vanden plas efi running lumpy

[dave fordham]

hello everyone .ive just purchased a vanden plas efi manual.v8.goes like aa rocket my problem is that we replaced the air flow meter due to running too lean and meter fully adjusted but for some reason when we checked the timing the pointer is no where near the mark.its on the f of the before writing.if we put on the mark then runs badly.also ticks over very slightly lumpy,and prefers higher revs through the lower gears or when in traffic seems bit lumpy.pulls great,revs smooth and responsive.one final question its on a 85 does it need additive in fuel? thanks shall look forward to any replies.dave

[DaveEFI]

hello everyone .ive just purchased a vanden plas efi manual.v8.goes like aa rocket my problem is that we replaced the air flow meter due to running too lean and meter fully adjusted but for some reason when we checked the timing the pointer is no where near the mark.its on the f of the before writing.if we put on the mark then runs badly.also ticks over very slightly lumpy,and prefers higher revs through the lower gears or when in traffic seems bit lumpy.pulls great,revs smooth and responsive.one final question its on a 85 does it need additive in fuel? thanks shall look forward to any replies.dave

Another place for advice would be the SD1 club forum.

http://www.roversd1club.net/forum/default.asp

They'll often run rather better with more advance than the standard 8 BTDC, but did you check /set it with the idle below 800 rpm and the vacuum disconnected? it could also be the pointer isn't indicating the correct position - a TDC check might be needed. That's all assuming it has the correct dizzy in good condition.

As regards fuel, I run mine on Super Unleaded - the extra cost is justified by better performance and economy. Allegedly. But many do run on 95 octane. They don't need a fuel additive.

As regards it running weak, the plug colour often will show this as they run very weak at cruise. If it feels flat at low revs or when initially accelerating, it could be two things. The TPS provides the initial enrichment, and these are often worn, especially at the lower end of the track. They also provide the full throttle enrichment, but this part of the track is often OK. A new one is very costly - if you can find one - but the old can sometimes be repaired by opening it up and moving the wiper to unworn part of the track. Or can be replaced by a different design and adaptor plate

The AFM adjustment only effects the idle mixture and should be set using a CO meter (MOT station?) to 1.5-2%

IMHO, the most usual reason for an excessively weak mixture is low fuel pressure. It should be 36-38 psi with the vacuum disconnected. Not any lower. Check by disconnecting the feed to the cold start injector and insert a pressure gauge - you can adapt a tyre one. Low pressure can be down to a faulty reg, pump, or low volts to the pump. It should be getting 9 volts. Although if it is fine at high revs/demand likely just the reg. A non rising rate adjustable type (for turbo engines) is a worthwhile buy as many of the standard ones are set on the low side of acceptable. A rising rate one will work well performance wise but make the economy worse.

BTW, most VDP EFIs are autos. Has yours been converted to manual? If one of the very few factory manual ones, the club would love to hear from you.

[ChrisJC]

If the timing is nowhere near the pointer, are you definitely on no.1 lead? (passenger side front)

Chris.

[dave fordham]

thanks for replys from you both.we changed air flow meter as would only go to 1.0 on co at its best.still have to get back on machine to see what like knowl.sorry to say that the cars not the factory manual.shall check manually to see if pointer is in correct place for tdc .and yes did have timing light on no 1.any ideas about why likes to run with higher revs in lower gears would be greatly welcomed. thank you speak soon.hope to be able to add a few pis too.dave

[DaveEFI]

thanks for replys from you both.we changed air flow meter as would only go to 1.0 on co at its best.still have to get back on machine to see what like knowl.sorry to say that the cars not the factory manual.shall check manually to see if pointer is in correct place for tdc .and yes did have timing light on no 1.any ideas about why likes to run with higher revs in lower gears would be greatly welcomed. thank you speak soon.hope to be able to add a few pis too.dave

Forgot to add check the plug leads and that the lead runs are correct. If they aren't you can get cross firing. After market dizzy caps and rotor arms can cause problems too, I'm told.

Sounds like the original AFM needed a good clean. The adjustment just bleeds air past the flap.