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Help with diagnostic? 

 

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 Post subject: Help with diagnostic?
Posted: Sun Aug 19, 2007 2:22 pm 
Oompa Loompa
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Ride: P6/XC Hearse [302]

Location: Sydney
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During a recent road trip (about a four hour run at night), my car kept conking out, and I'd appreciate any insight as to what may be causing this.

It ran fine for the first half of the journey, then would dramatically lose power: pigrooting/lurching and bogging down to a crawl until stalling. I'd wait 10 or so minutes, then it'd start and run fine for another 20km or so, and die again. This happened about a dozen times before I was able to limp to a friend's house.

It's a '77 XC 302C auto with standard carb and power steering.

Some curiosities about the trip:

- It was the first long drive after having sat for a few years.

- Fresh oil and filter, yet the oil pressure light kept coming on (would go out during heavy acceleration, and flicker while lurching). I gave it an extra litre en route just in case, but this changed nothing. A later check when cold showed it to be slightly overfilled with oil.

- Fresh fuel filter (and new lines each end).

- New master cylinder.

- The choke cable is inoperable, and the choke itself is open but flapping around loosely.

- There's a short in the dashboard and parking lights that comes and goes most times it hits a small bump in the road. A headlight globe also blew en-route, but that's all probably unrelated -- ie: all fuses are intact.

Obviously it's in a general state of disrepair, but I need to get it back where I can garage it properly. My first suspicion is the fuel pump, but the behaviour of the oil light is confusing. Sheesh, there's a syndrome of things needing fixing, but I'm trying to pin down the one thing that'll let me get it home safely for now. Can anyone offer suggestions as to what I should be looking for? Pretty please?
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Posted: Sun Aug 19, 2007 3:56 pm 
Getting Side Ways
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Makes me wonder about your oil pump. At low engine speeds such as when its lurching it wont show oil pressure, but at higher revs it will? Get a decent oil pressure on there and have a look asap. also, try and secure the choke with a bit of wire just in case its shutting

 

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Posted: Sun Aug 19, 2007 3:59 pm 
Oompa Loompa
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The weird thing is that it runs fine (for a while) again after the engine's settled.

Also, if the oil pressure is critically low, wouldn't there be signs of overheating?
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Posted: Sun Aug 19, 2007 11:35 pm 
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Has it got a mechanical fuel pump? Sounds like fuel and you probably have a d**k connection to the oil pressure switch. Hasn't got s**t or gummed up fuel in the float bowls?
Otherwise you might want to check you haven't sheared the roll pin in the dizzy gear. Although I would have expected backfiring to be a symptom.

Pete.
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Posted: Mon Aug 20, 2007 6:10 pm 
Getting Side Ways
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Check for play in the dizzy shaft.

Also I gather you have a thermoquad on it? Mine had the same symptoms until i had it rebuilt

Do you hear any change in engine noise when the oil warning light comes on?
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Posted: Tue Aug 21, 2007 5:31 pm 
Oompa Loompa
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Ride: P6/XC Hearse [302]

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Many thanks for your responses.

The carb is indeed a Thermoquad, but at some stage (in its previous life) a choke cable was installed. A rebuild and thorough clean is certainly overdue, but I'm loathe to attempt that scary little job until I get it home.

There's no backfiring, the engine just starts acting like it's strangled and loses momentum. (This is while cruising at freeway speeds.) This is interrupted by jolts of normal power (during which the oil light blinks off), so the car just kangaroos until it runs out of steam altogether. 10-15 minutes later, it's good to go again -- which makes me wonder about cool-down or flooding?

I'll check the distributor anyway, but I'm mostly inclined to suspect a fuel delivery problem (although the oil pressure light raises questions too). I do wonder about the (mechanical) fuel pump, but have no idea how to test/verify this?

Last edited by Heretic on Tue Aug 21, 2007 6:35 pm, edited 1 time in total.

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 Post subject: ??
Posted: Tue Aug 21, 2007 6:02 pm 
Getting Side Ways
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First guess. Crap in the carby, second possible diaphragm if a mechanical fuel pump. Definitly sounds like fuel. Could also be fuel filter has picked up crap in tank after standing or old fuel has gone to jelly and is blocking things.

 

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Posted: Tue Aug 21, 2007 10:31 pm 
Oompa Loompa
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The fuel filter has me thinking. Although I replaced it before the trip, you have a point: it's no reason to believe it's not blocked up with crap. (Hmm, I really should've checked that.)

[fingers crossed]
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Posted: Wed Aug 22, 2007 9:42 am 
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Check the sock on the fuel pickup also.
I have seen a magna do this and also a forklift and it was this both times.
With the forklift we just stuck a air line down the hose and reverse flushed it.

 

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Posted: Wed Aug 22, 2007 10:15 am 
Getting Side Ways
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Har har you've come across the dreaded ford XA to XC problem.

Try a new and approved ford petrol cap, the petrol cap has to be of a good quality too not a cheap s**t one, also make sure the overflow pipe in the tank is not blocked.
Fords from that era had troubles with the fuel system not breathing correctly due to people using s**t after market parts, this caused a vaccum in the fuel tank, which starved the engine of fuel.
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Posted: Wed Aug 22, 2007 7:20 pm 
Oompa Loompa
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Ride: P6/XC Hearse [302]

Location: Sydney
NSW, Australia

I replaced the fuel cap (with a locking one) when I first bought the car 10 years ago. It's definitely not the problem I'm having now, but thanks for chipping in.

Could be the fuel sock too, which makes sense considering the car had been sitting for a few years. The tank is probably full of rust flakes, water blobs and crap, which get shaken up whenever the car is moving. (Flushing the tank is something I'll have to do later.)

The car's a long way from home, so if a replacement fuel filter doesn't clear it up, I'll try a dodgy airblast at a servo along the way. I'm making the trip in the next day or two, wish me luck!

These tips have been very helpful, so thanks again.
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Posted: Sat Aug 25, 2007 5:29 pm 
Getting Side Ways
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Sounds like the coil.
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