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WOOHOO - aw crap


Shackleton
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Well after diagnosing the fuel pump problem as a secondary earth running through the pump bracket to work in tandem with a rubber mounted tank and subsequently realising that I had also reversed the polarity - but toasting a starter motor while trying to pump my fuel tank full of air rather then pump fuel out of it - I STARTED THE 3.9 - YES!

But it runs like a big bag of wet poo.

Could I have second opinion - when it fires initially it jumps up to god knows how many revs but maybe 1500rpm and after maybe 5 or 6 seconds slowly returns to a normal idle???

Then about midway up the revs but by no means at the same place every time it splutters and the power comes and goes intermittently. It seems to get over it at about 70mph but it's still not confident if you know what I mean.

At first I thought maybe there was something loose and it was happening as I went over bumps but no thats not it.

Any ideas?

EDIT; oh and it's smooth as a babys arse when not under load. As in I can rev it at standstill and its sweet.

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Welcome to Hotwire EFi...

My not-so-informed guesses would be:

- Ignition (specifically amp or vacuum advance) but also check the basics - cap, rotor, HT leads

- Airflow meter (not sure what you can do with it, try colourful language)

- Throttle position sensor (probably needs to be set at a specific voltage)

- Fuel pressure regulator (is it working, is it connected to a vacuum feed)

- Idle stepper motor (back of plenum) although this is to do with the erratic idle not the poor performance.

Failing that, are you parked near any mystical points of energy, perhaps you've got it at a funny angle to some nearby ley-lines or you need to put some bonsai trees on the dashboard to align the flow of Chi?

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Could I have second opinion - when it fires initially it jumps up to god knows how many revs but maybe 1500rpm and after maybe 5 or 6 seconds slowly returns to a normal idle???

Mine goes to maybe 1200 rpm (I'll check tonight) but only for a couple of seconds, I always assumed this was by design? IIRC I think it is controlled by the air bypass valve that seems to open up when starting. If there is a problem with this then (in my case) the symptom is intermittent high idle speed (read anything from 1500 to 3000 (!!!) rpm) often (but not always) after a run. Blipping the throttle would sometimes clear it. The cause is the valve not closing/seating correctly. After months of repeatedly removing and cleaning it (which would fix it for a few days) I finally bit the bullet and bought a new one (£50 I think :( ) and that fixed it. However during all this time the engine was fine under load so I think you might be able to exclude this (expensive) little beast...

Then about midway up the revs but by no means at the same place every time it splutters and the power comes and goes intermittently. It seems to get over it at about 70mph but it's still not confident if you know what I mean.

It takes a fatter spark to ignite the mix when the engine is under load...

IMHO FridgeFreezer has it covered : - Ignition (specifically amp or vacuum advance) but also check the basics - cap, rotor, HT leads - but just to add support to this: In my past experience a good cleanup and checkover of all of the above has nearly always sorted problems akin to those described.

Good luck!

Rog

Oooh - just realised - I can't check mine tonight, I've got the tank out! Silly me :D

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Welcome to Hotwire EFi...

AAAAAAAH!

Fridge - I'm rooted in the Tao so the force of the earth supports me, like the fire I also need the water, like the mountain I need the storm - err I don't know where I'm going with this :lol:

Right out of all those things it could be the Amp as I was f*&king with it in a major way, it could be the leads but it just doesn't feel like them if you know what I mean and it could be the vacuum to the stepper.

All the rest I reckon is in good order and/or has also been through a decent clean up during the build.

RE the idle I'll wait until my uncle returns from his new knee op. and I'll compare startup with his immaculate Vogue SE.

Thanks fellows, ,let the head scratching and colourful language begin! :rolleyes:

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- Airflow meter (not sure what you can do with it, try colourful language)

Unplugging the airflow meter will force the ECU into 'limp home' mode. Will tend to idle high, not run as well as normal and be on the thirsty side (but nowhere near as bad as you're describing). It won't pin the problem to the airflow meter as going into limp home could mask a problem with another sensor, but it will tell you whether your problem is fuelling related. So far as I know the only reliable test for the airflow meter is to swop it out for a known good one (see if you can borrow your uncles :) ).

My money's on ignition too, though.

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Hmm the vacuum unit on the distributor. There are two little pipes sticking out of it for vacuum hoses. One on the back and one on the front. When I got the 3.9 the front one wasn't connected to anything?

I now have the back one connected to the outlet on the top of the plenum neck, the front one is connected to the left (O/S) side of the lower plenum - technically the top of the ram housing. Is this alright?

I found the coil lead to be fecked at the coil end so I cut it back and re wired it but wasn't happy so replaced it with a plug lead from the 3.5 carb lump. Did I do bad? :D

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I would expect the back pipe on the vac advance to be connected to manifold vacuum (the plenum) and the front to either be open to the elements or blocked off. If you connect it to another point (you have connected both side to manifold vacuum) then you will have incorrect, or in your case NO, vacuum advance! :blink:

By jove, we could've found it!

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The advance stub is the one facing away from the distributor. The retard goes to the other one where fitted although this was only used, I assumed, for detoxed carb motors.

My 3.9 has been set up like this for years - I do hope it's not wrong! :blink:

P1030809%20(Medium).JPG

Rog

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wuh?

OK will do that then - and 'this bad boy' seems to be going to the little heater ball cock job on yours - I have it on the front of the vacuum unit. Best just block that off then seeing as I am using my original heater?

Been thinking more about the whole problem. Are spark leads and the coil lead different. As in is the coil lead designed to carry more load? I'm using a plug lead from the old 3.5 for the coil on the 3.9.

post-1811-1164784923_thumb.jpg

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wuh?

OK will do that then - and 'this bad boy' seems to be going to the little heater ball cock job on yours - I have it on the front of the vacuum unit. Best just block that off then seeing as I am using my original heater?

Been thinking more about the whole problem. Are spark leads and the coil lead different. As in is the coil lead designed to carry more load? I'm using a plug lead from the old 3.5 for the coil on the 3.9.

'this bad boy' is indeed going to the ballcock - dunno what that thing is... is it something to do with the heater then? (I used to have an XJ6 that had vacuum operated heater controls - is this the same?)

I don't THINK that king-leads are any different to normal spark plug leads (no doubt someone will KNOW the answer though) - in terms of load it only carries the same as a plug lead - just 8 times as often! :)

Rog

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