Thread: 3.5 V8 Rough running > 80kms on LPG & replacement

Driving to work yesterday it ran a lot better and then I ran out of gas 1/2 way. Drove on petrol the rest of the way and filled up on the way home. Then it ran like a dog. I was lucky to get it about 90kph at times with the car jerking around. When I tried to floor it under 80kph it was under powered but there was no missing but when under load from 90 up it jerked and shuddered.

Then when I drive to work this morning, I start on gas and run the whole way. I bit of shuddereing here and there (still noticeable) but nothing like yesterday afternoon.

I just feel the mech wasn't too fussed to get to the bottom of the problem and decided the low comp was the issue....???

Is there anything else I can look at now, like timing, air restrictions, vaccuum, etc??

TIA

Originally Posted by StuRR80

Driving to work yesterday it ran a lot better and then I ran out of gas 1/2 way. Drove on petrol the rest of the way and filled up on the way home. Then it ran like a dog. I was lucky to get it about 90kph at times with the car jerking around. When I tried to floor it under 80kph it was under powered but there was no missing but when under load from 90 up it jerked and shuddered.

Then when I drive to work this morning, I start on gas and run the whole way. I bit of shuddereing here and there (still noticeable) but nothing like yesterday afternoon.

I just feel the mech wasn't too fussed to get to the bottom of the problem and decided the low comp was the issue....???

Is there anything else I can look at now, like timing, air restrictions, vaccuum, etc??

TIA

Sounds like poisoned plugs. They get a coating from running on petrol and this causes misfires. Not uncommon in my experience. My suggestion: new plugs, Bosch WR7DC or similar, run petrol only when the engine is completely hot and as little as possible, use premium unleaded when you do. Plugs should have white or light grey insulators when operating on gas. Any hint of yellow/brown and they are scrap.

Just a little side track - in my dual fuel 3.5 running Bee Utey's holden dizzy and electronic amp at 9 BTDC and mainly on LPG - I am using NGK BP6HS.

These plugs are showing a nice light tan colour with no oil etc and the engine seems to be running OK. Are these plugs OK?

Also Bee Utey - I want to get another ignition amp like the one you sent me last year as a spare - where can I get one?

Cheers

Garry

Originally Posted by garrycol

Just a little side track - in my dual fuel 3.5 running Bee Utey's holden dizzy and electronic amp at 9 BTDC and mainly on LPG - I am using NGK BP6HS.

These plugs are showing a nice light tan colour with no oil etc and the engine seems to be running OK. Are these plugs OK?

Also Bee Utey - I want to get another ignition amp like the one you sent me last year as a spare - where can I get one?

Cheers

Garry

Hi Garry
So long as the plugs are running well, stick with them. They are the correct heat range. IMO the problem with standard heat range plugs is they get hot enough to create a ceramic glaze of combustion products on the insulators, then they are stuffed.

As for your dissy amp, this was a genuine conversion kit marketed by Bosch in the 80's. My old (2000) Bosch catalogue lists a replacement module part number 9 220 066 005. Probably not available new any more. I know these are specific to the kits and are not interchangeable with other similar looking modules. The main advantage of this kit was easy reversal of the kit fitting to points, so all you need for emergencies is a standard Holden V8 rotor, points and condenser.

Another way to achieve spare parts is to remove the conversion and fit the innards of a Blue motor electronic dissy to your case. These were fitted to Holdens from 1981 to 1985 or thereabouts and are quite common on ebay.
Example: holden v8 electronic distributor (eBay item 250753048039 end time 16-Jan-11 23:04:59 AEDST) : Cars, Bikes, Boats
Then with a remote coil/amp set-up like the one I use you have a modern system with OEM spare part availability.

Actually saw just what you want on ebay, I think. Ask the seller what the number in his amp/module is:
http://cgi.ebay.com.au/Commodore-EH-...item19c22abb53

And ask him to look inside the cap and post a pic of the rotor. The rotor won't be any use to you but the pick-up should be...

Cheers

Originally Posted by StuRR80

He mentioned the oil could be from the rings but he also said it could be coming through the valves from the heads? Is there a way to "easily" check which way the oil is moving?

G'day Stu,

To test if oil is entering the cylinder through a worn valve guide, drive down a long hill and use the gears to engine brake the car (i.e. have the engine running at high rpm with your foot off the throttle). At the bottom of the hill give the motor a rev and check to see if any blue smoke comes out of the exhaust. If there is a bloom of blue smoke then oil may be being sucked into a cylinder through a worn valve guide when the engine is running under high vacuum. A bloom of blue smoke may also be apparent after idling the engine for a moderate time (like when waiting for traffic lights).

A constant stream of blue smoke whilst accelerating may indicate oil getting past the piston rings.

Even if you are burning a little bit of oil through worn rings or through the valve guides it is not necessarily a major cause for alarm, unless it is excessive.

Edward

Originally Posted by bee utey

Sounds like poisoned plugs. They get a coating from running on petrol and this causes misfires. Not uncommon in my experience. My suggestion: new plugs, Bosch WR7DC or similar, run petrol only when the engine is completely hot and as little as possible, use premium unleaded when you do. Plugs should have white or light grey insulators when operating on gas. Any hint of yellow/brown and they are scrap.

Thank Bee Utey! I'll give it a whirl. I wish there was someone in Brisbane who knows as much about these things as you seem to!

If I'm running Premium unleaded, I'll need to get the timing adjusted to suit?

I have an RPI dual timing box which I need to fit hook up to the distributor so will need to re-time it then anyway. I've never done the timing before but I'm willing to give it a crack. I'll grab a timing light from Supercr@p or Repco or somewhere and give it a whirl one day. I'll need one for my 109" at some point, anyway.

Originally Posted by StuRR80

I also noticed that the resistor/ condensor/ or whatever it is () i.e. a ceramic thingo with leads from the coil and somewhere else, moved around a bit which allowed one of the contacts to touch the mounting, which I'd imagine would earth it. Don't know if that makes any difference andI would have been doing it since I bought the car but I've zipped tied it into place anyway.

This is the ballast resistor, used to drop the voltage to the coil from 12v to 6v so that it is easier to start the vehicle while the starter motor is sucking juice from the battery. Both contacts would be live so yes, accidental earthing will not have been helpful.

Your coil should be one that is intended for use with a ballast resistor. Do you have a spare coil to swap over to see if it makes any difference?

While on the electrics, I would check that the connections to any solenoids on the LPG feed pipe and the mixer are good. Especially the one that switches out the petrol otherwise you will end up with a rough mixture.

What is your timing set at? LPG likes earlier ignition than petrol but prefers not to be advanced too much further again as the engine revs rise.

Also, I would keep the plug gap at 0.8 or 0.9 rather than closing it up. I used to use NGK BPR6ES but have never looked back after switching to BPR6EIX. LPG will reveal any inadequacies in an ignition system.

Lastly, are you satisfied the LPG running mixture is correct?

Originally Posted by LoveMyV8County

This is the ballast resistor, used to drop the voltage to the coil from 12v to 6v so that it is easier to start the vehicle while the starter motor is sucking juice from the battery. Both contacts would be live so yes, accidental earthing will not have been helpful.

Your coil should be one that is intended for use with a ballast resistor. Do you have a spare coil to swap over to see if it makes any difference?

While on the electrics, I would check that the connections to any solenoids on the LPG feed pipe and the mixer are good. Especially the one that switches out the petrol otherwise you will end up with a rough mixture.

What is your timing set at? LPG likes earlier ignition than petrol but prefers not to be advanced too much further again as the engine revs rise.

Also, I would keep the plug gap at 0.8 or 0.9 rather than closing it up. I used to use NGK BPR6ES but have never looked back after switching to BPR6EIX. LPG will reveal any inadequacies in an ignition system.

Lastly, are you satisfied the LPG running mixture is correct?

Ahhhhh! All these questions Chris....!! Unfortunalety, I'm not sure I can answer most of them though...

I just take it to someone who is "supposed" to know what they're doing and pay for the privilege! Although would prefer to know what to do and what to look for, myself.

I just had it tuned up (at least that's what I asked for) by a specialist carb & gas mech, so I "assume" he's set the mixture, timing, etc correctly (although everyone knows what "assume" did!)

I will check the Coil is supposed to work with a balast though and also the connections. With the amount of wire running in there, something may have come loose or just needs a clean.

You reminded me I did have an issue with a fuel solenoid cut-off a few months ago when I accidentally pulled the wire from the plastic casing. One of the guys at work tried to bodge a solder job to get it back on but maybe it's letting fuel through. I'll see if any petrol's excaping from there too.

Thanks for all the forthcoming help & tips guys