Power drops when put foot down

[dwhitaker]

I hope someone can help me here. My 98, 40,000 mile, serp 4.0 is not a happy bunny after its longer than usual layup due to waiting for me to fit a new clutch. Was fine before. Yes I know I should drive it more.

At about 4000 revs when static, or when I put my foot down, even a little, while driving, it misses like buggery and the power drops right off. Really embarrassing if you try and overtake someone.

Fuel was really low (but not yet run out) and I've refilled it since, so I had thought it might be that I'd sucked up some gunk in the fuel filter, but fuel pressure testing all checks out so not that.

I've been looking at timing, with the vac advance connected it seems to respond correctly, but with the vac advance removed, there is about an inch of movement of the timing line, probably about 15 degrees but difficult to be precise.

There's nothing obvious with the rotor arm and disti cap.

I have a new coil, because the old one had leaked early last year, but not fitted that yet, is it a possible culprit?

[Plan B]

Have you hooked up to Rover Gauge? Good first step for a diagnosis.

[bobfather]

It could be a collapsing air pipe, it's been happening more and more frequently with these cars. As you open the throttle the air demand can exceed available air filter flow causing a vacuum in the pipework between filter and AFM. The collapse usually occurs low down where the pipe bends into the nose cone. Once collapsed you'll suffer air starvation.

The cause could be dirty air filter, blocked mesh or perished air pipe

[dwhitaker]

I have hooked up roverguage, all seems well.

[ChimpOnGas]

dwhitaker said:

I have a new coil, because the old one had leaked early last year, but not fitted that yet, is it a possible culprit?

Ignition coils produce a lot of heat and the oil inside your coil is there to stop it overheating, if it's leaked as you say it goes without saying you need to fit your new coil immediately.

As engine speed increases you are asking more from your coil because there's a lot less time to charge it to it's maximum energy level, so if the coil is overheating it will most likely present misfires as you accelerate, and it may well simply produce no spark at all above a certain rpm/heat threshold.

If your coil leaked oil it will almost certainly be overheating, so you should change it for the new one as soon as possible.

[Steve_D]

Have you fitted a new air filter?
Did it come with a manufacturer's sticky back label in a poly bag?
Did you forget to remove it from inside the filter?
Is it now jammed in the MAF?

Ask me how I know.

Steve

[bobfather]

Steve_D said:

Have you fitted a new air filter?
Did it come with a manufacturer's sticky back label in a poly bag?
Did you forget to remove it from inside the filter?
Is it now jammed in the MAF?

Ask me how I know.

Steve

^^this^^

The symptoms you describe are classic induction air pipe collapse or other air restriction

Edited by bobfather on Thursday 8th June 08:05

[jimed]

The comment re the induction hose collapsing is very real. Mine didn't collapse but it looked a bit tired so I decided to replace it with the smooth bore induction pipe and when the old "looks tired but fine" pipe was off you should have seen it - what a mess it was underneath (split round the wire winding and in shreds in places) to the extent that it could well have collapsed at any time so a quick look and "it seems ok" may not tell you the truth. I'm not sure but think I was told that the induction hose is double skinned so it is possible that the outside might not look bad but the inside cover could be split and come away in a flap that effectively closes the hose under acceleration because of the higher air flow. This does seem to be the most likely thing but then you never know..... . Good luck in sorting it.
Jim

[Classic Chim]

^^^^^^ this
Change the coil first

[SwanJack]

I had this problem, the fuel pump wiring had deteriorated to the extent that under load the circuit was giving 9V to the pump (not under load 12v was showing). I replaced the wiring, problem went away.

[blitzracing]

Im surprised you have not thrown up a fault code if its an intake restriction - a collapsed induction pipe can throw up a low fuel pressure error, - odd I know- but I think its because the plenum pressure is lower than it should be due to the restrictions and pulls the fuel pressure down accordingly, so the engine runs very lean on both banks. As COG says coil is a major point here, as the HT will drop off as it heats up, but a missing spark wont throw an error code that easily.