AAN buggy engine overboosting/backfiring

[Alastair]

I suppose i better point out at this time that it's I that's owns and built this Buggy, with much help from my good friend Stev in all the previous correspondence. We both are quite keen to have with everyones help, have any outstanding issues resolved as this project is a labour of love, not to mention the power - weight it can't deliver with the right tweaks, and of corse the 5 cylinder sound that this engine can produce!
We will post some footage of it soon, as and when we resolve some of the teething problems.
The Turbo is T3 Turbine and T4 Compressor.

[prj]

I agree, with regards to frp. Instead of fuel pressure increasing as the boost rises it actually decreases. That must be leaning out the Fuel Injectors at full boost.

You have 6 bar of pressure at idle. That's silly.
This variation of Motronic can not compensate for fuel pressure. If you mess with fuel pressure your entire map will be wrong and your fuel mixture will be wrong.
And yes, at boost you should be seeing 5 bar, not 4 bar.

The vacuum/Pressure side of the Adj Fuel Reg mustn't be doing the job properly or the Fuel Pump can't withstand the high boost and flow.

If you have one of the china FPR's then get rid of it and fit OEM! I have seen issues with them so many times now...
The fuel pump should easily withstand 400hp and up. It has no issue delivering fuel on my car with more boost than you are running.

As for a T3/T4 turbo - you need to upgrade your injectors if you want to make use of it. Stock injectors max out if you boost more than 1 bar at 6500+ rpm.

[S2central.net]

I supplied a generic ECU upgrade for this buggy... the turbo was not well enough described to me to try anything else - it was designed to run with factory WG configuration, 4bar fuel rail, stock WG spring and stock injectors. If anyone arses around with those things - then it aint gonna run right.

Pity nobody came to ask me / email me first about any running issues.

[newsh]

Sounds like the FPR is not connected to the Inlet manifold..

[prj]

Sounds like the FPR is not connected to the Inlet manifold..

LOL
Yeah I just thought of that... you are right. Absolutely. And it's set at 6 bar and they are running 2 bar boost.... on stock injectors...

Boom very soon.

[S2central.net]

@Alistair...

Sounds like I need to come over and eyeball this engine on wheels to see you have it configured to run right at all. Then we can talk about your desire for silly boost levels and I figure what injectors are needed to get you there.

Give me a shout at S2central@mac.com or send a PM

[Stefen]

It just came to me when I woke up this morning why the FPR is running so high. Recently we upgraded to the fuel pump which was mentioned, and the FPR has not been adjusted for it. That doesn't explain why the pressure drops as the boost increases. The connection to the plenum has been checked.

I should mention why the 3 party FPR is there in the first instance - We weren't 100% sure if the fuel pump was up to the job, so we were keen to gain insight into the fuel pressure. In hindsight it may have been best to simply install a gauge, but at the time an adjustable FPR with gauge was available quite cheaply, so that path was chosen. The stock pressure level was looked up and the FPR was set to the same level. This needs redone for the higher flow rate of the new pump.

At the time the chip was upgraded, the injectors were stock as was the fuel rail & FPR. The wastegate was as shown in the pictures at the time and it was to be set at 0.5 Bar. We were very pleased to have the immobiliser bypassed and see the engine going at last. The build was on going, so our attention was tuned to the many many other things which needed made, fitted and tweaked. As the buggy progressed our attention gradually turned back to the the engine. The plugs, timing belt, pulley etc. were changed, the N75 was added etc. but two issues seemed to be present - banging over 1 Bar & the boost control wasn't always limitiing at 1.5 Bar and only once did it go down to 1 Bar at the limiter (in about 20 runs).

Nowadays people turn to the forums for help, and given that I won't think the software was as fault (CS background) we thought is was a hardware related issue, the fourms seemed to be a great place to get a few ideas. It's also good in that one idea sparks another, and it puts the thoughts and facts on a readable format so we can review them later. A very useful process overall and a good way to learn and crystallize thoughts.

When the wastegate bolt is loosened, the lowest it will work at is 0.4 Bar (BTW All these boost measurements are taken from the plenum. The feed for the N75 is taken from the compressor housing.) I'm wondering about replacing the WG spring with a weaker one.

With regards to the banging I guess we need to swap good coils POSs in and out.

@Paul - Certianly you are very welcome to call around and see if these issues can be sorted out. Cheers.

[S2central.net]

http://www.adelekirby.com/wp-content/uploads/2011/01/DoubleFacePalm.jpg

Do NOT mess around with FPR !

The only reason to upgrade a fuel pump is if it cannot supply enough fuel for the demands of the engine.

- You MUST keep FPR at 4bar
- You MUST keep FPR connected to IM / plenum

The max fuel pump flow you currently need is approx 1.8 liters / minute with a pressure of 5.5bar (4bar rail + 1.5bar max boost). The stock S2/S4 fuel pump is well capable of that, and lots more actually.

[prj]

It just came to me when I woke up this morning why the FPR is running so high. Recently we upgraded to the fuel pump which was mentioned, and the FPR has not been adjusted for it. That doesn't explain why the pressure drops as the boost increases. The connection to the plenum has been checked.

Then your FPR is not working properly.
You do not have to adjust an FPR when changing the pump. You don't have to touch that at all.

I should mention why the 3 party FPR is there in the first instance - We weren't 100% sure if the fuel pump was up to the job, so we were keen to gain insight into the fuel pressure. In hindsight it may have been best to simply install a gauge, but at the time an adjustable FPR with gauge was available quite cheaply, so that path was chosen. The stock pressure level was looked up and the FPR was set to the same level. This needs redone for the higher flow rate of the new pump.

Quite cheaply huh. So replacing engines is cheap now? Because this is what you will be doing when you use most cheap adjustable FPR's.

At the time the chip was upgraded, the injectors were stock as was the fuel rail & FPR. The wastegate was as shown in the pictures at the time and it was to be set at 0.5 Bar. We were very pleased to have the immobiliser bypassed and see the engine going at last. The build was on going, so our attention was tuned to the many many other things which needed made, fitted and tweaked. As the buggy progressed our attention gradually turned back to the the engine. The plugs, timing belt, pulley etc. were changed, the N75 was added etc. but two issues seemed to be present - banging over 1 Bar & the boost control wasn't always limitiing at 1.5 Bar and only once did it go down to 1 Bar at the limiter (in about 20 runs).

Your wastegate boost is still too high. If you adjust it to stock level (0.35-0.4 bar) then your boost problem will go away. The banging is likely because of crazy overfuelling due to either faulty or incorrectly connected FPR! The coils and POS are probably fine. The reason the fuel does not ignite is due to an excessively rich mixture - I did not know that when I told you to check plugs/coils/pos.

Nowadays people turn to the forums for help, and given that I won't think the software was as fault (CS background) we thought is was a hardware related issue, the fourms seemed to be a great place to get a few ideas. It's also good in that one idea sparks another, and it puts the thoughts and facts on a readable format so we can review them later. A very useful process overall and a good way to learn and crystallize thoughts.

The software is not at fault - but Paul knows a thing or two about hardware as well.

When the wastegate bolt is loosened, the lowest it will work at is 0.4 Bar (BTW All these boost measurements are taken from the plenum. The feed for the N75 is taken from the compressor housing.) I'm wondering about replacing the WG spring with a weaker one.

WG spring should be stock.

With regards to the banging I guess we need to swap good coils POSs in and out.

No, you need to sort the fuel pressure first! Do not even start the engine until you have sorted the fuel pressure.
You will foul your spark plugs and the banging can crack your manifold.

Throw away the cheap FPR, fit STOCK AAN 4 bar FPR.
The fuel pump is good enough to run setups up to 450hp. It will deliver solid fuel pressure with stock injectors even at 100% IDC.

Put everything to stock. Stop screwing with the wastegate and the FPR without understanding what these things do or how the engine works internally.
That will be the fastest way to get your buggy running well.

[S2central.net]

Also - do not mess with that WG... I will check the N75 plumbing and do an overall diagnostic check on sensors etc if you like

Might be able to get over next weekend sometime - send me a PM to setup.

Paul

[Stefen]

That's me told! It's clear what needs done. I'll talk to Alastair later on and see about chopping that FPR off and is he free this Saturday. Thanks.

[Stefen]

For reference, here is a picture of the WG earlier in the build. The banjo fitting around the adjustment bolt is no longer there.

[S2central.net]

I hope that WG has a port on the lower chamber more importantly... thats what needs to plumb into WGFV / N75.

[Stefen]

Just a quick post - will write more tomorrow:

1) The 3rd party FPR was faulty. The Audi one was put back on along with a gauge and behaved perfectly.

2) The N75 was faulty. It leaks too much. This was swapped for one out of the TT and the boost now is limited to 1.5 Bar and tails off to 1 Bar at high revs.

3) There were a couple of boost leaks that were fixed but made no difference.

So, too much air and too little fuel was getting in, on account of the faulty FPR and N75.

We are so pleased that it is running well! Thanks to everyone that helped. There are still a few things to sort out, but that is the last big problem sorted! Stay tuned!

[newsh]

Nice one, so the N75 was leaking causing the wastegate to not open fully.