Engine Idle Question

[wannaberacer]

I am looking at buying a SWB Nissan MQ Patrol that has had a EFI 4.1 Ford Motor bolted into the engine bay.

Part of my checking the condition of the engine was to look for blow-by by removing the tappet cover oil filler plug.

There was no visible blow-by, but when the plug was removed with the engine running, the revs dropped a lot and it was almost on the verge of stalling. It managed to pick the revs up a bit by itself, but was not idling normally. When the plug was put back in place the revs returned to normal idle.

Does anyone know what would cause this? Is it an indication that something in the motor is stuffed? I have not seen other motors do this.

Cheers

[chimpboy]

I am looking at buying a SWB Nissan MQ Patrol that has had a EFI 4.1 Ford Motor bolted into the engine bay.

Part of my checking the condition of the engine was to look for blow-by by removing the tappet cover oil filler plug.

There was no visible blow-by, but when the plug was removed with the engine running, the revs dropped a lot and it was almost on the verge of stalling. It managed to pick the revs up a bit by itself, but was not idling normally. When the plug was put back in place the revs returned to normal idle.

Does anyone know what would cause this? Is it an indication that something in the motor is stuffed? I have not seen other motors do this.

Cheers

I'm only guessing because I am not familiar with these motors, but could the tappet cover be hooked up to vacuum? Take the cover off => vacuum leak => confused computer => overfuelling or underfuelling => screwy idle?

Dunno, just a thought. I'm struggling to think of a scenario where the symptoms you describe would be a sign of a serious problem with the engine, anyway.

Jason

[-Scott-]

There is probably a PCV connection between the tappet cover and the air intake, to suck fumes through the engine and burn them. At idle there will be very little flow through this line. I'm guessing that removing the plug opened this line to atmosphere, allowing the engine to suck more air that way, which bypassed the air flow meter? or something like that. It took a little while for the computer to catch up, and it couldn't compensate for the extra air flow - hence not returning to normal idle while the plug was off.

I'm guessing here, but it sort of makes sense to me - I wouldn't worry about the problem you described.

I would worry about it being a Ford engine, but that's a personal thing.

Scott

[murcod]

From what I've heard before that's normal behaviour for the Ford 4.1 EFI. The whole engine is sealed from the atmosphere and if a leak develops (like you caused by removing the cap) then they run like sh*t.

NJ Ford do make some good engines- just not the Aussie 4.1......

[pcman]

as NJ SWB said its the pcv valve setup i only realised this after having mine idling badly for month when i chaged from a breather cap to blocking it off lol ive got a te cortina with 4.1 carbied but efi is the same engine

[zooki]

Everybody is right about the leak, it;s pretty common for them to stall when you take the dipstick out as well (doing the same leak thing) or if the O-ring on it is stuffed. Word of caution, if you ever have to replace any intake gaskets or the thin rocker cover gaskets, glue one side down with contact adhesive or the motor will suck them in