Forum » General Tuning Discussion » Random misfire under a slight load.

Random misfire under a slight load.

General Tuning Discussion

Discuss all things tuning in this section. News, products, problems and results. 


Page 1
Author
411 Views

So I have a issue I cant figure out. Have a 4 cylinder vw engine when under any load it has a dead mis but at idle it dosent seem to mis as bad and the AFR is very unstable at idle and moves .5 (imperial). The tune has not changed since this started. when under load and missing the AFR is off by almost an entire point, give or take.

Here are just a few details.

-link ecu (plug and play for the Audi/VW 1.8T

-1000CC injectors

Here are the things I have done/checked.

-Swapped just ECU to another 1.8T, that car ran fine.

-Tested coils on another 1.8T, no issues.

-Logged data no issues found in the data other then my AFR is off when it engine is mis firing

-Changed fuel to fresh fuel, issue still remains

I think its a bad injector but I am not sure. Anyone else seen or have any other ideas?

So the car was running fine then this problem just developed?

Are you logging any trigger errors or scoped the trigger pattern?

If you're thinking its an injector, have you tried removing and testing?

Have you tested fuel pressure ? or tested fuel pump voltage?

If you've tested the ECU/tune on another engine and it ran fine you've definitely got a mechanical issue, start with the basics, compression and leak down test, when your pulling the plugs check for differences between the plugs.

I have done a compression check and also done a leak down.

Compression check and leak down were both fine. The engine seems solid Chris250.

Fuel pump seems to be fine and the voltage is good.

The problem just developed after a hard day at the track Chris.Wall. Not quite sure how to check for trigger errors, any incite on this?

If you press 'R' it will bring up the run time information, select the trigger tab and watch the error counter I've highlighted in the attached picture

Attached Files

Did you try changing the plugs? I always try the simplest/easiest solution first.

Once you start misfiring you cannot trust the AFR reading. It will show leaner than expected.

I'm not sure of the internal design of those engines but I once came across a 4G63 where one of the rockers came off so one cylinder had only 3 valves working. It was fine at low to med loads but would misfire at higher loads. So maybe check your valvetrain to see.

Hey Chris250.

I will check that and see what it say here in just a bit. I did pull the crank sensor and it dosent look to good. I have attached a picture.

Attached Files

That'd cause a fair few issues

so replaced the Crank sensor with and OEM sensor and issues remains. I took the new sensor back out and it look completely undamaged. I am starting to lean more towards clogged or faulty injectors. Going to send them off and have them checked since I dont have the Equipment to do this. I'll update when I have more info on the injectors.

So after some long nights of beating my head against a wall, I figured it out. I tested everything besides the injectors I knew it had to be them. I sent my injectors of to have them serviced and they found that all 4 were severely clogged. Reinstalled them tonight everything is much more stable and smooth and no mis.

Thanks for all your help guys! :)

Always good to hear of some closure on an issue