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Discussion Starter #1 (Edited)
HELP! I am getting the dreaded MCSF warnings at random with the above codes showing on my 156 JTS. I've just replaced cylinder 1 coilpack with a brand new Bosch item and have sprayed all electrical connectors on coilpacks and lambda sensors with contact cleaner to no avail. The car is running and idleing perfectly no misfires or hiccups. It doesn't go into limp mode or change how it drives when the warning comes on.
If I erase the error codes the car will go for between 2 to 70 miles before the MCSF returns.

Any advice as to what I should look at next? I suspect a dodgy electrical connection somewhere is causing this, but where???

Any help would be much appreciated, thanks in advance. The car has done 82k miles
 

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The P1151 and P1175 code are probably due to misfire so nothing to be too concerned about.

The P0351 is ignition as you already know. The best place to start is the coil pack multi plug. I suggest getting at least 1 male spade terminal to push into each terminal of the multi plug. I think the size is 2.8mm (not the larger 6.3mm which used to be common). These are things you may have or can get at Halfords. Push a terminal in and feel if it is tight and getting a good connection.

Short term, it may be possible to use a small hooked pick or similar to tighten the terminal spring. Long term, I have yet to find the correct terminals or new multi plugs in kit form for the coil packs.

As a bodge, it may be possible to space out a weak spring terminal with a few strands of wire as long as the wire does not sit out and cause a short circuit (which would be very bad).

If terminal springs are good, then it must be a terminal in the ECU multi plug, I guess.
 

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Alternatively, add a tiny bit of solder to the coil terminal to make it larger to compensate for a weak terminal spring.
 

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Discussion Starter #5
Replaced one of the coilpacks (the non-Bosch one) and now only getting the 1151 code intermittently? Nearly there...Any ideas?
 

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That's a shame. The P1151 is sensor 1, bank 2 (which should mean pre-cat wideband sensor for cylinders 1&4). The fault description contains the word "lean" which really means that a fuel injector has an affected fuel spray.

The JTS does have poor injector spray patterns fairly often due to the injectors being in the combustion chambers. Even though there is probably only 1 injector which triggers the fault code, if it was me, I'd have them all taken out and serviced (tested, ultrasonically cleaned).
Unfortunately, the JTS injectors are a pain to remove.

A strong mix of fuel cleaner may help but I wouldn't rely on it to completely sort all the injectors. It is one of the reasons why Shell V-Power, BP Ultimate etc are often recommended for the JTS. When I had the injectors tested and serviced on my JTS at 101k miles, the specialist wanted to know how the injectors were in such good order.
V-Power was the answer.
 

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Had this on our GT JTS. Took it to 2 or 3 local specialists and they did what you have done to no avail. Took it to Jaime Porter at the Alfaworkshop and he diagnosed a faulty injector and had it fixed that morning
 

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Discussion Starter #9 (Edited)
Thanks guys, I was already suspecting an injector was the likely culprit. I'll try a heavy dose of injector cleaner first....fingers crossed.
Just as a matter if interest what's the approx cost of injector removal, testing and servicing (he says holding his breath!) ?
 

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I'm not sure how much it costs.
I'd guess around 4 hours work.
I got my JTS injectors done for £90 but even £150 for all would be a decent price (plus removal and refitting labour).
 

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Thanks guys, I was already suspecting an injector was the likely culprit. I'll try a heavy dose of injector cleaner first....fingers crossed.
Just as a matter if interest what's the approx cost of injector removal, testing and servicing (he says holding his breath!) ?
I honestly can’t remember, but I remember thinking it was a reasonable price. Mr Porter told me they’d got a mechanic with really small hands that made the job a lot easier!! 😂
 

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Discussion Starter #12
Well, just a bit of an update. Purchased some "Genuine BG 44k Petrol Fuel System Cleaner" not cheap at £23.45 on fleabay but this is the one everyone says is the most effective so thought it might be worth a punt mixed with a tankfull of Sainsbury's super unleaded. I also took the two main bulkhead multipin connectors apart and gave them a good dose of contact cleaner. Due to lockdown,cold weather, snow, ice, salt covered roads etc the JTS hasn't moved much. Have been out twice in the last fortnight (50 miles or so) and so far so good and car running very sweetly with a lovely even idle and (touch wood) no warning lights. Such a lovely car when it goes properly...
Obviously early days but signs are hopeful. Will keep the thread updated in coming weeks, fingers crossed!
 

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Discussion Starter #13
Well, the car continues to perform and drive well with no with discernable misfires and a nice steady idle but am still getting code 1151 intermittently and today for the first time code 0420 appeared at the same time. Thoughts anyone??
 

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P0420 is a catalytic converter low efficiency code. It won't be an inefficient cat but it will be a symptom of an affected fuel injector spray pattern. It should be a sign that things still aren't right and actually seem to be getting a little worse. That being the case, it is time to start planning having that injector cleaned or changed for a new one.

As you had a coil issue (as many do), I'll again take the opportunity to mention I finally identified the terminals in the ignition coil multi plug housings. They are Bosch BDK terminals but I did a post about that.
 

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Discussion Starter #15
P0420 is a catalytic converter low efficiency code. It won't be an inefficient cat but it will be a symptom of an affected fuel injector spray pattern. It should be a sign that things still aren't right and actually seem to be getting a little worse. That being the case, it is time to start planning having that injector cleaned or changed for a new one.

As you had a coil issue (as many do), I'll again take the opportunity to mention I finally identified the terminals in the ignition coil multi plug housings. They are Bosch BDK terminals but I did a post about that.
Thanks again for the reply. Yes you are correct I did replace one coilpack (cylinder 1(?) on extreme left when viewed from front of the car). No coilpack warning codes since. Is it possible to identify which injector might be the culprit or would you recommend removing them all for testing/ reconditioning? Appreciate your help/sharing of knowledge
 

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I can't say for sure but....
The P0420 code specifies bank 1 (cylinders 1&4) so half way there.
If you have a diagnostic tool which can show live data under the EOBD system (I cannot remember if live data under the manufacturer's system shows this), I would look at the figure given for fuel trim.
Fuel trims should all be as close to zero as possible. I would expect the affected injector to display as a figure furthest from zero on cylinder 1 or 4.

That is best guess though. Ideally I'd like to see all the data but in trying to be helpful, I think that may be enough to identify the worst injector.
 
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