Base Idle problem Griffith 500

[Loubaruch]

Although the car is now running OK I continue to have problems setting the base idle.
Initially the car would not idle at all until the air bleed hole in the Plenum was given a thourough cleaning. With the feed to the idle motor blanked off the maximum revs/minute only reaches 300 even with the adjuster fully out.

The timing has been checked and is spot on at 12 BTDC. Thinking the air flow maybe impeded by the filter (new) or elephants trunk I disconected the filter but it made no difference the maximimum revs still 300 rpm. Any thoughts? I did wonder if the plenum casting was maybe faulty and the air bleed passage is a bit restricted, not an easy thing to check!

[Johno]

Did you try to check the air bleed passage? Maybe with fluid, water or thin oil.

Also, have you checked the other pipes/air sources to the plenum/trumpet base, carbon can, servo and oil breather? All of them are in the system, so it should balance across all of them. With the throttle closed it’s quite a vacuum and should be able to get air from all of these sources. One way valves etc. which can all cause issues.

Probably simpleton thinking, I’d want to check all of those before worrying about the filter and induction hose.

[Belle427]

I can't think of anything else apart from the throttle disc blanking the air bleed hole but I cannot see that personally.

[blaze_away]

I agree with johno, go check all the crank case ventilation (CCV) hoses that run into the plenum, especially the short small bore hose passenger side that tees off the main CCV hose. This I beleive has a Non-return valve in it, maybe fitted wrong way round or blocked. Check the other hoses are clear eg carbon cannister hose, brake servo hose.

Also check/clean the rocker cover flame trap, I believe this is also a oneway valve.

Edited by blaze_away on Sunday 13th July 15:46

[Loubaruch]

Thanks for all the suggestions. I perhaps misunderstand the air flow but if either the Brake servo, the crank case breather or the charcoal cylinder feeds are leaking air would that not introduce more air into the plenum and increase the revs. The Charcoal cylinder valve I believe only opens at higher revs not at idling so that should be shut, similarily the brake servo should be sealed not allowing air but the crankcase breather is a mystery maybe that does need to be free to allow some air in.

Cheers

[blaze_away]

Loubaruch said:

Thanks for all the suggestions. I perhaps misunderstand the air flow but if either the Brake servo, the crank case breather or the charcoal cylinder feeds are leaking air would that not introduce more air into the plenum and increase the revs. The Charcoal cylinder valve I believe only opens at higher revs not at idling so that should be shut, similarily the brake servo should be sealed not allowing air but the crankcase breather is a mystery maybe that does need to be free to allow some air in.

Cheers

Thats correct but if any of those hoses are blocked then it may indicate others getting crap and potentially blocked.

[Johno]

blaze_away said:

Loubaruch said:

Thanks for all the suggestions. I perhaps misunderstand the air flow but if either the Brake servo, the crank case breather or the charcoal cylinder feeds are leaking air would that not introduce more air into the plenum and increase the revs. The Charcoal cylinder valve I believe only opens at higher revs not at idling so that should be shut, similarily the brake servo should be sealed not allowing air but the crankcase breather is a mystery maybe that does need to be free to allow some air in.

Cheers

Thats correct but if any of those hoses are blocked then it may indicate others getting crap and potentially blocked.

This . The servo and carbon can are one way valves, or at least carbon canister is operated under certain conditions. There also a restrictor I think in the CCV system.

It’s about making sure everything is operating as it should, then retracing your steps. It becomes all about 1 issue until you realise it’s nothing to do with it.

I chased an air leak on my old S for weeks and weeks and weeks, Turned out the servo had rotted and it had a small hole at the bottom, which you couldn’t see, bingo…. All sorts of shenanigans with AFM s and all sorts. It was a basic element of the system.

Edited by Johno on Sunday 13th July 21:20

[Belle427]

An air leak generally raises the rpm, this is a case of not being able to get enough air.
My limited knowledge is that the air enters either through the throttle plate, small bypass hole and stepper if all is well.
Maybe if the throttle plate is not adjusted correctly that could be an issue, not sure why it would have changed though.
Don`t think there is an official adjustment procedure for this, think it is set slightly open so it does not bind, may be that the tps percentage on rovergauge would be a good indication of its position.

[Loubaruch]

Many thanks chaps will look at these areas, gosh Belle you are up early!

[Belle427]

5am most days with a hyperactive 9 year old!

[Loubaruch]

After checking all the hoses into the Plenum all were clear except the inlet/outlet breather on the nearside rocker (see pic) apparently if blocked it can cause the rear crank seal to leak which it has been doing for a while.. A service item that has been overlooked by me as its under the accelerator bracket. The bleed hole under the filter is only 1mm diameter so is easily blocked. A new filter was made from the sponge part of a sink scourer almost identical to the original.

The other engine breather on the off side rocker cover enters the plenum before the accelerator plate so I doubt whether even if blocked would affect the base idle unless it was actually sucking. TBC

.

[blaze_away]

Loubaruch said:

After checking all the hoses into the Plenum all were clear except the inlet/outlet breather on the nearside rocker (see pic) apparently if blocked it can cause the rear crank seal to leak which it has been doing for a while.. A service item that has been overlooked by me as its under the accelerator bracket. The bleed hole under the filter is only 1mm diameter so is easily blocked. A new filter was made from the sponge part of a sink scourer almost identical to the original.

The other engine breather on the off side rocker cover enters the plenum before the accelerator plate so I doubt whether even if blocked would affect the base idle unless it was actually sucking. TBC

.

I forgot to mention that one, good job you found it. Let us know the outcome and send me the logfile and I'll let you know what effect its had.

[Johno]

Loubaruch said:

The other engine breather on the off side rocker cover enters the plenum before the accelerator plate so I doubt whether even if blocked would affect the base idle unless it was actually sucking. TBC

Except the T piece section, which feeds into the plenum base, after the throttle plate. I seem to remember there's a restrictor in the T piece and I'm miles away from my car to check. There would be a vacuum from the plenum base and if the restrictor was blocked ..... So I'd check that as well.

[Loubaruch]

Good call, it was clear when I checked. I will run some Log files Thanks Frank.

[Loubaruch]

Started to run some RG idling Log files to compare a Chinese MAF with a known good one from Jools.

The Chinese MAF run went smoothly although the car was very warm when finished with fans running continously.

Changed to the Jools MAF and the car refused to start making a metallic sound in the Plenum area, it would not even fire.

Changed back to the Chinese MAF and the same thing, not even firing and nasty metallic noise as the engine turned over.


Let it cool down and the car started with some metallic noise that quietened after a short while. I suspect that either the ignition amp or the coil failed in the heat but cannot explain the clacking noise maybe a very dry tappet.

Will try again tomorrow with the known good MAF to see if Frank can spot any differences.

[Loubaruch]

Before further checks the base idle could only be set to about 300revs irrespective of the bleed nipples position so:

Checked timing spot on at 12 BTDC

Checked all Plenum hoses and connections and found a blocked filter on the engine breather. Renewed the filter, cleaned all hoses but all were clear anyway.

Took the Plenum off again and with a Boroscope checked that the base air idle bleed pasage was completely clear, confirmed that cleaning brushes entered the plenum interior, no more deposits could be removed with carb cleaner it ran completely clear.

Started a fresh run and after idling to 90 ( fans running) blanked off the idle valve and attempted to set the base idle again, it would not even start this time without throttle, so things are worse than before the checks.


Any ideas? I am completely baffled.

Ps. anyone want to buy a Griffith 500 with a newly restored chassis etc.

Edited by Loubaruch on Tuesday 29th July 20:59

[Johno]

Did you check the TPS results on RG?

Vacuum advance connected and working?

Straws, grasping