×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Problem with 5cylinder

Problem with 5cylinder

Problem with 5cylinder

(OP)
It concerns an Audi 2.3l 20v 5 cylinder. With pin coils and Bosch injectors. I have connected everything to the ECU and checked the wiring harness. All setting correct in the computer. Now the engine starts, only it runs on 4 cylinders. Cylinder 5 does not participate but the sparkplug does get wet. I made a list of what I checked.

What checked/checked/replaced

Wiring harness measured
New sparkplugs mounted
Compression measured
Fuel pressure measured 3/4bar
Mapping checked
Injector flow test done
Crankshaft signal test done
Checked firing order
Sparks from sparkplugs tested
Checked inlet valves to see if they open
Inlet gasket reassembled and additional liquid gasket used in between
Temperature sensor connected
Oil pressure sensor connected
Engine timing checked
Ignition time controlled with timing light

All sparkplugs spark when upside down. But when the sparkplug is mounted in the head, the spark is not strong enough or there is no spark at all.

RE: Problem with 5cylinder

Quote (OP)

Inlet gasket reassembled and additional liquid gasket used in between

Don't do this!

Does cylinder 5 have compression?

This is not a forum for diagnostics.

RE: Problem with 5cylinder

(OP)
Yes there is 8,5 bar compression with throttle
Closed

RE: Problem with 5cylinder

Why would you take a compression reading with the throttle closed?

RE: Problem with 5cylinder

(OP)
With throttle open the same bar at all cilinders around 8,5/9,5 bar

RE: Problem with 5cylinder

Have you tried moving the plug and coil pair to other cylinders? Does the misfire follow the pair?

RE: Problem with 5cylinder

(OP)
Yes I have tried it but the problem is than on the same cylinder as before so everytime on cilinder 5!

RE: Problem with 5cylinder

I would suspect a faulty ECU, then.

RE: Problem with 5cylinder

That or the wire to the coil pack is broken or a swage has failed in a connector. I suggest watching some South Main Auto Repair LLC videos. https://www.youtube.com/c/SouthMainAutoRepairAvoca... has terrific diagnostic walk-throughs.

RE: Problem with 5cylinder

(OP)
Yes it’s a custom ecu but the strange thing is that all the coils spark on the top of the head and in the good firing order! So I don’t know if there is something wrong with ignition or fuelinjection or something with the cilinder. But before make this new setup for the engine(wiring, coils, intake and new ecu) the engine was running good on 5 cilinders. So I think the cilinders must be good ?

RE: Problem with 5cylinder

Fuel injection sequencing?

What type is it?

Is it firing the injectors in the right order?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Problem with 5cylinder

I'm beginning to think that last cylinder is a dummy one. It has compression, spark, fuel, air, timing? Should fire.

Move the injector to another or pull the fuel supply completely and try running the engine with starter fluid into the intake to see if it runs on all cylinders. Maybe the last one is so flooded that it cannot fire.

RE: Problem with 5cylinder

(OP)
The injectors all connected to the same pins so they not sequencing. So all injectors spray at the same time before the intakevalve

I use bosch injectors number 0380155831

I already change the injectors to a working cilinder and no different. I think there is something wrong with the ignition or with the cilinder!

RE: Problem with 5cylinder

as before ... pull the fuel supply completely and try running the engine with starter fluid into the intake to see if it runs on all cylinders. Maybe the last one is so flooded that it cannot fire.

I see from another system designed by Bosch that there are usually individual transistors to control the injectors. One failure mode for transistors is to short circuit so the injector would remain on continuously. You can check for power at the injector connector. Though they may operate in tandem, the transistors are individual for minimizing power handling requirements and to allow the engine to operate if one fails. Since it is port fuel injection they are simply reproducing the function of a carburetor to supply a fuel-air mixture in the intake at the intake valve.

RE: Problem with 5cylinder

(OP)
So I have tried to let the car running with starting fluid. It really difficult to let it run and start at the same time. But the sparkplug on cilinder 5 is black so I think there is a spark but there is also fuel, the plug is wet while running with fuelinjectors. Maybe to much fuel??

RE: Problem with 5cylinder

Under the pressure of compression, the resistance of the air in the plug gap is much higher. Observing a plug spark out in the open does little to represent what goes on in the combustion chamber. Under pressure, it's possible the arc is running on the surface of the insulator.

RE: Problem with 5cylinder

Fouled sparkplug. Clean/replace.

If it fouls immediately again, you need to find out what's causing either the excess of fuel or the shortage of air in that cylinder.

An intake valve that doesn't seat/seal properly will allow some of the intake charge back out into the intake runner where it then gets mixed with even more fuel on the next intake stroke thus causing that cylinder to go rich. A little leak will make it a little rich. A big leak will make it obnoxiously rich.

Do a cylinder leak-down test.

RE: Problem with 5cylinder

It's really not wise to clean fouled plugs, The fouling burns a carbon track on the insulator that's difficult to clean off. This will lead you on a wild goose chase if you're trying to diagnose problems.

Also know that a weak ignition coil can also cause fouled plugs. I chased this problem on a dirt bike once.

RE: Problem with 5cylinder

Back in 9th grade Power Technology class the spark tester for lawnmower engines had a 1/4 inch or so spark gap to determine if there was enough voltage to fire a smaller gap at high pressures. If the spark cannot jump a 1/4 inch gap at atmospheric pressure it will not work with the spark plug installed at the higher pressure inside the engine.

Ir also looks like you have 1 of those fancy dancy spark plugs that are essentially a gimmick. Spark plugs that have a single spark gap work just as well and it is a lot easier to set the gap correctly.

RE: Problem with 5cylinder

He started with new plugs and the plug is now fouled, that suggests there was enough spark to cause combustion, but too much fuel to completely burn. Since the main change was to the wiring/electrical system, I still think the fuel injection control to that cylinder is damaged or the injector is leaking in a coincidental failure.

Since I've not heard of follow-up to check to see that the injector is getting the right pulse it's an open hole in the diagnosis.

Also open to the idea the intake valve isn't sealing but the claim is that the engine was fine before replacing things that do not affect the valves. If the valve was bent due to mistiming at some point in the assembly process it is unlikely it would seal enough to produce the measured compression.

RE: Problem with 5cylinder

Some engines come with these types of plugs from the factory now. The Japanese manufacturers seem to be favoring A standard or platinum/iridium center electrode with a pair of copper side ground straps for their more higher performance engines.

RE: Problem with 5cylinder

(OP)
Thanks for your responses, I think 3DDave may be right about using too much fuel. the plugs are new and when they turn black start with brake cleaner. there MUST be a spark. we can rule this out! we cannot rule out whether it sparks at the right time and whether the injector is working correctly. my lambda sensor indicates that the fuel correction needs to be reduced by -80 percent. too much fuel is measured in the exhaust.

RE: Problem with 5cylinder

That spark plug does not look new. It has been run for several hundred miles from the looks of the carbon inside the ceramic. Ditto on the type of spark plug to use. A single electrode is plenty.

RE: Problem with 5cylinder

(OP)
So what to do now? This is how the sparkplugs look from the running cilinders

What do you think about it? It is a new sparkplug

RE: Problem with 5cylinder

Have you checked the battery and alternator outputs? It is not unusual to have a misfire from low voltage.

RE: Problem with 5cylinder

My ol' smoky riding mower fouled plugs with carbon just like that every 4-6 hours. It would run great for a month then refuse to start, so I'd pull the plug and use a dental pick to clean it out, wire brush, reinstall, and run it another 4-6. It had a vertical crank/horizontal cylinder, snd was about as cheaply built as possible so I didn't bother trying to repair or even be upset when the connecting rod broke ~600 hours.

JMO but I suspect you have an oil control issue, maybe stem seals, rings, or bottom end damage.

RE: Problem with 5cylinder

Black like that could be bad oil control or way rich. It could be that the whole engine is on the verge of rich misfire, but the one cylinder due to inherent variations is too rich to fire under some conditions. Why it's way rich, and what to do about it, is the next challenge.

RE: Problem with 5cylinder

Probably way-rich.

Does it blow black smoke or blue? Black = rich, blue = oil. (and don't say neither - I won't believe you)

je suis charlie

RE: Problem with 5cylinder

(OP)
So I did a leak down test to check the rings. Looks good

There comes black smoke from
Exhaust

RE: Problem with 5cylinder

How is the airflow measured?

There's nothing about that in your original list of things checked.

I suspect the engine mgt system thinks there is more air flow than actually is present, hence more fuel than your engine can burn.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Problem with 5cylinder

... and which fuel injection system/controller/ECU does it use? Does it have OBDII? Is the fuel injection system/controller/ECU meant for this engine, or has it been remapped to suit this engine?

You need to find out why the fuel injection controls are commanding so much fuel to be injected, because I'm now more convinced than ever that the biggest part of the issue is that it is running obnoxiously rich.

RE: Problem with 5cylinder

LI, I was thinking something similar. Bad MAF or connection, or bad ECU.

RE: Problem with 5cylinder

So for some reason it is running way to fat. Have you checked fuel pressure? Did you check manifold vacuum? How about the engine coolant temp sensor for the ecu not the one for the gauge, is it correct resistance for the correct temperature? And same for the map, mass airflow sensor? Open up the ecu and check for leaking capacitors too, or any other water damage, when everything else checks okay then ecu huge suspect.
O2 sensors? Need a good scan tool. And like mentioned above simple things like new spark plugs, coil etc.

RE: Problem with 5cylinder

It's a new ECU - apparently the OP replaced all the sparky bits on an engine that was good enough and now it's not. It should be closing the loop on the O2 sensor in the exhaust and trimming from what it expects, not continuing to force feed.

Nothing quite as much fun as a Franken-car with a problem.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login



News


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close