Slow response from 3.9 v8 rover

I've got a 3.9 that I have just converted to have a hotwire system with lambda's from not having them at all, but with both systems the engine was very slow to respond to any sharp throttle input, it seems to not hesitate or bog but just sit there idling for a second or so then pick and rev like it should.



Any ideas what the problem is?



I know it's not the injection system because that's new and I've put it on rovergauge diagnostic, and there's nothing irregular. So could it be the ignition, I know the timing is right because I did that I little while ago.

have you checked the timing?

As mark says, timing. It sounds like retarded valve timing to me though. Have you had the engine apart?

I haven't had the engine a part, but it came out of another car which it worked fine.

I have noticed that it does backfire through the exhaust when I back off the throttle. I have checked the advance mechanism and it seem to work.

I have also noticed if I put some extra advance at idle say to 15deg then it seems to improve its performance. Is this common should I just keep advancing it until it stops improving and leave it there.

RangeRoverMad said:

I haven't had the engine a part, but it came out of another car which it worked fine.

I have noticed that it does backfire through the exhaust when I back off the throttle. I have checked the advance mechanism and it seem to work.

I have also noticed if I put some extra advance at idle say to 15deg then it seems to improve its performance. Is this common should I just keep advancing it until it stops improving and leave it there.

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just make sure it don't start pinging

That's what I'm concerned about.

wont hurt if its only a bit for a few secconds till you pull over and adjust it, just dont run it like that

RangeRoverMad said:

I've got a 3.9 that I have just converted to have a hotwire system with lambda's from not having them at all, but with both systems the engine was very slow to respond to any sharp throttle input, it seems to not hesitate or bog but just sit there idling for a second or so then pick and rev like it should.



Any ideas what the problem is?

Click to expand...

1: Check your vac advance unit.
2: Have you got the correct tune select resistor for your set up?

I've got the correct tune resistor, white for a lambda set up, I have a green one which seemed to improve the backfire symptoms but was still slow to rev.

I'm not totally sure about the vacuum advance, I will check later today.

Could be a bad o2 sensor, try taking the dizzy cap off and sucking like a 10 dollar hooker and see if you can get the rotor to move. It's not likely to be the vac advance cos that only works on part throttle so when your foot is to the floor it wouldn't be used. You could also check the resistance is the same on the 2 sensors.

I've checked the distributor, and it does advance, the backfire in the exhaust and slow pick up seems to be cleared if I run the ignition timing is set at 16deg BTDC.

Just a quick question, on the crank damper on a serpentine v8 where the timing marks are written, at about 20 deg BTDC there is a slot taken out of the damper, with some white paint in it, So I'm wondering whether that is the actual timing slot.

Any ideas what it's for?

6 degrees btdc is std the running better when advancing it it just making real problem seem less ,

Its possible that the timing mark is wrong, an easy way of seeing if its close is put a stick like object down the spark plug hole and turn it by hand and try find TDC on piston 1 and compare. just make sure not to drop **** in the bore, and make sure you on the right part of the cycle.

What the eggspurts above said! Basically, don't assume. You're assuming it is correctly timed both on the ignition and the valves. How do you know the chain hasn't slipped or the pulley hasn't spun? If going too far advanced seems to make it run better then there's something wrong, so check and double check.