Injector failure modes?

Firstly, Hi to all as this is my first post.

Jug; you seem to be the guru on these cars

My g/f's car is a 1996 Bravo 1.6 - I've done a lot of reading on this and other forums, the car has an intermittent fault which brings on limp home mode. I can't track it down to any particular failure scenario. I've changed the thermostat and housing as it was running cold. Sure enough the stat was stuck open on removal. However, that didn't cure it though made the car lots better.

My question is this, the injectors seem to be a favourite failure on these engines. Reading mine three are around 17.4 ohms with one being 14.3. How does the ecu monitor them? Individually? From what I've read these figures are within tolerance but will the fact that one is so far from the other 3 cause problems?

(For the record car has had the following checked or replaced - ht leads, spark plugs, fuel filter, coolant temp sensor, icv, iats, lambda and tps. Some of these were changed because they had to be through clear faults and not trying to chase limp home problem. Next step is to have a diagnostic carried out if the injector readings are inconclusive)

Regs, Simon

hi simon,
the ecu doesnt monitor the injectors, thay could all be compeltely dead and the ecu wouldnt know about it. this is why dealers and garages have so much trouble diagnosing injector failure. if one injector begins to fail there will be a misfire on that cylinder, the ecu can detect that. it causes the engine to run on 3 cylinders (feel like limp home mode) and the injector light to illuminate (ecu detects misfire and illuminates light).

your injector resistances show that one injector is significantly different to the others. this will be causing uneven running (and hence a loss of mpg and performance) at the best of times. when injectors begin to fail noticably it is often intermittent, so imo your problem could be an injector fault. you've tried so much already that it would make a lot of sense to try fitting a scrapyard injector with a resistnace very similar to the other 3 before you give up and pay out for a diagnostic. replacing an injector is easy to do and will only cost you £5-10 for a scrapyard injector if you remove it yourself.

Thanks for the reply.

The more I think about the way the car behaves, the more I think it is that injector. The ecu seems to carry out a 're-check' every few minutes; this seems to be a regular event if you see what I mean?

The car will drive ok for about 10 mins, then go into limp home, then the ecu will cycle the limp home mode. I strongly suspect the ecu tolerates a certain number of misfires before bringing the limp home mode on. Then after a couple of minutes it will clear limp home mode and run normally. I can feel the car very very slightly misfire (lumpiness) then it will go into limp home mode.

When running ok, the car is very torquey throughout the rev range. I'm quite impressed with it considering it's only a 1.6 litre.

the 1.6 engine is called "hi-torq" by fiat because it has such a good torque coruve for the capacity, and i agree for a 1.6 it certainly gets the car moving with ease.

Hi Jug,

Finally got around to changing the injectors. Sourced from SCI. Got all four for £200 plus vat.

They all read perfectly resistance wise. Car is still going into limp home mode though.

Like I said before, I've changed the plugs, leads and checked the coil. The primarys on the coil are both spot on 1.2 ohms. Not within spec according to the Haynes book of lies but both equal. Secondaries are equalish too.

When the injector light comes on and the car runs roughly I've tried removing the plug leads in turn. The only one that makes a difference is no.1 (engine stalls). Leads me to believe its not coil pack as three cylinders appear not to be firing??

The car has probably done 60 miles with the limp home mode coming on and off. I've pulled the plugs and they're mostly super white which indicates lean running obviuosly. The plug leads have resistances in keeping with their lengths if you see what I mean and still look brand new.

Do you think the plugs could cook out in such a short period? I'm typing this at nearly 7pm and all the motor factors are shut

its time to clear the ecu's fault codes, then drive it until the fault happens again, then read the fault codes.

or you could just read the fault codes to save time and money and we'll apply a bit of common sense to see which ones need to be ignored as old codes (if any)

Hi Jug,

No need. I fitted some new plugs today and drove the car as much as possible. It went into limp mode while driving once which was accelerating under load. It felt just like a plug lead giving out. Normal service was resumed more quickly this time though until later on......

Parked it up outside a friends house after a 5-6mile drive. Came back to it after about 1-1.5 hours and it started up but straight into limp home mode. I thought "Right y'bugger!".

I went straight back to the garage and got out trusty multimeter (left car running). Before turning it off, I checked the plug leads again by pulling each in turn. Only No.1 was firing this time. Pulled it and engine stopped.

I immediately then checked the coil primaries. Top to middle pin was 0.8 ohms, middle to bottom was out of range on the 20ohms scale. Had to dial up to the 200k range to get any sort of reading.

A few minutes later, the 0.8 primary winding was up to 1.2 but the other still way up there in the 200k ohms range. I forget the actual reading.

Haven't changed it yet but I think safe to say a heat soak induced failing coil pack?

In hindsight, I should have spotted it before as only no.1 was firing and they're paired coils aren't they! D'oh!

yep

Changed coil pack today. Put lots of stress on car with city traffic and motorway traffic. Not one hiccup! Problem solved. Thanks for you help matey.