Hi all

Am trying to source the issue that is causing my 2003 1.9 JTD to run rough. It runs fine once over about 1500 revs. So far have cleaned the EGR (now put blanking plates on both ends of the connecting pipe) which has got rid of the black smoke from the exhaust. With engine running I disconnected each injector lead, looking at them left to right as you stand in front of the engine bay the one furthest left (drivers side) made no difference when disconnected, the other 3 caused the engine to stall so there's obviously an issue around the first injector. I then went to the guide for testing electrical circuitry for the injectors. Not sure I followed it right as the guide is for a slightly different model.
I put my multimetre onto each injector and got the same resistance reading for each one which i think suggests the soleniod in each is fine. I then disconnected what I think is the D81 plug, situated at front of engine down by the bottom of the radiator, it's sitting on top of what looks to be part of the air flow system? The guide talks about the earth lead being obvious as it is the thickest, of the 5 wires going into my plug all were the same size. I made the assumption that the middle wire is the earth (coloured solid purple). I got totally contrasting resistance readings? Below are the colours with the corresponding readings:

white = 9.95 k ohms
white/green = 0.84 k ohms
purple = earth (i think)
black/white = 90 k ohms (this reading kept either dropping or increasing until out of range on the metre setting)
green = 2.12 k ohms

I'm either doing the test wrong or there's something seriously up with the wiring?? If anyone out there can help I'd be very grateful, just had a big bill for the other family car so could do with sorting this one myself.
Can provide pics if that would help explain what i'm looking at??

Unlike the 1.6 engine guide you're following, the JTD 8 valve engine does not have a D81 connector. From the wiring colours and location you mention, I suspect you're mistakenly testing the 5 pin airflow meter connector (K41).

As with most current engine management systems, none of the Stilo engines have permanent earth connections to the injectors. The JTD 8 valve injectors (N70) get their power supply from pin 117 (injectors 1 & 2) and pin 118 (injectors 3 & 4) of the engine management ECU (M10). The ECU sends negative (earth) signals from pins 119, 120, 121 and 114 to injectors 1, 2, 3 and 4 respectively, to fire the injectors.

Wiring diagram for the JTD 8 valve injectors is below along with the wiring colour codes chart, however the colour codes shown on the wiring diagrams are often wrong. The 2 diamond shape symbols below pins 117 and 118 of the diagram are soldered joints within the wiring loom.

The ohmeter part of a multimeter measures resistance by injecting a voltage (usually from its 9 volt battery) into the circuit. Most ECUs work with 5 volt signals, so there's a slight chance that you've damaged the ECU by connecting to the airflow, or any other sensor's connector, if the ECU connector was still connected to the ECU.
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Thanks for the diagrams and info, really useful to know. hopefully the ECU is still ok as engine is running the same as before with no errors messages coming up on the dash.

I'm ok on mechanics but not so on auto electrics, do you know of any guides or threads on the forum that may be able to help diagnose and fix the problem? I've been searching but not found anything on the forum so far.

Yoinks! Too much "digital" and not enough "analogue" going on.

The most likely thing to go wrong, is by definition "the most likely thing to go wrong".

Are you sure the problem is not just the injector?

Take the injector out of number 4 (which we thinks works).. put it in number 1 (which we thinks doesn't).

See if problem still exists on number 1 .. or whether it has moved to number 4.


Ralf S.

Was thinking the very same, once it crossed my mind was obvious how obvious it was!! On my list to do this week, will hopefully report back that it’s simply the injector! Cheers

well finally got around to swapping the injectors. Initially thought injector 1 not working/wiring faulty so tried swapping it with injector 2. After a bit of head scratching and knuckle scrapping got both injectors out. Unfortunately didn't notice all the crap that had collected around the base of the injectors until too late! I suspect some debris has dropped down into the cyclinders now. Carried on regardless and swapped the 2 injectors around, wouldn't start. looked to be fuel coming out of somewhere as it was clearly visible around the area of the injectors 1 and 2... Took it all apart again and spotted the likely issue, injector 1's copper washer was still located at the bottom of the hole where the injector sits, when i'd put the other injector in place it had its own washer plus the one that was stuck down there from the injector 1. could not shift it so had to put injectors back in the way they were.

Engine now turns over but won't fire. My worst fear is that muck has got into the cyclinders which is now preventing the car from firing, at best i'm hoping the fuel has got into an electric connection somewhere and it just needs to dry out....any advice would be much appreciated...am I looking at an expensive engine strip down to clean out potential dirt??

I don't think so.. bits of dirt are usually quite soft so if any grains fell into inlet manifold they would be sucked into the cylinder and then burnt or ejected down the exhaust.

You would have to be spectacularly unlucky for a hard piece of debris to get wedged in the valve, jam it open and causing it to get smacked by the piston. But even this won't stop the engine from starting.

Go back a step. Make sure that each injector is properly seated and that you have a spark at the connector (i.e. that injector is getting some juice). I'm guessing that something has been disturbed (fuse, relay etc.) and the injectors aren't getting a signal any more.

The glass bulbs without a metal cap (just metal tangs folded over each side .. "T5" I think... ) are dead handy for testing injector wiring, if you don't have a meter. Unfold the tangs and stick on in each terminal of the injectore connector. When you crank the engine, the bulb should flicker.


Ralf S.

Thanks for the feedback.

Glad to hear that it’s unlikely to be dirt in the cyclinder. Have been trying to think logically as to what the problem is because as you say it does seem that a spark isn’t getting through, can only imagine I’ve knocked something whilst removing the injectors. I do have a multi meter so will see if a charge is reaching the injector. Did wonder if maybe some sort of immobiliser has been activated as that’s what it sounds like, could that also be a possibility?

Thanks again for the help, it is appreciated

I can't imagine how the immobilisor might be interfering. If you have the key and the code is valid (sometimes dead batteries can confuse the ECU) then it'll go.

If you're getting sparks at the injector, the next thing to check is whether they have any fuel to squirt. A fuel pump relay, fuse or shut-off (button inside the passenger door) might have been tripped by any unexpected electrical surge.


Ralf S.

Definately fuel getting through.

Put multi meter on injectors 1 and 2 and both show a reading although the current gradually drops?

Spoke to a mechanic friend who suggested that some injectors require recoding/matching up with the vehicle, he even said that once an existing injector is disconnected it will need recoding again. I assume someone would have already pointed that out if it were the case?

I never heard of having to recode an injector, just because it got disconnected... but if such a thing exists, then it ought to only affect the very newest stuff.

I *can* envisage having to calibrate the injector to the ECU but this is more for efficient operation... and if you put an injector back where it came from, that ought to be enough to keep the ECU in perfect sync' with each particular injector.

But your car doesn't start at all. It has to be something else...

On the other hand, you have some juice at the injectors.... so it's not a TDC sensor etc. issue.

Does the current fade at the same time/whilst you are cranking it, or does it give a peak reading that dissipates when you stop cranking? The latter would strike me as what you might expect. The former would be more counter-logical.


Ralf S.

I didn't crank the engine, simply turned the ignition on and the reading steadily dropped. I assumed I only needed to check that current was reaching the injector, do you think I should try turning the engine as well?

Make sure you keep yourself/equipment out of any pulleys etc... but yes, try cranking the engine over and see what happens to the injectors.

It might be illuminating .. (do you see what I did there? ) to know whether the injectors are getting a signal while the engine is cranking. If the meter/bulb flashes, then the injector should work.

If you get a signal, that would rule out an immobilisor problem, since the immobilisor prevents the injectors from working.

It would also rule out a TDC sensor issue (since that sends a signal to the injectors when it's time for them to do their thing). A brief signal just when the ignition is switched on would just be an ECU start-up/diagnostic check.

Immobilisor activated should also give you a "key" code warning light on the dash. It'll stay illuminated and flash rapidly when you're cranking the engine, or something similar. You'd notice it anyway. Hopefully not an immobilisor issue though.. that's just extra complication at the moment..


Ralf S.

tried turning the engine over and looks as though nothings coming through to the injectors (only checked 1 and 2). Forgot to mention that when I first came to take the injector out I removed the rocker cover as I thought I needed to to get at it, wondering if i could have knocked something in the process?

I noticed some damage on the cam sensor lead also, doesn't look to have effected the internal wire but have included a picture to get a second opinion.


Any advice on where to look if no signal is getting through to the injector when turning it over? I looked around the engine bay in the areas where I've been working to check for any loose or knocked connections but can't see anything.

Is there a fuse associated with the firing that could have possibly blown?

Hmmm... On the other hand, at least we know why it's not starting.

I'd guess that a relay has been disturbed or a fuse has been spiked and didn't like it.

I don't have my User Manual handy.. but the relay is most likely one of those on the battery, so probably didn't get dis-lodged by accident, since it's the other side of the engine bay.

More likely a fuse has blown, while you were probing. As above, the fuse will be one of those on the battery pack... so just have a look at each one to see if they're all intact.

I doubt the TDC sensor itself is knacked, although it should be possible to check whether the plug feeding it is "live", to isolate the fuse/relays or the sensor itself. I have no idea how to test it though. I suppose it must have an "in", an "out" and a return signal wire... but it's electrickery, so makes my head hurt.

If the fuses all look okay though that's what we'd need to find out. Is the TDC sensor getting a signal or not... (and is it feeding anything back)?


Ralf S.

Ralf S.

Thanks for the feedback Ralf S.

Bit the bullet and finally got my mechanic to come have a look today. He ran a diagnostics and one of the faults mentioned a plate heating thermostat relay, new one on me but my mechanic reckons it's not the problem. After some fiddling about he discovered that the fuel isn't being fed properly or at all. We checked all the fuses in the engine bay, all fine. Eventually got breakdown to take it to his workshop to have a proper investigation.

Something worrying that he said though following a chat with his 'injector friend expert' who reckons if i've taken any injectors out then we need to stop trying to fault find and just replace all 4 injectors! Apparently injectors can be damaged simply being exposed to air, let alone being spoilt if wiped clean (which is what I did). I'm sure one of you guys would have mentioned this if that were the case, I've read a thread on here where someone swapped injector 1 and 2 around (what i did) with no mention of potentially condemning the injectors by doing so. The thread never reached a conclusion so don't know how that one ended up?

If the 'injector man' is right then the cost of replacing all 4 injectors would exceed the value of the car which would effectively mean scrapping it. Hopefully one of you can tell me he's got it wrong?

mexnick said:

Spoke to a mechanic friend who suggested that some injectors require recoding/matching up with the vehicle, he even said that once an existing injector is disconnected it will need recoding again. I assume someone would have already pointed that out if it were the case?

Click to expand...

The JTD injectors are tested and graded by Bosch (the manufacturer) at the end of their production line. The grade is marked as a code on the top of the injector as in the diagram below. When the injectors are fitted to the engine, and the engine fitted to the car by Fiat, the car is connected to a computer which programs each injector code into the Engine Management ECU. The EM ECU can then adjust the amount of fuel delivered to each injector depending on the injector's code. When new, the engine will usually be fitted with all 4 injectors bearing the same code. If an injector with a different code is fitted, that injector can be individually programmed into the EM ECU. If you remove and refit the same injector to the same position, the EM ECU does not need reprogramming. If you swap 2 injectors bearing the same code, then the EM ECU does not need reprogramming.

mexnick said:

Bit the bullet and finally got my mechanic to come have a look today. He ran a diagnostics and one of the faults mentioned a plate heating thermostat relay, new one on me but my mechanic reckons it's not the problem.

Click to expand...

Plate heating fault codes on the JTD engine usually refer to the glow plug relay, but can also refer to a faulty glow plug or wiring. Unless the car is in a very cold environment, it won't stop the engine from starting.

mexnick said:

Something worrying that he said though following a chat with his 'injector friend expert' who reckons if i've taken any injectors out then we need to stop trying to fault find and just replace all 4 injectors! Apparently injectors can be damaged simply being exposed to air

Click to expand...

If the injectors can be damaged by exposure to air, then how do the engine assemblers install then in the first place? And how could any mechanic ever replace a faulty one with a new one?

It would be interesting to see how his 'injector friend expert' could replace all 4 injectors without exposing them to air.
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I've had injectors out... sent off to be cleaned (basically run through with some solvent liquid) and then put them back in the car without any trouble (although in the same location). Usually life is not so complicated, so what Davren wrote about the injectors and their codes sounds more likely. Even fitting an injector in the "wrong" place must still work, albeit it might not be "optimised" for best performance/economy.

If there's no signal at the injectors, then they won't "fire" regardless of anything else. That has to be the first thing to solve.


Ralf S.

Thanks for the responses. All thats been said makes sense, I can only guess the 'expert' probably has a broad knowledge of injectors and has hopefully got it wrong with regards to the stilo. That's very useful info regarding the codes for each injector.
My mechanic won't be able to get onto my car until next week or possibly the following. I'll tell him the info provided here and hopefully it'll be a relatively easy fix (have bought a recon injector off ebay)....I'll post results as a follow up for others.

thanks again for the help!

the car is now back running better than ever before. I'll go through what my mechanic did as per his invoice:

-Checked/Bleed fuel supply from pump in fuel tank to injectors (poor at injectors)
-remove fuel separator & pipes & clean out
-remove high pressure fuel pump regulator solenoid & clean & rebuild
-fit second hand injector (one i supplied bought from ebay)
-clear codes
-reset

hard to know which out of the above solved the problem? could be i dislodged something whilst getting at the injectors? is certainly running better than it was previously, doesn't feel like it's missing anymore.

Thanks for the advice and help with this one!