RR.

Yes probably. I was given the impression that i needed to use very high quality and very expensive ignition leads with my LPG motor (ie. magnecor, gasmaster), and this high price has prevented me from getting a set for a while, however i just called up a couple of well known Landy experts and they said to use cheaper leads and just replace them more often. If this is the case then i'll buy a set soon. Also i've had dodgy ignition leads on other cars that have caused a misfire under load, but never when engine braking.

The drivetrain is in pretty good condition. There is a little bit of wear on the axles but nothing out of the ordinary.

I don't think the problem is drivetrain related, it just feels as if the motor does not run right when engine braking which causes the whole car to lurch to and fro and causes the drivetrain to clunk about.

Edward

[mike 90 RR]

I don't think the problem is drivetrain related, it just feels as if the motor does not run right when engine braking which causes the whole car to lurch to and fro and causes the drivetrain to clunk about.


Interesting description of problem ...


BTW ... What model is your ride?? ... Are we talking carby with standard dizzy with points ... or EFI & electronic dizzy

[I Love My Landy!]

1984 3.5L V8 County. Carby with original dizzy but with lumenition electronic system. The dizzy has had new weights put in specifically for LPG. The vacuum advance has been disconnected and i'm now running around 14 degrees advance timing.

Thanks!

Edward

[mike 90 RR]

The vacuum advance has been disconnected

Funny ... My first reaction to reading, the start of this thread, was to tell you to check the vacuum advance for working, and that it is hooked up to the proper inlet of the manifold

So your dizzy is modified ... So who knows what it's doing ....


Process of elimination .....
I would borrow a "known" second hand / ordinary Dizzy and give that a go .....



BTW ... If you recon'd the motor ... Did you do any mods to that also??


Mike
:)

[I Love My Landy!]

Apparently LPG likes to have a lot of initial advance with a low maximum advance, so the dizzy has been modified so that it has a maximum advance of only 28 degrees. Therefore I’m pretty sure that the vacuum advance is not necessary.

I’ve previously done some minor modifications to the motor, including a stage 2 camshaft, shaved the heads, port and polished the inlet manifold and did a few other little things. When I reconditioned the motor i basically just gave the motor a freshen up and replaced the stage 2 camshaft for a more standard (torquey) cam.

Edward

[mike 90 RR]

Apparently LPG likes to have a lot of initial advance with a low maximum advance, so the dizzy has been modified so that it has a maximum advance of only 28 degrees. Therefore I’m pretty sure that the vacuum advance is not necessary

... Nothing wrong with running the modified version ... just that you do have a problem, and the trying of the Spare standard Dizzy, especially when running Petrol, will help eliminate it as a problem




I’ve previously done some minor modifications to the motor, including a stage 2 camshaft, shaved the heads, port and polished the inlet manifold and did a few other little things. When I reconditioned the motor i basically just gave the motor a freshen up and replaced the stage 2 camshaft for a more standard (torquey) cam.

And the above bit sheds a little light .... :Thump:
And did you take advantage of the "adjustable timing chain gears" ... and advance the Cam ??

Mike

[I Love My Landy!]

Thanks again mike 90 RR!

Yeah i'll see if can source a different dizzy to try.

I used a Rollmaster double row timing chain, but with advice from some Landy experts i did not advance the cam.

The problem started before i reconditioned the motor, and the problem did not get better or worse after.

Edward

[PLR]

G`day Edward

I`d suggest you have a look at the vacuum unit and see if your leak is not a diaphram hole/split from running full vacuum , you know suck on the pipe and see if it holds your tongue .

If the vacuum was hooked up this way prior and the problem was there , I`d suggest if the unit works , plug the full vacuum hole and hook the pipe up where it gets partial vacuum , near the butterfly .

The vacuum advance normal works at times of partial throttle and overrun etc when your problem is occuring .

I`d suggest if it has a miss you fix it

We have 2 V8 RRs on petrol/lpg and have found that Bosch super sports leads do the job without trouble .
Infact with you County other than the coil lead you can use leads that suit both Windsor and Cleveland V8 Fords of approx 1970 - 84 , they will often be found cheaper than Rover .

If none of that helps the carbs would be where i`d look next , does yours still use the popet valves on the butterflys ?
Does yours still run twin carbs and what type of setup gets the lpg in , ring , gas carbs ? .

Does it backfire/pop on over run and have you check the exhaust for leaks/holes ?

Cheers

[I Love My Landy!]

Thanks PLR!

I’m not actually running a vacuum advance unit atm. I’ve removed the hose and plugged the hole.

That’s good to hear that you have not had any trouble with your Bosch super sports leads. I was looking at these at Supercheap Auto the other day and the price seemed right. I’ll just have to look for a set for a Windsor or Cleveland!

I am running twin SU carbs with the ring for delivering the LPG. I’m not sure what you mean by ‘poppet valve’ though. Do you mean those temperature compensator things behind those cream coloured plastic covers?

Yes the car does pop a fair bit when engine braking down steep hills, but I presume this is just due to a lean LPG mixture? (I sometimes run a tad leaner to save fuel). The surging does not occur at high revs, it only really occurs when you are slowing down for a very tight corner (generally when you are engine braking in third and about to negotiate a tight corner that would see the revs drop to around 1200 rpm). I have played around with the mixtures and it still surges when it's been richened up.

The exhaust does have some leaks in the spots where the extractors join to the bottom sections of the exhaust (couldn’t find the exhaust cement on the day of fitting!). How would this cause problems?

Thank you!

Edward

[bee utey]

I suggest trying a little less advance, I usually set the V8's at 10 degrees. Your advance curve might still be a little quick, use your timing light to see how much advance you get by 1200-1500 rpm. Most dissies I modify to LPG get the primary (weak) advance spring tightened up by 30% or so, and the slack on the secondary spring reduced by 70%. The Bosch leads are good, they are not usually the issue with your running problem. The popping in the exhaust will disappear when ALL your exhaust leaks are fixed. The extra air is what leans off the LPG in the exhaust. Lean => fast flame speed.

[It'sNotWorthComplaining!]

I spent the dollars and initially bought the Magnacore leads, only to find them perish at the plug ends from heat after about 2 years, the casing over the core disintegrated.
I replaced them with Bosh ones and have no problems or probs on LPG

[I Love My Landy!]

Thanks bee utey and It'sNotWorthComplaining!

I'll retard the timing to 10 degrees and give it a go.

I'll also look into getting a set of those Bosch leads. I priced a set at Supercheap Auto and they weren't that dear at all!

Thank again everyone!

Edward :)

[350RRC]

I can vouch for these Bosch leads as well. Have had them on for 60k km with no probs. Seem to maintain quite low resistance. Think I paid about $6 per lead on special at SC.

cheers, DL

[bee utey]

Incidentally the Bosch leads come with a 100,000km warranty, fine so long as you remember where you put the receipt!

[I Love My Landy!]

I've looked into the Bosch leads and they do look good, but they have 3500-7000 Ohms resistance per metre. I was looking at Eagle LPG leads which are just a little dearer, and they only have 1300 Ohms resistance per metre and still have good RFI suppression. Might look into these a bit more.

Thanks again!

Edward :)

[350RRC]

I've looked into the Bosch leads and they do look good, but they have 3500-7000 Ohms resistance per metre. I was looking at Eagle LPG leads which are just a little dearer, and they only have 1300 Ohms resistance per metre and still have good RFI suppression. Might look into these a bit more.

Thanks again!

Edward :)

None of mine are over 5 whatevers after 60k kms. 10 is about the limit from memory. Don't waste your money. I was going to Magnecore or Gasmaster but there is really nothing to be gained. (apart from 'qudos')

Mine are just draped across the top of the boat anchor, no separation, no probs.

cheers, DL

[I Love My Landy!]

Thanks 350RRC.

I've got a set of Bosch leads on order!

Cheers!

Edward :)

[bee utey]

I've looked into the Bosch leads and they do look good, but they have 3500-7000 Ohms resistance per metre. I was looking at Eagle LPG leads which are just a little dearer, and they only have 1300 Ohms resistance per metre and still have good RFI suppression. Might look into these a bit more.

Thanks again!

Edward :)
The reason I went to the Bosch leads is because the lower resistance Top Gun leads I was using before were giving me some trouble with erratic low speed running. Anfd I found the Bosch boots stay waterproof for much longer.
Low resistance is like too stiff springs on your suspension, there is an optimum value.