Engine going lean and stalling under boost

[clust]

I have VW Golf mk2 with totally rebuilt 1.8T AEB engine from VW Passat 1997. Engine is equipped with Garrett GT2860RS turbo and 875 cc (3 bar) Siemens-Deka injectors running with regular 98E5 fuel. Engine is running fully sequential and I'm using stock VW COP ignition coils with Megasquirt 3 v3.57 + Extra using latest stable firmware 1.4.1 and TunerStudio MS(Beta) 3.0.01 for tuning. On dyno that setup pushed out 296 bhp / 390 Nm (~17 psi boost) with stock Golf mk3 fuel pump (~80 lph @ 3 bar) but there were issues with insufficient fuel flow which caused fuel pressure to drop and engine to go lean on high RPM's so the engine was tuned to run with slightly restricted boost and advance mapping to avoid running lean. I've been running about 5000 km with that setup now and in general everything has been working fine.

To get rid of fueling problems I have installed DeatschWerks DW65V (265 lph @ 3 bar) in-tank pump and Walbro GSL392 (255 lph @ 3 bar) in-line pump on engine bay. After installations I've had stalling issues in wide open throttle conditions. If I keep 100 % throttle the engine accelerates but there will be a few quick stumble issues during acceleration, it feels like engine totally loses its power for a short period and then it returns. Regarding to AFR it seems that engine is going very lean so could it be that misfire is causing lambda to report lean AFRs or could it really be that engine is running out of fuel?

I have already checked using analog fuel pressure gauge that fuel pressure is correct (around 3 bar) at idle and it is following MAP reading as it should at least when the car is not moving. I have already ordered fuel pressure sensor to get pressure readings to Megasquirt to be able to monitor them better. Also tried to increase AE enrichment values, but it had no effect. Even tried to disable AE, no effect either. So I restored earlier AE setup which has been working with stock fuel pump setup described in first chapter. Engine is working fine on under boost conditions, no problems at all.

Attached is my current MSQ file and datalog when accelering WOT on 2nd gear from 2000 RPM to rev limiter 6800 RPM. Any help would be greatly appreciated.

[Matt Cramer]

Have you confirmed the timing is correct across the rev range?

[clust]

Ignition timing has been checked using timing lamp and timing maps are made by a professional tuner during dyno run, so I suppose that they should be generally OK. I'm using dual wheel with missing tooth setup set to tooth #1 angle 78 deg BTDC with stock 60-2 crank sensor and stock hall effect cam sensor set to "Poll level" and "Check at tooth#" to 0. I haven't noticed any sync losses either. The same setup has been working fine when I was using standard Golf mk3 fuel pump except lean AFR problems on high RPMs.

[clust]

It seems that I have solved the problem by removing Walbro GSL392 (255 lph @ 3 bar) in-line pump. The car is now running only with DeatschWerks DW65V (265 lph @ 3 bar) in-tank pump. Now I can do WOT acceleration with stable AFR 12.0 until rev limiter. Could it be that the removed Walbro GSL392 in-line pump caused cavitation which led to a situation that fuel contained air bubbles? For sure my next upcoming setup will contain decent swirl pot to get rid of these issues.

[eekoog]

Glad you solved it.
However, i didn't understand why you put two pumps inline in the same loop. Either you put a lifting pump in the tank and a high pressure pump after a swirl pot, or you keep the system you got now.
By the way, the swirl pot is useful if you experience fuel starvation wish slush in the tank. Otherwise, useless.

[benckj]

I am not a fan for using 2 in line pumps unless a surge tank is installed between. Another suggestion is looking at the fuel pump regulator as often they can be very restrictive. Not sure about the VW's and where they are located but might be worth consideration in installing a larger adjustable deg with gauge.

[WillExoIX]

Pretty sure it was the dual pumps. You put the 255lph pump AFTER the 265lph pump. So the one couldnt pump as fast as the other at high rpms. Hence WOT fuel problems.

Sent from my SCH-I535 using Tapatalk

[clust]

I thought that stock in-tank (3 bar) pump could be used along with high pressure Walbro GSL392 (255 lph @ 3 bar) inline pump but definitely I was wrong. Forgot to mention it earlier but I have already tried to run the car with Golf mk3 stock in-tank fuel pump (3 bar) and Walbro GSL392 (255 lph @ 3 bar) in-line pump on engine bay before I switched stock in-tank pump to DeatschWerks DW65V (265 lph @ 3 bar). Fuel pressure regulator is stock and it's placed on fuel rail. I have already checked using analog fuel pressure gauge that fuel pressure is correct (around 3 bar) at idle and it is following MAP reading as it should at least when the car is not moving. Anyhow, I have already ordered fuel pressure sensor to get pressure readings to Megasquirt to be able to monitor them better.

Current setup with that DeatschWerks DW65V in-tank pump alone works fine in general, but is suffering starvation issues when fuel level is below 1/3 tank. The pump is little bit bigger than original pump so I had to modify stock in-tank swirl pot assembly slighty (cut swirl pot cover open) to be able to fit it so I partly lost benefit from return line. Now I have decided to return in-tank pump back to stock model with new in-tank swirl pot to work as lift pump to feed another swirl pot which I am going to install under the car with Bosch 044 in it.

[nathanhardy]

check out holleys hydromat, i built a surge tank setup and wish i would have saw this first. its the best thing ever! it'll save you about a grand too watch the videos

[clust]

Hydramat is probably a very good product but it seems to be quite expensive as well. The biggest 30" x 14" model costs $700. Smaller and cheaper ones are also available but I think that Hydramat's area should be nearly as big as the tank bottom area is to be able to suck fuel as good as possible. Anyhow it would be nice to try how 11" x 11" ($250) or 15" x 15" ($320) model will perform. Hydramat would probably eliminate starvation issues, but another big issue in my setup is that aftermarket high flow in-tank fuel pump replacing stock pump can't be fitted inside original in-tank swirl pot without abusing it. Better fuel pump is needed as stock in-tank pump doesn't have enough flow rate. So I'll need to go with an external fuel pump anyway and decided to go with Bosch 044 fitted in external surge tank.

[nathanhardy]

Hey wanted to ask you about your check out tooth number 90 I have a VR six that I just upgraded to fully sequential fueling... I assume the settings to be the same since it's a 60-2.... what have you found work best... I seem to be having a sink loss reason number two but only at start up