Technical Help needed with ignition problems

[awright58]

Hello Everyone

I do not own a Fiat Uno although i think they are excellent cars i wonder if anyone can help me

My father has a UNO 1.1ie it has an 1108 cc fuel injected engine, it is an italian import and it is very sick. My dad says that he has to drive it with the minimum amount of throttle as if he revs it it just cuts out and then every now and then it cuts out and i think he mentioned backfiring. Anyway he took it to a few people one place thought it could be to do with that lambda box that controls the fuel going in and another recons it is the return valve on the barell apparently there is a return bit on the fuel system that regulates fuel preassure in the system i am told that the fuel system should be at 1 bar at idle and my dads one is more like half of that so they machined a sleeve and inserted it into the pipe in an attempt to build up preassure to the injection and slow it down going back to the tank this hasnt helped . According to the dealer there is nothing that controls the return valve on the fuel line but my dad says there are 3 plugs going into it which then go to 3 separate boxes, the mechanic is convinced the problem exists with one of these boxes but the dealer doesent think they exist. I was also reading about some of the other threads with similar problems but i am not sure if the problem worsens with heat i dont think so but i will ask him to feel the ignition control unit if it cuts out when hot and tell me if there is significant heat.
They did think it could be a fuel pump error but the pump has just been replaced and the mechanic as far as he can see thinks its operation is fine.

Thanks to anyone that can help

Andrew Wright

ps Can the lambda box have this effect over it ?

 

[smokeme]

I would look at clogged fuel filter or lines, bad fuel pump, bad fuel pressure regulator, or clogged injector. I don't think there is a way that the lambda could cause a low fuel pressure, the fuel filter is the highest suspect they usually cause a stumble when we press the gas quickly.

 

[Morty Mort]

Hei.

This reply is the worst scenario. But it is a straight forward job.

The head gasket might have blown between two cylinders. This caused a backfire on my Uno 1.1 ie 1108 cc 1993 model. Try idling the car on 3 cylinders - make a cycle of differnt alternatives. This FIRE engine runs smoothly on 3 cylinders. In my case the engine eventually refused to run on 4, but ran fine on 2 different setups of 3 cylinders.

If so, do a compression test. If you get 4 equal readings, the gasket is propably fine, but if you get low readings on two cylinders next to each other, suspect a blown gasket. This will lead to an ignition of an uncompressed air/fuel mixture which will work against the rest of the engine...

So, a gasket change is in place.

Else check plugs, HT-leads, filters as mentioned. Check that the oil breather hose is not clogged - it might be contaminated with old oil/dirt in the brass filter within it. Clean the injection unit, because the oil breather lets out hot fumes and dirt in it.

Morten.

 

[Morty Mort]

Another symptom of backfiring might be a cam that doesn't open the exhaust valve. This happened on our Ritmo Abarth. The cam was worn out due to overheating. Open the rocker cover and look inside. All eight cams in order? Then problem is elsewhere.

Morten.

 

[awright58]

Hi All

I dont think it has a leaking head gasket the engine has recently been overhauled and all these things were renewed but it doesent idle properly it idles fast and rough, as for the backfiring my dad recons it does it because it cuts as you are driving and i think fuel builds up in the cylinders then it decides to fire again and the fuel ignites bang ! the car doesent backfire when you are not going only if it cuts out while you are driving i think it sometimes does it. As for the injector it should be clean as the mechanic has tried everything including that, my dad took it to an ignition specialist who said that if he could get the specs for the engine control unit he might be able to sort it out it is a box in the dashboard apparently it is a bosch unit PART NUMBERS 0280 000 732 and 764 7 555 this guy says he needs a wiring diagram and the specifications of proper operation conditions for the box
although he doesent think it is faulty

Thanks for all your help

 

[awright58]

i dont think it is the cam as the other day it worked fine for a couple of days but it is back to normal now so i think it wouldnt be able to do that if the problem was mechanical

 

[Morty Mort]

That´s good news.

Check on the back of the injection module. The throttle cable is winded up on a spindle there. Does this spindle thing punch in the idle plunger when idling? The idle plunger is a black rubber button on the rear side of the SPi module. If not, try to depress it and see if the idling normalizes. I had this problem earlier. The throttle cable was not slack enough to depress the idle plunger, and the car idled roughly and stopped and jerked and stalled at red lights and even between slow gearchanges.

Morten.

 

[Morty Mort]

I have no experience with the fuel system, except from changing a fuel tank. But the fuel relays are connected under a plastic shield by the coil somewhere. Unscrew the bolt - think it can be done with your fingers, and pull off the shield. I remember reading of how to test these relays in a manual a long time ago. Maybe someone else has some experience with this. Anyway, pull them out, check for corrotion etc., brush and refit.

Morten.

 

[awright58]

HI all
by the sounds of it after talking to my dad it seems that the ignition specialist said that there is a fault in the system somewhere i dont think it is the plunger bit you are talking about because yes it does idle rough then you can be travelling along normally and the thing just cuts out then starts running again or worst case scenario wont start for half an hour then eventually starts i did tell my dad about the other guy who found it was that small box on top of the coil was overheating but the ignition specialist guy says that is fine he seems to think there is a breakdown on one of the wires going to the box he calls the ecu which is located under the dash on the right hand side i gave the part number in the previos thread , he usually deals with high performance cars but says he thinks he can fix it if he could get hold of a wiring diagram and the specifications of the sytem temperatures etc if this makes any sense . the car does not get affected by the temperature it can cut out when just started or after an entire day. The funny thing is the heater fan was not working and then he got an auto electrician to fix it but now it has stopped working , i am wondering if there is a short somewhere that is playing havock with the engine management system is this possible ?

Anyway thanks for listening, any help is much apreciated

Regards

Andrew Wright

 

[Morty Mort]

Back to the backfire. If there is an ignition problem within the distributor, it might just be the cap and rotor. Are the distributor cap worn? They wear out just as plugs and HT leads, and can short.

I've never heard of the ECU failing on a MkII Uno 1108 cc. It's located as you say within the coupe on the passengers side (in Norway).

According to the fan, have you checked the fuse "box". Fiddle a bit with the relays and wires to see if the fan starts again... good old Fiat Ritmo Abarth trick.

I'm in some sort of darkness here, but there might at least be some ideas of what to remove as potential problems...

Morten.

 

[awright58]

hi again

The distributer cap is new i got that when we did the overhaul, as for the fan i will ask my dad to have a fiddle i am not sure it is a mk2 it is one of the last unos produced but it has an 1108cc engine the backfirig i think occours because of a buildup of fuel in the cylinders or the exhaust because the engine is turning but not firing ie if you were to drive down the road and switch off the ignition and let the engine be turned without firing then turn on the ignition it will start to fire again and maybe this causes backfiring because it ignites all that unburnt fuel at once i know it is possible in a carburater car as i have done it so it could be possible in an uno but have never tried. the ignition guy says he needs firstly a wiring diagram and secondly the specifications of correct operation ie lamba temperature and this voltage and that voltage ( i have no idea ) as he must have some machine that can fix these things and diagnose the problem, he doesent seem to think the thing is faulty he seems to think there is a fault on one or some of the wires leading to the ecu not the unit itself so it is causing the unit to make the engine run badly i dont think it is mechanical as it just goes and comes back then sometimes it doesent start for ages sometimes it starts straight away, it idles fast and we cannot get the speed down and it doesent rev as as soon as it does it wants to cut out but not as it would from starvation just bang off then bang on kind of thing there is no drain in power you would expect from a blocked injector or worn cams i think it revs ok when not in gear but i will ask. thats about all i can say

Thanks again for your help

 

[alexGS]

Sorry I'm not going to be as much help as Morten here - I am slightly lost in all the descriptions... and I don't have experience of SPi injected Unos.

But idling fast and rough sounds like a vacuum leak? Rather than suspecting the lambda sensor and ECU, has anyone checked/replaced the throttle body mounting block or any other point at which air could get into the system? For example, I have read that on FIRE engines, the inlet manifold can easily distort and allow air in between the manifold and the cylinder head. Perhaps you could remove it, have it skimmed, and refit with some red Loctite Master Gasket (stuff in a syringe).

One way to find a vacuum leak is to spray WD40 around the suspect areas - the engine note will change when it finds a way in!

Bear in mind that a vacuum leak will throw the lambda voltage off, and therefore make you think that the sensor is faulty when it isn't.

Your comments about the fuel pressure have me concerned as well. Is it now within the quoted limits after replacing the filter etc.? If not, the problem may be related to the vacuum leak, since the fuel pressure regulator returns excess fuel to the tank based on the manifold vacuum pressure.

Those boxes associated with the return line are probably part of the evaporation control system - perhaps you can bypass these. Figure 13.46 on page 13.74 of the Haynes manual shows the layout. It looks like you could just remove the pipe from the Elbi solenoid and plug it. That would eliminate the risk of a leak (allowing air in) at either of the two solenoids or the carbon canister.

I have heard people say that nine times out of ten, an apparently complex fault with fuel injection has a very basic cause. Do not be tempted to suspect the 'black box' components until after you have eliminated all simpler causes...

-Alex

 

[Louie Bee]

I have heard people say that nine times out of ten, an apparently complex fault with fuel injection has a very basic cause. Do not be tempted to suspect the 'black box' components until after you have eliminated all simpler causes...

-Alex

Sound advice there Alex