1.6k - strange intermittent 'sucking' noise

[neil wattam]

hi all,

A reach out to the K experts in particular - my 1.6k has developed a sucking noise that's most noticeable when idling or not under load - it sounds like your sucking air in through your teeth. It is not a regular rhythm but does keep doing it and is in very short, sharp duration.

I've taken a video but don't think I can upload them here? Can share via whatsapp etc if someone would be willing to take a look...

It's running Rover throttle bodies btw and the noise appears to be coming from the inlet side of the engine. 

Appreciate thoughts!

[Wrightpayne]

Neil,

Is it dry sumped? The DS pump can cause funny noises to occur.

Ian

[revilla]

Neil WhatsApp'd the video to me. I've upload it to YouTube here:

Is sounds like an irregular knocking / tapping noise to me on the video but Neil assures me that in real life it sounds like short bursts of sucking.

The dry sump scavenge pump was my first though too but it doesn't have one! Just Apollo.

Neil is going to pop over to see me tomorrow if we haven't come up with something before then. Anyone got any further ideas?

[revilla]

Actually I did once hear an engine making a sound very much like that, and some fool had left the cam belt tensioner loose (... err ... guilty as charged)!

 

It did make an irregular chink-chink sound that could have been mistaken for bursts of sucking. Neil, definitely worth a quick check before running the engine much more. One a VVC engine I think there are 5 small (8mm head) bolts around the top of the cover to remove and one (10mm head) down at the bottom that you just need to slacken. You will see the belt runs around a tensioner pulley on the left. That shouldn't be loose.

[revilla]

Had a look at the car this lunchtime.

It's spitting back into No 3 inlet at idle. As soon as you raise it slightly off idle, No 1 joins in big time, popping and clattering through the trumpet. If you hold your hand in front of the trumpets you can feel the kick, and you can feel it through the throttle too as the butterflies are being kicked 

Neil has left the car with me. I'll check the cam timing when it cools down but I don't think it's far enough to do that. The car has Verniers and all the timing marks align so nothing has slipped (it started doing this suddenly), but only a proper check will prove that the Verniers are set up correctly. It actually idles quite nicely so I don't think it's a million miles out.

Failing a cam timing error I reckon it must be sticking or damaged inlet valves?

Anyone else got any ideas?

[21jigsaw]

Sounds like the induction stroke on the inlet manifold sucking on the throttle  flaps shut. try slight adjustment and see if it changes .

[7 wonders of the world]

I've seen a couple where during cam belt change and retiming on verniers the cams have kicked back and have resulted in a very very slight bent inlet.

Both idled well and compression tests even showed very good results - leak down showed it clearly though.

1 in particular had a light tapping noise on idle once warm sounded like a slack valve clearence, (these were a thou loose) it was actually the edge of the valve tapping the head

Both were running REC wasted stem valves, 

[revilla]

@Dave, it's definitely blowing rather than sucking in. If you hold your hand close to the trumpets you feel a warm kick away from the trumpet.

@Neil, thanks for the info. It's definitely a possibility. I've got the car at mine for a while, so if the cam timing check shows nothing I'll give it a leak-down test next.

[21jigsaw]

Andrew,

The noise disappears when the throttle is opened ? Is the noise coming from all the tracts? Does frequency / volume change when you remove the vacuum hose on the offending inlet tract?

Dave

[revilla]

Dave,

 

At idle it's only really No 3 doing it, however if you open the throttles a bit No 1 really pops and bangs through the trumpet. It's not just a bit of a tapping sucking noise at that point, at light throttle but off idle it's really properly backfiring into No 1 TB. It's kind of like exhaust overrun popping and banging but coming straight out of No 1 trumpet. I'll have to see what happens when removing the vacuum line.

 

Andrew

[SLR No.77]

Andrew, what happens if you swap the injectors around, e.g. 1&2, 3&4?

Stu.

[revilla]

Stu, another thing to try, thanks.

[oilyhands]

Sneezing like that can also be caused by lean fuelling or the ignition timing hopelessly retarded, both result in incomplete / slow combustion so the the charge is still burning/expanding when the inlet valve opens. 

Oily

[revilla]

Thanks Dave. Under either of those conditions would you expect the driving of the car to be badly affected? If the timing were so far retarded that that it was still burning as the inlet valve opened, would you expect some popping in the exhaust as the exhaust valve will also have opened long before that point? The exhaust sounds perfectly smooth and normal and the idles nicely and generally drives OK.

[7 wonders of the world]

Luckily you know a man who can interrogate MEMS and look at the ignition map  

Worth also have a spray around the manifold etc with a can of carb cleaner to pick up any air leaks, particularly on the TB spindles.

May of missed this in the thread trail..... but has this fault just started...?

or has work been carried out else where...?

if's its a long term fault then also consider the butterflies may requiring resetting in the bores often made worse by worn spindles or bushings. which can be masked by using bypass balance screws to give a good idle.

[oilyhands]

Normally the sneezing is most noticeable on the induction side. Popping from the exhaust is unburnt fuel igniting well along the exhaust, a little of the flame front exiting the exhaust valve is normal.

Oily

[neil wattam]

Thanks guys for your input and Andrew for his work and help so far!!

7wonders.... it has only become an issue in the last 2 weeks or so and I've not touched it mechanically. The only mechanical tweaks of late were fitment of new clutch and throttle cables, and I believe a tweak to the lamda sensor which wasn't attached correctly / very well. These fixes were done at Nick Potters and I trust them to have done a good job on those specific bits and merely a coincidence of close timing. 

[neil wattam]

And I assume it makes no difference, but for completeness (for others) it is running 285 cams, vernier pullies, emerald ecu and a power speed 4-2-1 exhaust. I'm not aware of any Other mods 

[revilla]

Investigations so far this morning:

Warmed it up. Took this video of it running. It was really unhappy if you tried to hold it just off idle, popping and banging aggressively into the throttle bodies. Actually found that 3 out of 4 cylinders are doing it, 1 isn't. You can clearly see bright rings of fire around the throttle butterflies. 

.

When it was fully hot I did a leak-down test. Tested each cylinder three times, using 80psi at TDC and a sensibly calibrated (home made) leak down tester that I trust, turning the engine through three complete cycles, just in case were sealing intermittently. Results were very consistent:

No 1: 78/80
No 2: 78/80
No 3: 76/80
No 4: 80/80

So a little down on No 3 with about 5% leakage but nothing too bad, and I would say that about 25% of that leakage was inlet valve, the rest ring seal, so really nothing that could obviously be causing this.

Then checked ignition timing. I checked ACTUAL timing by cross-checking the ignition waveform against the crank sensor waveform on a scope, rather than MAPPED timing (which I'll look at later just to compare).

At idle it was jumping around a bit as the ECU tried to stabilise the idle, but was typically around 5° ATDC:

Holding a steady-ish 3850rpm it had advanced to around 52° BTDC. It was still popping and banging furiously through the trumpets, so I don't think it's down to being hopelessly retarded:

Ignition primary voltage waveforms were mostly normal, with about 1ms spark burn time:

There were quite a lot of misfires like this:

But again that's not unusual to see at idle. It seemed to clean up when revving a bit. I took the spark plugs out and they were very oily, but I'm fairly sure it was just external leaks (cam cover gasket looks shot!) and the electrodes were not contaminated. I swapped in a set of brand new double-platinum NLP100290s and it made no difference at all.

I will have a look at injectors later, but 3 out of 4 were doing this so unlikely to be an injector fault, suppose it could be something wrong with the injector drive - it did smell a  bit rich as I was warming it up and the plugs were a little dark, but not massively so.

I'm still struggling to what could be regularly igniting the charge in the inlet runners other than intermittent valve seal issues allowing it to spit back, even though the leak-down didn't show anything statically.

Whatever it is, it's really not very happy at all. When revving it, and just after starting, it doesn't sound like it is firing evenly across all the cylinders.

[oilyhands]

Trim the fuelling at idle and see what transpires. Check the TPS to ensure it is reading correctly, if it misreports throttle position it will be lean on transients.

Oily

[SLR No.77]

Is the FPR okay? Have you measured the fuel pressure?

Stu.

[revilla]

Haven't had a chance yet, but as this has a sudden onset across multiple cylinders are likely to be something common like that, so it's on the list thanks.

[revilla]

As is a quick look at the injector drive, I've seen a poor ECU earth leave injectors "sluggish" to open leading to lean mixture before, but there usually more sign of trouble on the ignition waveform where the "ground" voltage ramps up with the current but it looks clean.

[Wrightpayne]

Have you checked the cam timing ? Is it possible one of the verniers has slipped its 'timed' position?

Also, Neil talks of a lambda issue while in for service - has this been explored (in the absence of any other recent changes)?

Ian

[revilla]

I've done a quick "rough check" on the cams, as in all the timing marks align correctly (so doesn't look like the belt has slipped) and the Vernier bolts are tight with no witness marks to suggest they've recently moved. Of I don't find any other cause first I'll get the timing gauges on it when I get a chance. And no haven't checked out the lambda sensor yet, if a lean mixture really is enough to make it ignite in the inlets then I guess it could be that simple. I need to get the Emerald software and a cable set up. Can anyone confirm whether the Emerald software is happy with a USB virtual serial port cable? My laptop doesn't have a built-in COM port.