89 Range Rover backfire in MAF and Vapor Locking behavior in Arizona Summer Stop go t

[magmacu]

I am up to my wits end with the old girl. She is my daily driver (yes I feed it 80 dollars of premium fuel every 2.5 days) for a 90 mile around trip 5 days a week.
I am having this same recurring issue the last two summers here in Arizona, when the temperature climbs above 90 degrees and it is worse when the temp gets above 100+. In stop and go traffic after coming off the freeway, the Rover will backfire (popping into the MAF) from a stop light and it will exhibit vapor locking behavior, and lack power. Eventually, it will some what smooth out once I get moving again. I have found that it is worse if I run into the bank or store for 5 to 10 minutes and try to restart. (If I go shopping for an hour and come back it fires up and runs fine). It is will barely idle, and it vapor locks, and has no power; I have to feather the throttle to keep it running; if I start to get on the coals at the same time it will barely get out of its own way, and it is popping into the MAF of the engine. I have also observed that in the driveway after my trip from the Mine, I rev it will cut out over 2500+ RPM and pop as well. I know this not good for the MAF.
I have replaced the AMP on the distributor, coolant temp sensor, fuel pump, coil, and plug wires. The fan clutch is good, and electric fan runs when the AC is turned on. I have also observed that when the fuel level is more than half a tank it is not as bad as well.
I have poured over the web, and I am sure it is caused by a concentrating of heat under the bonnet, and everything underneath just roasts. The fuel line runs next right exhaust manifold, but it has insulation wrap over it. People have suggested a clothspin, but I am sure that will not do it.
Any guidance would be greatly welcomed.
Bjorn

[MysteryTheatre]

for the backfiring i would look at two things , first check the timing, if you have a timing light set it to six degrees before top dead center with the vacuum hose unhooked and plugged. secondly i'd look at the flame trap and pcv valve and all associated hoses, disconnect everything clean and inspect, possibly replace pcv valve but clean the flame trap by soaking it in gas or spirits and rinsing it out good. As for the vapor lock , for the time being if it occurs just lift the gas cap and that will depressurize the system and should solve the problem temporarily. the real cause is probably a stuck purge valve on the evaporative canister. should be able to get one from british pacific. if you need to in an emercency you can drive it with the gas cap on loosely, but i only advise this in an emergency as the fumes are dangerous.

[lwbblue]

Bjorn; I know of your problem. I experience it also in my 95lwb, only mine is not heat related but occurs after I have gone through the car wash, and only if the guy sprays down the grill/front. I have pulled the disty cap for moisture and checked all plug and other connections. I drove through a massive rain storm; through standing water and at highway speeds last week and no trouble. The problem only goes away after sitting along while, overnight works. To make matters worse, a friend with a 95lwb has the same problems after car washes, and so does another BB guy in Florida.

I believe it is electrical and is related to cutting off ignition momentarily at low rpm. Once you get the revs up it will run fine, until the next light. Very similar to driving a car with very advanced timing, or a plug fowling Porsche. Vacuum leak could be part of it.

A lot of words here and no answer, but after vacuum check, I would be looking at a sensor that gets flaky.

geneo

[bartell]

Originally Posted by magmacu

Any guidance would be greatly welcomed.
Bjorn

Hi Bjørn,

Can you tell me which fueling system you have? If I recall correctly (and I don't always), the US moved to Hotwire type systems long before most everywhere else. Do you have a 13CU or 14CU setup?

James

[TerryS]

Backfiring thru the intake is often an indication of a worn cam. Exhaust lobes get worn to the point that all exhaust gasses are not purged.
The vapor locking can be many things, but as someone mentioned, your purge valve, atop the charcoal cannistor may not be working.

[Elemental]

What spark plugs are you using?