H-e-l-p

My car is still miss firing.....the problem started some seven weeks ago when the red top fuel pump packed up, I replaced it with a silver top fuel pump which pumps out 30 gallons an hour compaired with 35 gallons that the red top puts out, the fuel line has a pressure regulator on it before going to an inline filter then off to one bank of 45 doe carbs and out to the other. I have replaced the filter, the fuel line, checked the omex coil pack, replaced the spark plugs and leads and the car runs fine for ten mins until warm and then the miss fire occurs at 1500rpm til 3500 rpm then disappears, I was wondering if anyone has ever come across this, as even an alfa specialist is baffled and hes had the car for a few weeks. At this momment it time any suggestion (other than scrapping it) would be welcome.

is the pressure regulator adjustable? i spent days looking for a miss on a 2.0 105, the idiot i worked for swore blind he didn't touch anything when he was checking the oil level (when the miss started ) funny that when i got a little frustrated, i twiddled the pressure regulator dial, (which when i was an aprentice i was told, "touch and die" by the head mechanic of the time, apparently took him ages to set up) and it ran better, and an hour later, i'd played until it was right, and all was fine.

If the regulator isn't adjustable, was it matched to the higher flow pump? is the pump a leccy one? (guessing it is with the powah you pump out)

I would say that the regulator isn't letting enough fuel through, as it was built for a bigger pressure behind it, just took a long time explaining myself

Good luck!! hope this helps!!

Problem with similar symptons turned out to be loose fuel pipes i.e. I hadnt done clips up properly / square .

Another solution was to blank off the fuel return pipe.

Not all facet pumps have one way valves fitted. When I went from Mitsuba pumps (absolutely brilliant) to facet I had the above problem occur. Problem was intermittent but when it occured the only way to solve it was to block off fuel return. Prefer to run with one so that fuel vapourisation probs dont occur on rally car. Only went to facet because at that time I couldnt find a supplier of Mitsuba.

Speaking to Facet they said it was to do with one way valves helping to maintain pressure. Without it the pump goes at a constant speed and once pressure is achieved the pump just sort of skids? With the Mitsuba pumps even with the return pipe connected you could hear that pressure was being achieved because the pumps speed was fluctuating to maintain line pressure.

Not sure if this is of any help but good luck

rsfruitbat

ta for the info guys, and yes the regulator is adjustable, i have mentioned this to the mender and to his knowledge he says it should not need tweaking.....im begining to wonder. The car has no return pipe as its blocked off on the near side bank of carbs.

If i were you, i'd have a play with it, maybe let the pressure off a bit, so more pressure can flow through to the carbs, since the only thing changed is the pump, and it's flow rate is different, i would have thought it essential to try the regulator.

Using the logic of old cars, when one thing is repaired, something else unrelated breaks at the same time....

Originally Posted by Iain.Oglethorpe

and the car runs fine for ten mins until warm

I think your clue is here. If it was a fuel problem surely you wouldn't be able to drive through it to higher revs where you require more fuel?

Does it have a choke or cold start device which allows it to run OK until it is warmed up?

Is everything earthed OK - coil, fuel pump.

Originally Posted by RicksAlfas

Using the logic of old cars, when one thing is repaired, something else unrelated breaks at the same time....




I think your clue is here. If it was a fuel problem surely you wouldn't be able to drive through it to higher revs where you require more fuel?

Does it have a choke or cold start device which allows it to run OK until it is warmed up?

Is everything earthed OK - coil, fuel pump.

Now there's something...

I had an issue with poor running when warm. Had sima similar miss and eventually, the car wouldnt run and was a nightmare to start again. It turned out that the choke was working itself open on on side when the car ran for 15/20 minutes. I disconnected the cables and its not done it since. Dont know what kind of setup is used on Weber carbs but the dellortos seems to be prone to this problem if the choke cable is worn or damaged.

The choke has been totally binned when the race engine was put in and the carbs are 45s webbers and have been completely rebuilt and still the issue is there. There is no cold start device to alter any of the fuelling and like I mentioned before the car revs to 8500rpm and is fine as long as it above 3500rpm when warm which still makes me think that fuel pressure proberly isn't the issue. I think it may be time to drop the engine and have a look at the heads, might be a sunken valve or a tiny crack in the head. And another note the car was putting out 197bhp and the dyno now reads 173bhp with the miss fire. effing car.

Wow those figures are impressive. Have you been able to narrow down the miss to a specific cylinder.

Just out of interest, how is the box holding up with the power your engine is putting out?

I broke a g/box last october from a 1.7, and I managed to scorce a 1.5 amica box(what my car originally started with) shortly after and it transformed the acceleration , I do try to be a little light footed when in 1st and 2nd though. And no im afraid i don't know which cylinder is giving me gip yet and the car is on the back burner this weekend as the wifes b/day is looming.

first an excuse for my poor english,

what fuelpressure are you running?
maybe your carbs are overfloating because of to much fuelpressure
0.3 - 0.35 bar is enough, any higher and the carbs will overfloat, that could explain why your engine is running fine in higher revs, because the fuel will be used more

when the engine is cold, it will also use more fuel, so that all is used before overfloating the carbs

i hope you know what i mean

Good point Graffiaturo, the car is in the hands of the guy who built the engine so hopfully will have somthing sorted out by next week, fingers crossed.

problem solved?

I thank you all for the advice, the cars issue is now rectified just got to mot it now so will be using the 147 for chatham , perhaps I will meet some of you?.

Originally Posted by Iain.Oglethorpe

I thank you all for the advice, the cars issue is now rectified just got to mot it now so will be using the 147 for chatham , perhaps I will meet some of you?.

Glad to hear its all ok again. What was the cause of the problem?

We think it was a combination of things Fuel pressure, dirty carb and a ht lead, the engine is back on song but might need an hour or two on the dyno .

Good news Ian - hope it wasn't too expensive to sort out though!

No , not that bad just a few hours labour, the funny thing is the car runs better now than it had done before the problem, although I was told the main jets may need to be bigger as throttle response had a tiny delay (hiccup like symptom) from low revs but I can live with that.