Loss of power/backfire after engine gets hot

In my case I have changed the ignition leads and plugs but the plug extenders have not been changed yet. I am still monitoring the situation. The problem has recurred once, to a lesser degree than previously, after changing the leads and I am hoping that a little more running might clear it -- you never know. If not then I will get the plug extenders changes. As you say Andyww, it is not clear where to go after that.

BlueMax, our problems appear very similar. Mine recovers after cooling down too.

GG

 

What about a smell of petrol in the RHS air intake, BlueMax? Do you get that too?

GG

 

Thanks conan, I'll check that.

I haven't consistently checked the RHS air intake so I do not know if it is only when the car has backfired but there are instances when I can't smell it. I will check this every outing in the future.

There is a history to the petrol smell from the car. When I bought the car in April there was the occasional smell of petrol on the driver's side when driving. I took it to a local specialist who took the car out, detected it too and checked the fuel lines but could find no leak or obvious source. At this time, probably unrelated, the car sometimes idled unevenly, running up to 2000 rpm. The uneven idling cleared itself within a month and I had the cam belts changed. We also changed the filler cap seal. There was also a problem with coolant loss -- it appears the cap was not on properly. That was flushed out and replaced too. Since then -- though these issues may not be related -- the smell of petrol when driving has become much less evident, to the extent that now I sometimes 'think' I smell something but am never quite certain.

While the smell of petrol was stongly evident, the garage smelled very strongly of petrol once or twice, probably after the car had been backfiring and losing power. It was because of this that I started trying to locate the source and found a strong smell in the RHS air intake. A smell in the garage is rare now, though occasionally just about noticeable.

I'm not sure what all this means.

GG

 

I'm trying to find out why, but it is not proving easy. is your air leak source likely to apply to my car which only produces the backfire -- loss of power symptoms under very specific conditions, probably due to some sort of heat build up?

GG

 

The fuel smell in RHS air intake appears to be the same reported by conan, the return line from the fuel injection. I have had that changed and the smell has gone. Thanks for the tip.

GG

 

I had a recurrence of the original problem posted in this thread, the engine getting hot and then a loss of power. Again I found front plug leads had popped out of their holders and two had burned, one rather spectacularly with a small engine fire. This was accompanied by a leaking oil radiator though I cannot imagine that the two are connected. Having replaced the plug leads, my garage then found that only one bank was firing and has traced it to a faulty ignition module. It appears that at some earlier stage an equivalent to a BKL3C was fitted to the car rather than the correct BKL3B or equivalent and this has now failed. Having carried out a quick search about the symptoms of faulty ignition modules, I am wondering if the original problem, loss of power when the engine gets hot, could actually be down to this ignition module getting hot and not performing correctly. While the burnt plug leads are clearly an issue, the car appeared to run reasonably well with burnt plug leads when it was cold. My thesis is that the burnt leads caused some missing, leading to the engine running hotter than it normally would and this was enough to set off the ignition module. I won't know until it never happens again but does this sound plausible to those on the list would have experience with these engines? (I have never been quite convinced that the plug leads themselves would cause the behaviour only when hot, though there may be a mechanism to explain this.)

GG

 

Thanks, and for the list. I have bought another BKL3B from Superformance but I think I'll take your advice and keep a spare from the list.

GG

 

This problem has resurfaced once more. Having replaced burnt plug leads, a dead ignition module that was the wrong model anyway, the oil radiator, put in a set of better spec plugs and oil and tracked down and fixed a small fuel line leak, I thought perhaps the backfiring, loss of power problem was also history, until a couple of days ago. The symptoms were the same as always. After a long drive -- in this case a couple of hours of lively running around some country roads -- I eventually got caught in slow moving traffic and the backfiring on deceleration started with a small but noticeable loss of power. back in the garage there was a distinct smell of petrol in the exhaust.

The only cause I can think of is an unusual heat build up somewhere in the engine after a long drive but then why would that cause ignition problems? Two possible causes that have been suggested previously are either an exhaust manifold gasket leaking when the car is hot or a problem with the warm up regulator. I have not been able to link the issue to either of these so far, so any suggestions would be welcome.

One factor that I have not considered previously but which might have some bearing is that a former owner has replaced the degraded foam that lined the bulkhead between the engine compartment and the passenger compartment with a silver material that looks like a heat shield (see attachment). Could this lead to heat buildup in the forward engine compartment and if so, could that result in ignition problems? Is it plausible for plug leads or the ignition modules which, are in the same area, to start misbehaving if they get too hot?

GG
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So far as I know he plug extenders were not changed with the plug leads so that is worth checking. Also the other ignition module. There has never (so far, fingers crossed) been a problem with starting.

Any ideas about whether the silver heat shield material in the car is likely to create any problems?

GG

 

Thanks, Crowndog, for the suggestion about the vacuum lines and the injector bushings. This is a particularly elusive problem so any ideas are welcome.

andyww, regarding the foam on the bulkhead, do you know its purpose? I had imagined it was sound insulation. Do you suppose that is correct?

GG