Loss of power/backfire after engine gets hot

Not at all uncommon for a coil to be heat sensitive, it's fine until it gets hot then it dies. Just incase you were running out of possible causes.

Lester

 

The coils seemed fine last time we investigated this but it is another item to consider.

The plug leads were fixed into standard clips in the standard position for a 328.

GG

 

Have you checked the Fuel Accumulator? It is located near the Fuel Pump and is there to maintain a constant fuel pressure. Sometimes they have a faulty pre-load spring and that lets the Fuel Pressure drop off. Also is they are faulty, sometimes there is a small amount of fuel seepage, which may account for the fuel smell.

 

have you ever tried to install / borrow an alternative microplex ecu ?

if not, do give it a try (I know they are hard to get and very expensive ...)
but maybe some fellow F-chatter near you will chime in

 

I have not checked the fuel accumulator, so that is another item to add to the list. However the fuel smell has now gone. It was traced to a small leak in the fuel return pipe (so far as I remember) and that has now been replaced.

I have not tried an alternative multiplex ECU either. I would be a great idea, but given the intermittent nature of this fault, I might need to borrow one for an extended period. I am not sure how practical that would be.

GG

 

Most importantly, remember the old adage;

90% of ignition problems are fuel and 90% of fuel problems are ignition.

Lester

 

My 1980 308 "i" does the same thing once warm. I'd love to get two hours before it kicked in.

 

That sounds like a useful adage, except that I don't know whether it is fuel or ignition!

Yes, climb, it is enormously frustrating. I am luckier than you in that I can go for long drives with no problem most of the time.

GG

 

I am wondering if the heat in the engine bay is heating up the fuel supply pipes to the injection system and its return line to the tank.
You mentioned that it takes 2 hours for the fault to appear- assuming you have a full fuel tank and you start your journey, the fuel pump will supply enough fuel for the engine on max power/ speed so on the road most of the fuel is being returned via pressure setting valve to the fuel tank.

In the morning the fuel in the tank is at the outside air temperature, as the engine is running most of the fuel is returned to the tank, picking up heat from the engine compartment. If you are running at higher speed the heat in the engine bay increases and the fuel lines pick up more heat which goes back to the tank, increasing the temp of the fuel in the tank.

The level of fuel in the tank is getting lower so less fuel to absorb the heat and it gets hotter. We must get to a point that the fuel temperature is hot enough to upset the fuel injection system.

It might be an idea to look at the main fuel supply and return lines- are they original or have the run of the pipes been moved. You can get insulation to cover these pipes to ensure they do not pick up heat.

When the car starts up feel the temperature of the top of the fuel distributor ( housing on rear left hand side with all the small banjo pipes coming out ), then feel the temperature after a long run. Should not be much difference.

 

That is happening for sure because the OP mentioned the heat in the bulkhead area is so high that its burning the ignition leads.

If the heat is enough to burn the leads it will surely cause issues with the fuel pipe even if its not been re-routed. So hence the misfire as all of the fuel heats up.

The question is why is there excessive heat and the prime suspect for this has to be either an exhaust leak or an ignition problem causing timing to be out.

Which is why the first thing to check is the timing curve is correct. It might be the case that is wrong even from cold, and the symptoms only appear once everything has overheated.

I dont believe the addition of the heat shielding material on its own, which the car has, would cause this unless its spaced much closer to the engine than the bulkhead normally would be. But it would certainly do no harm to put the fuel transfer pipe behind the sheet if the timing is first confirmed to be OK.

Edit:
Just thinking some more, is the added insulation material over the top of the factory foam layer? If so, this will indeed considerably narrow the air gap. Or was the foam removed before it was installed?

 

Just had another look at the picture on page 3.

Unless the picture is misleading owing to the angle, this appears to show the reflective material is one piece which runs all the way from the top of the bulkhead downwards.

If this is actually the case, this would almost certainly be the issue.

It should be in two pieces, the top section which is above where the fuel pipe runs, which is on the back of the parcel shelf, and the lower section which is about an inch further forward. The fuel pipes should run along the top of this further-forward section.

If the pipe is running level with the top section its an inch closer to the exhaust than it should be.

 

Bit hard for me to say as i had the mondial, which i dont have anymore. A set of pics from a similar car would be a great help here if someone can help.

The interesting point is the problem takes a couple of hours to develop so hence my point about build up of heat in the circulating fuel. Timing must be ok as its running fine for 2 hours.

A standard OBD scanner should be able to check the ignition timing, it will on my 430 so hopefully you will be lucky

 

Here are a couple more photographs of the engine bay -- one not particularly good - showing the position of the added aluminium heat shield. (Ignore the mix of black and red ignition leads etc, the black ones were made as a temporary measure to allow the car to run on eight cylinders after burning two leads.) There are two layers of this material, back to back, and they have been placed over the top of the original foam.

The material is not in one piece, or at least there is a step. However by placing it on top of the foam, the space between heat shield and some of the fuel system components is now quite small.

The idea about the fuel and fuel tank heating up would certainly fit with most of the symptoms. I will try the distributor heat test after the next decent run.

GG
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That setup could be the problem. The gap is supposed to be far wider.
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Is that the fuel line sitting in the gap between the insulation panels ? It must be hard up against the bulkhead then.

 

The upper pipe is the breather, the one that seems to tuck underneath it is the pipe from the fuel filter to the fuel metering system.

GG

 

Andyww pic seems to show the fuel pipe from the filter sitting on top of the lower insulation pad

 

Is that the fuel pipe in Andy's picture, or the breather between the two tanks? The one above looks like the black venting tube that has been mentioned in the other thread. I don't have that (I don't yet know if it is missing of the layout of the Euro car is different)

GG

 

Can you send a picture of your previous two burned wires? I beileve if it was heat from the engine, then all four wires would be burnt by too much heat. You mentioned that the wires were actually on fire which leads me to believe you have an internal electrical/ignition problem. Perhaps these wires are shorting out somewhere between the distributor cap or extenders. I would highly recommend eliminating the extenders completely as I did a few years ago and I can show you how,

Joe

 

What if you mounted a cooling fan or two somewhere in the engine bay of hood to move the air. Dunno If you'd try to pull the hot air out or if you'd wanna push fresh air in to the area. Wouldn't solve the source of heat problem but at least if it helped or eliminated the condition it'd let ya know it's vapor lock or overheated fuel.

 

All the extra insulation is stopping a lot of the normal airflow, so if that goes it will be like it was when built

 

jlc308, the cables are long gone, I am afraid. However I do not think it is an electrical fault that is causing the burnt leads. Most likely the one that was in flames -- the cable to the right front cylinder and therefore the longest lead -- got hot and eventually dropped out of its mounting clip, falling onto the manifold which is just below. That would soon lead to the fire, I suspect. The next cable along was still in its clip but was slightly charred where it ran though the clip. This could be from the burning lead or simply from heat rising from the manifold.

mike32, yes that is what I am hoping.

GG

 

I think we've figured it out (on mine). On a hunch we popped off the distributor caps, see if you can spot the problem.

Left rotor:



Right rotor:



Ordered a replacement distributor cap and rotor, and going to see if that makes it go back to being normal

 

Congratulations on finding the cause of your issue, fluffypony. A broken wire in a distributor was one idea I'd suggested to the op. At first glance I thought this was the op that found their problem. Good news, anyway.

 

See! You didn't really need all that stuff for the car to run didya. ;-) It's amazing to see how far out of whack things can get and the car will still run reasonably well.