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Engine running rough...


franksm

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Hey folks

I ran the car low on fuel last night, red light was on quite a whiles. Filled it up, then after 15 miles or so it starting misfiring under load - no popping or backfiring, but just "missing". Idles fine. All the electrical stuff is tight and dry (coil, plugs, etc). I always imagined such "missing" would be an electrical problem, while noisy misfiring would be a fuel problem (because of a lean condition in the mixture). Is that theory wrong ?

The engine-bay fuel filter gets "full" during priming before the engine is started, but looks rather dry of fuel while the engine is running. Is that normal ? I never noticed before. Doesn't sound right, and I would have imagined seeing fuel bubbling away in there at all times.

The fuel pump is ticking once every 5 seconds or so (except during priming when it ticks fast for about 3 seconds. Does that sound normal ? Again, I have never noticed, so can't say.

Gut feeling is that I have blocked the fuel pump with some gunk from the tank, or else the pump has just decided enough is enough. Any ideas welcome !

Frank

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I went ahead and looked at the filter near the carbs - it looked okay until I shook it up a little - it's full of rusty powder.

However, blowing down the pipe between the pump and filter needs more effort than I think is good - I'll have to see if there's a blockage there.

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Ah well... think I'm sorted - fuel filter was silted up with rusty powder: replaced that,

Blew through all the pipes (don't ask) and made sure they were clear.

Took the fuel-pump to pieces and cleaned it up.

Now getting a nice, full filter. Car runs okay - will do a proper test drive later.

Interestingly the pipes weren't easy to blow through (like blowing up a balloon) - maybe 'cos there;s 12 feet of pipe in there, that's to be expected.

Just need to neutralise the taste of petrol in my mouth, now. Is it too early for a vindaloo ?

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  • 4 weeks later...

I feel like I'm in Groundhog Day! Exactly the same thing just started with mine. Ran fuel low and developed a miss. Should point out have just finished a resto job and car has been off the road 7 years. Miss developed after turning a corner. I had a previous problem with sticking needle and seat in right hand carbie after removing to do manifold gasket. Found red gunk in both float chambers. Cleaned out carbies removed fuel tank and flushed and replaced filter which was filled with same red oxide gunk. Thought nothing more of it till I went out for a Sunday run and 12km in it started to miss (run on 4cylinders ) again. Car will run for 10-20km then as soon as I turn a corner its starts to miss again. Removed carbies again and put 'carbie clean through both. Replaced condenser as this is a known Stag problem which can induce a miss after driving. Put a petrol tratment through the petrol and filled tank. Guess what? Its still doing it. Have fitted a fuel pressure gauge to the line. Holding 2.5-3.5psi. I have had this going on now for 6 weeks. I have soldered every wire connection in the high and low tension circuit and cant sort it. The only clue I have gleaned is that if I turn a left hand corner and it starts to miss the left hand exhast pipe blows a blue/white smoke and the pipe goes a light grey inside. It happened when I turned a right hand corner the right hand pipe went light grey/white inside. I have felt it was fuel related from the outset almost like a vapour lock. The car has no power and its not just a miss. Its only running on 4 cylinders. Its almost like one whole bank shuts down! I limp the car home on 4cylinders turn it off and let it sit for 5 mins then restart it and the problem goes away till I drive for another 10km then its back. It seems totally intermittant. I drive to the local shops and back no problem. Then I do a reverse turn in the driveway and I cant get it back in the garage! I am at a total loss! The Stag guys I deal with here in Oz reckon that the first step is to replace my single point dizzy with a Bosch/Ford electronic one and a 'super dooper' coil. ($575AUD). You can imagine I am reluctant to spend those sorts of bucks on a Sunday driver. I bought it as a wreck for $3500 and have restored it myself. My question is? Do you have electronic ignition in your car? If you do then I know mine is not Dizzy related and I can look at further fuel/carbie solutions. Thanks Mick

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I should have noted that I had all the same symptoms and tried all the same fixes as you did. When I checked with the Stag gurus they told me that the fuel filter will fill on start up then appear empty during running. The only way to test was to remove fuel lines at the carbies to make sure they have good flow and fit a low pressure (fuel) gauge to the line and run it into the cabin to check if it was a lack of pressure causing the problem. It wasnt!


[sub]2x 1977 Stags
1x 1972 MG Midget
1x 1969 GT Falcon[/sub]

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franksm wrote:
Blew through all the pipes (don't ask) and made sure they were clear.

Interestingly the pipes weren't easy to blow through (like blowing up a balloon) - maybe 'cos there;s 12 feet of pipe in there, that's to be expected.

Just need to neutralise the taste of petrol in my mouth, now. Is it too early for a vindaloo ?


lol. I bet that was an enjoyable experience! I would imagine they'll be mildly difficult to blow through as they are long with not much bore. I wonder if you could adapt a bike pump or something to connect to the pipe?

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heh heh I am well used to the taste of petrol. It's 10x better than the taste of gearbox oil (ugh... once tasted, never forgotten).

Since I started having these running problems, I changed the fuel filter, fuel pump (nice and strong albeit noisier now), and blew the lines. I also fitted a new alternator as the old one was noisy.

All was fine for a while. Until, with the cold/wet weather I noticed... when I had the headlamps on, the wipers would slow down... Plus the blinkers weren't blinking properly. Sure sign of electrical problems. Plus with lights on, the engine would falter at idle. So, it must be my battery. It's getting a healthy 14v when running, yet sits at 11v at night.

Hopefully that's my problem.

Lesson learned: if your blinkers are slow, or not blinking, they're not getting enough from the battery/alternator. Obvious in hindsight

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Hi. My Stag blinkers have always been slow but everything else is OK. I have checked Volts every where else and with lights on and its all good. Got 14V at the fuel pump. Pays to check the inertia cut out switch as well as they can rust up and corode and you wont get a good 12V to the pump. Have done all this but the problem persists.

I have ball valve seats coming for the float chambers and the Gurus tell me that there is a ball valve vent on the side of the carbie which allows the float chambers to breath. This can become stuck and can cause an apparent vapour lock situation.

Mick M
Melbourne

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If you are thinking about changing the ignition set up consider the Pertronix Igniter, brand name in the UK is Aldon.

It fits under the Distributor cap on the plate, no changes, completey replaces points and condenser, uses existing coil.  Its discrete only a red and a black wire, no box under the bonnet.

You can also get an uprated coil, a Flamethrower.

I got both from the Little British Car Company in the US for US$126, if you go on the web site and ask the owner, Jeff Zorn, I am sure he will tell what is the right one for your dissie.  Don't buy from the UK they are twice the price.

He and his wife actually drove a Stag at a recent meet in the States and are thinking about buying one to go with their MGB.

I neither own nor have shares nor am I paid commission by any of these firms just in case any one wants to know.

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Thanks Barry.
I have been toying with a set up recommended here in OZ. Uses a Ford Bosch dizzy and is set up by a mob called performance ignitions in Melbourne. Cost is 575AUD so I am hesitant to spend the bucks if its not an ignition problem. I am going to go over the carbies again on the weekend and hopefully this will sort it. Having done all that I will then look at the ignitor as it sounds like a good simple set up. (and the Aussie dollar just crept over .93 US so I wont cop it in the neck on the exchange rate)
Cheers
Mick

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Mickmtcb wrote:
Thanks for the info. People here keep telling me that I have to get the dizzy 'recurved' to accept EI. Do you have any opinions on this or can shed some light would be helpful.
Kind regards
Mick


No, unless you're some sort of performance freak, just install it and forget about it.

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  • 2 months later...

Hey - you know what this turned out to be (engine dying, stalling, etc) - bad battery.

It was holding a charge, but not enough. When it was really on its last legs, switching on the headlamps would make the engine falter. I thought it was the alternator, but nope, turned out to be that wanted a new battery.

I had been suffering non-blinking indicators for a while too - so that's the sure sign.

Kinda embarrassing after fitting new fuel pump, sparkplugs, dizzy cap, rotor, leads, alternator, belts... :-O

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Yes I managed to sort mine as well but only after fitting the ball valves. When I pulled the old needle and seat out of the right hand Carbie there was a big lump of black rubber that was caught in the seat recess. It appears to have come from the O rings that seal the hot start mechanisms into the carbie where the float chamber vents. Replaced these O rings and have done approx 500kms of uninteruppted weekend cruising in the old girl.

Mick M
Melbourne Oz

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