The V8 Owners Forum -

Hi all, I've finally got the car on the road after a 6 year build took it out for its first true run the engine (3.5 EFI with a 3.9 Cam) starts up fine and accelerates really good but when i back off to cruise, the engine starts to judder and gets quite bad and the only way to stop this is to drop down a gear and start accelerating. Anybody know what the cause of this would be?
Cheers Paul

Air leak?

Chris.

Hi Chris, been through all the hoses all are brand new and all are secure.

Carbs - what type? Or injection - what type?

Is it the flapper EFi from a Range Rover?
If it is, you could try bypassing the overrun cutoff valve.

Chris.

Hi Chris, you were right it’s an air leak multiple leaks!
The centre bolt securing the plenum down air is being sucked in there, also the throttle spindle is really bad!
Stripped it all down and have ordered new seals and throttle spindle bushes from Rimmer Bros.
Anyone know how to replace the bushes? Is it an easy job or do I need to get an engineering co to do it?

Cheers Paul

If you have the right tooling, the bushes will be relatively easy, if fiddly.
You will need a press to push the old ones out and new ones in and then a set of adjustable reamers with pilots to ream the bushes and keep them straight at the same time.

I'd be surprised if a minor leak caused juddering at speed, as it doesn't effect the mixture in the same way as a carb car. A leak like that usually just results in a fast idle.

Oh don’t say that Dave, thought I’d found the reason. Your right with the fast idle though.

You still havn't said what type of injection. If a lot of air not metered by the AFM is getting in, it might well cause problems further up the rev range. If you have fixed the leak at the plenum seal, try appling some thick grease to the throttle spindle to seal it temporarily. If the idle come back to normal you'll have the answer.

BTW, on worn ones I've seen, it's sometimes just mainly the spindle which wears.

Hi dave sorry forgot to mention its the early 4cu ecu with the flapper afm.

It could also be the Airflow Meter making the engine run lean.

Chris.

Hi guys here is the latest update whilst renewing the throttle seals I also checked the overrun cutoff valve, this wasn't opening due to a blob of gasket sealant!
Also changed the AFM with another unit,comparing the two unit side by side there are a couple of things wrong with the old unit, firstly there is a small spring missing on the rear of the armature. secondly the butterfly is a lot harder to open with the new unit, which leads me to believe the old unit has has been tampered with.
All put back together and wow what a difference so much smoother to drive!
Still had a fast tick-over at 2000 rpm but that was because the throttle butterfly wasn't sitting shut, that was an easy fix.
Now running at 1500 rpm.

The throttle butterfly should be totally shut at idle, and the idle speed is set by the bypass screw next to the butterfly.

Chris.

My Land Rover manual on this EFI says the throttle butterfly should be set to a clearance of 0.1mm (between disc and body) when closed.