Cylinder 8 running cold

[angus337]

Started the car up for the fist time after installing new ACT performance manifolds. After heating up all the manifold pipes have started to change to a nice gold colour except cylinder 8. Checked the temperatures with an IR digital thermometer and cylinder 8 is running really cold. So looks like its only running on 7 cylinders.

Also noticed wideband is reading rich AFR~12.1, with the wideband connected to the nearside manifold, but much leaner AFR~14.6 with the wideband connected to the offside manifold. The idle AFR was previously mapped to about 13.3 with the original manifolds and the wideband located in the Y piece.

Checked the plug and it looks ok and wasnt wet, also checked the leads and its definitely getting a spark.

Since its getting a spark and is running lean on the even cylinders, I thought it must be the injector. Swapped injectors with cylinder 6 and it made no difference, so I'm pretty sure the injector is OK. I don't have a noid light to properly test the injector wiring, but I am getting 12v at the plug.

Not really sure what to check next, without starting to pull it apart to check the cam / rockers / push rods etc. Any other ideas?

[angus337]

Steve_D said:

There should be 'just' enough wire length to switch the 6 & 8 injector plugs so worth testing that.
Also check that the pins in the plug have not pushed back. Also check the pins in the injector are not corroded. The are actually steel and I have seen them completely rusted away.

Steve

thanks Steve, looks like the cylinder 6 plug will just reach the cylinder 8 injector, so can try this later

[angus337]

blitzracing said:

You wont get a sensible lambda reading if a cylinder is not firing.

Agreed. Although it does make sense that it was running lean in the offside bank if cylinder 8 is not firing. What worries me more is that the nearside, with 4 'good' cylinders was running so rich. which could indicate that it has been running like this for a while.

I've done some mapping recently, prior to installing the new manifolds, the wideband located in downstream of the collector. If it was only firing on 7 cylinders then, I expect it would have added fuel to the 7 running cylinders to meet the target AFR, which would explain why the nearside is now rich. Weird thing is though that the car was running really well,

Edited by angus337 on Monday 19th October 11:23

[angus337]

Zener said:

While its running put a long screw driver to your ear on a known good firing inj noticeable click click click so you know what your listening for
then move to No.8 to see if its clicking/being fired by MS but like mentioned in Tunerstudio you have "Output test mode inj/spark" just make sure you disable the fuel pump or you could potentially hydraulic lock the cylinders whilst using this test sequence , you can use the stethoscope/screwdriver method for this too

I did try the screwdriver test, I could hear the injectors ticking, but cylinder 8 did seem fainter, and I could have been picking up the noise from the other injectors or rockers. I'll try the test mode in TS as this should be more conclusive without the background noise of the engine running.

Edited by angus337 on Monday 19th October 12:01

[angus337]

QBee said:

Shirley the nearside is running rich because the ECU is trying to bring the total AFR into line with its correct settings. With only 7 cylinders firing, and no fuel in your number 8 cylinder, your engine is bound to be running too rich on the remaining 7 cylinders to compensate?

At idle it runs in open loop, so the ECU is not trying to adjust the fuelling. However when it I last adjusted the the fuel map I set it to give about 13.5 AFR at idle, if it was running on 7 cylinders at the time then these would have to have been set-up too rich to compensate for cylinder 8.

[angus337]

angus337 said:

Steve_D said:

There should be 'just' enough wire length to switch the 6 & 8 injector plugs so worth testing that.
Also check that the pins in the plug have not pushed back. Also check the pins in the injector are not corroded. The are actually steel and I have seen them completely rusted away.

Steve

thanks Steve, looks like the cylinder 6 plug will just reach the cylinder 8 injector, so can try this later

Managed to start it with cylinder 6 injector plug connected to cylinder 8 injector. The car started OK but cylinder 8 was still cold. Only ran it for a few seconds, but approx offside temps as follows: C8 - 42C, C6 - 28C, C4 - 78C, C2 - 82C. Seems a bit strange that C8 was hotter than C6 though, would this indicate that its still firing but very weak?

Think its time for a compression test. Hopefully get the kit tomorrow.

[angus337]

I might be clutching at straws here, but one thing I noticed when swapping over the injector plugs was that the injectors don't seem to be seating well on the offside, particularly cylinder 8, which does seem a little loose. it seems like the fuel rail isn't sitting low enough to properly seat the injectors. If there was a vacuum leak at at the injector seat, could this be causing the issue? it would certainly cause that cylinder to run very lean and miss at idle, but possibly run OK at load?

[angus337]

Zener said:

This is true , do your style injectors have the two grooves at the top for the retainer clip? Because only one will work correctly the other will pull the inj to high and out of its opening and into the tapered part used for leading in the inj O ring , quite sure you would have spotted this height difference sooner compared to the rest it would also introduce an air leak into the whole intake plenum too

Edited by Zener on Tuesday 20th October 10:52

I'll recheck this afternoon, but pretty sure its clipped into the incorrect lower groove. I'm using these injectors:

[angus337]

NZ fan said:

not sure what coil packs you are using but is there a chance you have no.6 and no.8 leads interchanged?

I'm using the Gems coils packs which sit behind the Plenum. The leads are definitely connected correctly although I am planning to swap out the cylinder 8 lead anyway to test it just in case.

[angus337]

So the injectors were fitted incorrectly, with the retaining clip in the lower groove. I've managed to reseat the injectors on the offside, with the clip located in the upper grove, and its now running fine. Cylinder 8 came up to temperature with the others. Didn't run it for long as still need to do the near side injectors and tidy up the plug leads, but AFR now looks good on that side.

My concern now is how long its been running like this and if its likely to have caused any damage. I re-fitted the injectors about 18 months ago and pretty sure they were securely seated at the time.

I did have to adjust the engine mounts when I was fitting the new manifolds, to get some additional clearance where Y piece passes through the chassis. So maybe this caused the issue?

[angus337]

Finally had a bit of time and some better weather yesterday and managed to get the car out for a run.

The car idled well up to temperature and the AFRs pretty good on both sides. However the engine died the minute I blipped the throttle. From the logs, it seems that the idle valve was closing in too far, when dropping back to idle. I’d previously tuned the closed loop idle to use the initial value table, which was closing the idle valve too far, causing the engine to stall, before the idle control kicked in. I changed the setting to ‘use last value’ which solved the issue (ill have to retune the initial value table later).

I guess this proves that its been running with the injector vacuum leak issue for a while, at least since I tuned the closed loop idle earlier in the year but more likely since I refitted the injectors about 18 months (2k miles) ago. Not sure if this would have caused any damage to the engine, I’m hoping that this is only an issue at idle, and once at load with the throttle open, the cylinders will have been more closely balanced. I'm still planning to do a compression test, but the kit I ordered wont hold the pressure, so now waiting for a replacement.

On a positive note, on the short drive I managed, the car drove well and the tune wasn’t out by much, other than a bit too rich just of idle and on overrun. Amazing sound from the new manifolds, although possibly a bit too loud!

[angus337]

VerySideways said:

What are you running throughout?

I've got the ACT long primary manifolds, the sports cats, and the ACT cherry bomb system. It's not quiet :-)

Same, ACT manifolds and cherry bomb exhaust, without the CATs. Previously running standard decat manifolds and Clive F Y piece.

Edited by angus337 on Tuesday 27th October 15:12

[angus337]

Its certainly loud when you give it some gas, but now I've fixed the injector vacuum leak, as it drives much better at low revs / higher gear in town, so is a bit more civilised than before. I also prefer the engine note with the new manifolds.

[angus337]

3rd time lucky, but finally got a working compressor tester.

The 1st Sealey kit didn't hold pressure, and the replacement maxed out at 120psi, and then failed the same as the first. Got a slightly more expensive Draper kit and this one worked fine. I've only tested the offside cylinders so far, on a partly warmed up engine, but results were good as follows:

C2 - 184 psi
C8 - 186 psi
C6 - 190 psi
C4 - 192 psi

The results are in the order I did the tests. it seems a bit odd that the pressure went up with each test, not sure if there's a reason for this, or if its just a coincidence. There was a bit of time between the tests, as its a bit fiddly to remove the plugs and fit the gauge on a hot engine and by the time I got to cylinder 6, it had cooled down quite a bit.

Anyway pretty happy that the results don't indicate any issues with C8, and will get on and tackle the other side later.