Misfire & Mechanical Noise....

[ben]

Help!-

 

KE30 with a 5K engine has had a misfire which has gradually been getting worse despite my best efforts for the past month. Misfires at idle, on acceleration and whilst cruising- at all engine speeds.

 

The 5K was rebuilt in 2003 and was converted to solid lifters in Jan 05 with no problems before or after.

 

Fuel delivery to 40mm Weber is good and all jets are clean- Float level is correct and I replaced the manifold gaskets in Aug last year. It does however run on after shut down. It has always done so, but is now worse, but it doesn't do it all the time...

 

Spark from the coil is good and if I pull the lead off any cylinder the engine drops that cylinder so they are all sparking. Timing is fine at 15 deg BTDC

Checked primary circuit and is all good. Mech advance works fine too with no excessive play.

 

Hooked up a Vacuum gauge which showed a misfire, fluctuating between 18 In Hg and 7In Hg, so definitely not a manifold leak.

 

The mechanical noise sounded like it might be a chewed lifter so I have pulled them out and they are all fine with only negligable wear. Valve clearances are the same as they have been since the solids went in at 10 thou inlet and 12 thou exhaust. Valve springs are double and again are all good.

 

Compression check was fine with 3 at 225psi and 1 at 220psi and all held the pressure for a good 20 seconds before showing any leakage which was very slow.

 

Could it be the Weber? and would that cause a mechanical noise? Not likely I know...

 

Maybe a worn Valve guide or a burnt valve???

 

I'm a bit stumped for what to do next, just want to make sure before a pull the head and it ends up being something else...

 

Would appriciate any assistance, thanks.

:y:

[Felix]

are you sure it is not a vacuum leak? at one stage i had a miss which i ended up tracking down to a cracked inlet manifold on one of the intake runners. think it was caused by the inlet manifold flange being slightly different in thickness to the extractor flange, and overtightening of the manifold nuts. the vacuum fluctuated similar to how you described.

 

what sort of solid lifters are they, with what pushrods? i had a problem with the valve clearance adjuster screws on the rockers hitting the inside of the rocker cover when i converted to solid lifters in my 5k. i initially thought i had a bigend bearing problem until i worked it out.

 

15 degs is a bit of advance does it still run on with less advance? not lean at all? have you tried an air/fuel meter or something on it to get an idea of the actual mixtures?

 

that is a lot of compression you got for your test. what sort of cam is in it, and did you work out what the static compression ratio should be? if you have too much compression you will have a big problem trying to fight off detonation/pinging unless you back the timing way off, which makes an engine run flat.

 

a burnt valve would be indicated by low compression on one cylinder.

 

not sure if i can help with your problem, but a few things to think about/try anyway....

[Jared]

yeah i was gonna say vacuum but sounds fine when did u give it a good service last and what fuel are u running... fuel could be the problem with the run on is the exhanuse manifold on tightly as they can have a tendancy to become slightly loose theres many other things to go on ill just check my manual as well see if i can work out anything else u sohuld check

 

 

ok for misfire at idle it says to check ...

 

spark plugs, dissy cap and points ... i have a new one sitty around u can have, hightension wires, idle mixture with the run on sounds like it could be running rich, dissy motor, or moisture on sparkplug leads, spark plugs

 

 

engine missing at accel...

 

dissy, cap points ect

spark plugs dirty warn ect

carby accel.. discarge pump blocked or deffective

coil or capasitator faulty

incorrect timming (should be standard 10dtdc)

pitted valves burnt

 

miss fite at hight speeds

 

dissy again

sprakplugs again

carby acc pump

excessive cam wear

 

... hopefully this helps if u need any help with it I'm more than happy to help out 0431768038 or if ur on msn [email protected]

[ben]

I think I have it sorted, sort of...

If I idle it at 1500 rpm and pull the leads off you can notice a difference in the no. 4 cylinder. All the other cylinders drop to 1200 but no. 4 dropped to only 1300-1350. So it would appear that the problem lies here.

 

The PCV valve is on the No.4 inlet too... funny thing that. I disconnected that and it didn't run any better just sucking clean air or if i blocked the port and leaned the mixture.

With the PCV port blocked off and mixture leaned and idle at 1500rpm i reconnected the vacuum gauge and this time got a reading i can make some sense of.

Steady vacuum at around 20 in Hg at 1500rpm with an intermitent drop to 15 in Hg and back again. A sticking valve, more than likely in the No4 cylinder!

 

So i will pull the rocker gear off again and pull the valvesprings off no 4 and check the valves and spray liberally with Nulon carb and throttle body cleaner AKA the best carbon disolving agent known to man.

 

The Motor was built in 2003 by Patterson Performance in Brisbane ( see latest Street Machine Mag for details). Has been balanced and blueprinted with lightweight racing pistons- I can't recall the Name but the next set up was a set of Kawasaki Racing motor cycle pistons at $1400 bucks, mine only cost arount $800. Had to to be dished to keep compression down anyway.

 

Runs about 10.5:1 compression with 225 PSI per cylinder and consumes only 98 octane optimax with 15 deg of mecahnical adv at idle and about 32 total all mechanical.

 

Cylinder head is a 5K with lightweight oversize stainless valves and Ford Laser retainers and collets- Better than stock K motor stuff. Runs 96lb double valve springs from Performance springs and a stage 3 Camtech solid Cam with Datsun A12 pushrods and 4K rockers machined to fit without hitting anything and lightweight Chevy solid lifters. Cam Specs are as follows:

 

Inlet lift is 0.264" and exhaust is 0.266" with duration at 0.050" of 220deg inlet and 223deg exhaust.

Head has been ported and polished on a flowbench, again can't remember figures, sorry.

 

Running a single DCOE 40mm sidedraft Weber on a Redline Manifold with the usual extractors and the rest.

 

It was dynoed when built and on the particular dyno they used it pullet off 89hp at the wheel at 7500rpm or 10hp less than the stock VK V8 that went on after it. I asked what they reved it to and the reply was, and I quote-" don't know, your tacho stopped at 8!"

 

I know the bloke who built it used to built Ford laser engines for 1 Litre sprint cars that would make 200hp at 11 grand.

[ben]

Cleaned all the valve guides with carby cleaner and then I got to the last valve....

 

Was about to put the spring back on the number 1 inlet when i felt air rushing out of the brake booster vacuum port in the manifold.

 

Turned off the compressor and emptied the cylinder, pushed the valve open and turned it around on its seat and pressurised the cylinder again. With the valve closed a steady stream of air was still escaping back into the manifold.

 

The more i turn the valve around and work it against the seat the better it seams to seal as now there is only a small amount of leakage past the valve.

 

The question is whether or not i can be bothered to pull the head off and grind the valve or whether i can get away with a clean for the moment....

 

I also intend to fit to fit an oil catch can as the no4 cylinder was very oily ( PCV vacuum from that intake runner).

Will the system scavenge ok if i just feed straight from the rocker cover to a catch can without the PCV valve and not plumbed back into the manifold.

 

If I go that way should I consider removing the oil/air separator from inside the rocker cover?

 

I know that legally only a racecar can vent to the atmosphere if the car already has a PCV system fitted.

 

Oh well, back to fiddling with the car....