Technical UNO 1.1 97 model runs fine until just over 100kmH

[Thallium]

Hi All...

i have been searching this forum for about the last 4 hours and have gone blue in the face :bang: , i am battling to find help for my girlfriends UNO. it's an uno mia 1.1ltr 97 model, it has a carb.

Okay, this is what happens, the car drives quite well, but it does have erratic idling, you can drive it hard in 1st, 2nd and 3rd gear and it runs perfect, but as soon as you reach just around 100kmh, it will start shuddering like its lacking fuel or something, but if you slack off, it works fine again. irrelevant if you are in 4th gear or 5th gear, the carb has just recently been serviced too

i have replaced the dizzy cap and rotor, also put new plugs, air filter and fuel filter. brand new leads as well...

the diaphragm on the dizzy seams okay, the pipe to the diaphragm is still good, but the dizzy amplifier module or ignition module has been replaced aswell because the previous one would over heat and the car would have to stand for up to half an hour, but the new one gets very hot as well, it has been moved and mounted by the one shock with a large peice of metal to try and cool it down

ok here is the breakdown

1. shudders over 100kmH
2. new plugs, filters, leads, dizzy cap, rotor
3. diaphragm good
4. VERY hot dizzy ignition module
5. Carb been Serviced
6. Cant find any air leaks

All help will be greatly appreciated :worship:

P.S. Great forum

EDIT: Sorry, its the 999cc engine, not 1116cc

 

[alexGS]

Hi Thallium,
and welcome to the forum

My first suspect would be the fuel pump. What often happens is that the pushrod (that operates the pump off the camshaft) wears down. You can adjust this to some extent by using thinner gaskets on the hard plastic spacer (puts the pump closer to the operating cam). I'd suggest removing the gaskets completely and going for a drive to see if there's any change. Or, you could just get hold of a second-hand spare.

As for the really-hot distributor module, have you tried changing the coil? Maybe it has a short in the windings and presents a high load to the module. Again a second-hand coil should be sufficient as they don't fail often. Or before going to the trouble, you could measure the resistance. Haynes quotes two sets of resistances:
Coil BA506A: primary 0.756 - 0.924 Ohm
secondary 3330 - 4070 Ohm

Coil BA506D: primary 0.666 - 0.814 Ohm
secondary 2970 - 3630 Ohm

Another item to check is the air gap of the pickup in the distributor. With the distributor removed, it should be possible to just feel 'bumps' as the four-lobed rotor goes past the magnetic pickup. Also the wires to the pickup frequently lose their insulation. You can re-insulate them with fibreglass 'spaghetti' tubing of the type used in ovens (and sold by electronic shops). Come to think of it, frayed/shorting wires might explain the hot module and the idling rather well

After doing both of the above, further troubleshooting of the shuddering could be accomplished by driving up to 100km/h so it starts playing up for a while, then engage neutral, switch the engine off, and coast to a halt (obviously, do this somewhere where the manoeuvre can be performed safely and bear in mind that the servo brake will only operate a couple of times with the engine off, after that you'll have to press much harder on the pedal). Disclaimer: no responsibility accepted for damage or injury from following this advice... Anyway, you could then remove the top from the carburettor (with the air cleaner off, it's only four screws if I remember correctly) and see if it's full of petrol or not.

Hope that gives you a few more things to try?

Cheers,
-Alex

 

[Thallium]

Alex, thanks for the great advice...

i was expecting you to reply first, i see that your very helpfull around this forum. thanks.

Oh, i forgot to mention, when the car, no matter if its cold, hot, if its been running for 3 hours or 1 minute, it cannot go over around 110kmh in 5th, my girlfriend just told me its battling to go over 80 or so in 4th, that only started when i changed the leads, plugs, dizzy cap etc etc. but she went to 5th and it was fine until around 100. does this change your opinion?

i'm thinking more in the lines of a bad fuel pump and bad pickup signal to the distro module.

a lot of mechanics has fiddled with this car trying to fix it, when i got my hands in there, a spark plug in the second chamber would only screw in halfway, thats how bad it was stripped, so i'm suspecting the car has been tuned with that bad plug and the air/fuel mixture has been fiddled with. :bang:

i think the first thing i'm going to do is check or change the wiring from the pickup, check the pickup as well, and test the coil, and check that fuel pump.

what do you think Alex?

Thanks once again. :worship:

 

[(CZ)enda]

Did you have the advance timing set up/serviced?

 

[Thallium]

Hi (CZ)enda.. thanks for the reply

but no, i haven't done anything yet, but i'm not sure if it has been done before by the previous mechanic, i see some fresh markings on the rotor housing, but i don't know if anybody has done any timing at all or they just did that to get it back to where it was when they extended the pickup wires to the dizzy module...

there is a very long wire from the pickup to the dizzy module, over a metre, do you think that will weaken the already weak signal from the pickup?

i'm going to find and fix all the dodgy stuff first, then get onto the timing and mixture..

thanks for the help guys :worship:

 

[alexGS]

Hmmm - thanks for the kind comments. I've been a bit slack round here lately, busy with fixing cars (funnily enough...)

I don't think my opinion changes though - still the same things, although (CZ)enda has a point, the timing could be out. Check the cam timing as well, in case the belt's been changed without due care - one tooth off might cause the loss of performance you describe. There is a notch in the cylinder head at about '48 minutes' (imagining the cam pulley to be a clock face!) There is a fine line on the cam pulley that should align with this notch - with the crankshaft set to TDC (ridge on plastic belt cover aligned with notch in crank pulley, or flywheel round dint lined up with leftmost line on gearbox bellhousing window...)

Sorry that's a lot of info written quickly - hope it's sufficient to help you check the timing, a fairly quick job as the cover is easy to remove and you can turn the engine pretty accurately by pushing the car forward with 4th or 5th gear engaged

The ignition timing, meanwhile, should be 5 degrees BTDC (middle line in bellhousing window) with the engine turning at idle speed (less than 900RPM) and the vacuum advance disconnected & blocked.

As for the relocation of the amplifier module; I would tend to relocate it back onto the distributor, as there's a risk of the long pickup wires picking up interference from the plug leads. So I agree with your plan! I'm sure you'll get it running better - top speed should be about 140km/h with everything set up right.

-Alex

 

[Thallium]

As for the relocation of the amplifier module; I would tend to relocate it back onto the distributor, as there's a risk of the long pickup wires picking up interference from the plug leads. So I agree with your plan! I'm sure you'll get it running better - top speed should be about 140km/h with everything set up right.

-Alex

Thanks Alex, you just sparked a neuron in my brain

the amplifier module is mounted near the right shock looking from the front, that new cable that a previous mechanic put in from the pickup to the amplifier hangs loose, its also rolled up about 3 turns in the middle just hanging, why do i have this feeling that when you reach roughly 100kmh the wind pushing through the engine bay is pushing that cable near the plug leads.. the jerking is a little worse since i changed the leads.. :chin:

new leads, better spark traveling through, slightly worse jerking around 100, cable pushed by wind close to new leads.. mmmmmmmmmm.

if a signal gets "noise" before it is amplified, the noise will be amplified in the same way as the signal.

thanks a ton for the help Alex, i can only work on the car this weekend, but i will let you know what i did and if its fixed..

 

[premrajeev]

nice advise alex!

I'm also trying these as i was also facing some kinda jerks for a long time..

Will et u know the outcome soon..

 

[Thallium]

Hi Guys

thanks a million for your help, i managed to fix the problem...

This is what i did.

first i re-wired the amplifier module and tested the coil, all was good, but it improved the problem only slightly. seems to have given me a little bit of ignition performance and better idling

second i replaced the fuel pump with a brand new one, that made no difference, so i guess the old one was still fine...

third, i set and adjusted the rotor housing clockwise to advance it slighty, after a few test drives and adjustments, i managed to get the car to reach about 120kph. and uphill suffered around 100kph so that improved timing a little. but that told me that it's definitely a fuel problem

fourth, i sanded down the spacer for the fuel pump probably just under a mm, and set the float level in the carb because i saw someone had fiddled with it and was slightly bent where the float holds the insert needle. i had to sand the spacer, the old gaskets were so old, they became part of the spacer, haha.

i also redid the timing a little after i got a decent fuel supply and decent ignition.

and voila, the car can go full throttle up any hill without a single splutter.

and can now reach about 150kph easily

petrol usage is better, and the temperature goes max to just under halfway, and only goes about just under a third on the highway

so i think that car is good enough for now until i can get the timing set properly and the mixture adjusted properly. i had to do it by ear... and i saw that someone else had already fiddled with the mixture, and its probably wrong because of all the other problems the car had... but the timing is damn close to perfect right now

but, thanks a million guys and Alex, you helped me sort my problem out.. :worship:

 

[alexGS]

...but, thanks a million guys and Alex, you helped me sort my problem out.. :worship:

Ha, no... you helped yourself out
That's ingenuity, sanding down the spacer. And notice how a persistent approach across a number of areas is what gets you the result many people give up when it's not fixed by the first thing they try.

Isn't it satisfying to get the final result, though... makes it worth it and think of the money you saved...

I don't know if you can still buy timing lights where you are - they're nearly obsolete (cars like the Tipo and my Uno Turbo do not have readily-adjustable timing, and those cars are nearly at the end of their lives...)

Anyway I bought a very good timing light - simple, effective - only a year or two ago. The brand is Optilux (German). I think it is well worth the money in being able to check many different engines (even the ones where you can't adjust the timing, at least you can tell if something is wrong...)

Setting the mixture by ear - yes, I've done that too - good luck It's quite a case of trial-and-error. I've found, with the Uno, that the mixture screw frequently has little or no effect. A FIAT specialist suggested enlarging the idle jet, which I tried, and it worked brilliantly (the mixture screw then made a real difference because there was more fuel available).

The theory is that the throttle spindle etc. wears over time, letting in extra air, and by enlarging the idle jet you have some extra fuel available to balance this out. The standard jet tends to be '45' (0.45mm) and can be safely enlarged to 0.50 or 0.60. I tried a 0.70 in there and that started to have detrimental effects when driving off (progression to main jet not correct), so I then bought some tiny drill bits (0.5, 0.55, and 0.60) and now I can make this modification to any Uno that I feel needs it - I've done it twice A bit naughty as of course the jet marking would be wrong, so I try to amend it. Incidentally these drills are REALLY small so I grip them in a 'pin vice' shaped like a jeweller's screwdriver.

The surprising thing is that in both cases, enlarging the jet had an immediate effect on the engine - smooth idle, with no adjustment being necessary! In one case I had to increase the fast-idle on the choke, because the choke was so much more effective (with the additional fuel available) that the engine could not idle when cold if the choke was pulled out too far! Increasing the fast idle reduced the amount the choke had to be pulled out and solved the problem.

Anyway, well done and good luck with any future tweaks.
-Alex