bogging/missing until you lift off throttle and go back on it

[grungeisdead]

Helloooo!

For those who don't know, I have a Mk1 Golf with a G40 Engine fitted, it also has a T25 Garret with a GT cam and the 6 psi boost switch mod.

The engine has ran sweet as a nut since I finished building it in November last year, my only gripe was max boost was 0.5 psi but I was never too fussed about it until I had replaced my fuel pumps.

I did some welding on the car a couple of months back, and had disconnected the battery while doing so, to avoid shorting any of the electrics, however ever since then I have been having running issues.

Basically, you would be driving along and start accelerating, the car would bog down like hitting a brick wall, with any amount of throttle pressure and this is only rectified by lifting my foot entirely off the throttle and then back on and it would go like shit off a shovel.

It's beginning to get more and more frustrating in daily driving and is taking its toll on already tired engine mounts with the constant accelerate, lift off, accelerate.

In my quest to solve it, ive done the following

New Inline Fuel Pump
New In Tank Fuel Pump
New Fuel Pump Relay
Cleaned Spark Plugs and set gap to 0.7mm (Tried both W5DP0's and NGK BP7EVX)
New Rotor Arm
New Dizzy Cap
New Spark Leads
Known working coil
New Coil
New Blue Temp Sender
Known working lambda
New Lambda
Replaced all engine earths and cleaned mounting points
Replaced all vacuum hoses
 Of which have the following setup
  2 brake servo take offs, one directly to FPR, one directly to ECU - ECU one is 470mm
  Bottom of inlet manifold take-off has the following connected - dump valve, actuator, 6 psi boost switch and boost guage
Set the static timing using a screwdriver to note TDC and marked up the crank pulley and casing
Set timing to 6 deg at 2k rpm in service mode (was set to 10 deg)
Set CO to 0.7% in service mode using a gas analyser
Changed the actuator - which has finally given me a bar of boost (gave me 2 bar with a bleed valve - standalone from the rest of the vac system, plumbed into the main system now to avoid dangerous boost spikes)
Upgraded the coil to a 8v digifant GTI coil and amp

The CO will now only go down to 4.3% in service mode for some reason, and no amount of tweaking the CO changes it, this happened to my last CO pot, so replaced for another and its done it again)

The engine is running very rich, pretty much shows rich on the narrowband AFM all the time, apart when its bogging down, where when warm it reads in the middle)

Today when I was performing the 8v coil mod, I decided to check the ECU pinout to trace the black/green wire and noticed that inside the ecu connector plug was a load of water and some green furry connections! Its a wonder the car ever ran at all, So i stripped the ECU down, no water inside thankfully, and cleaned up all the connections and put it back together.

Driven home tonight and still got the same behaviour - driving along, car starts bogging down under any acceleration, lift off the throttle and back on it again and the car is happy again. also possibly worth noting that if you try and drive off with very light throttle the engine will try and cut out, so a bit more throttle and its sweet. It also backfires and pops on overrun. starts up and idles fine until warm where it occasioanly wants to drop the idle and sometimes cut out.

At the end of my wits now and have considered swapping it all out for my mapped G-lader setup, but it involves making a custom drivers mount, which I plain cant be arsed as I dont have a spare engine, so it would be an all or nothing affair.

Has anyone else experienced issues like this?

Things I have left to consider
 Fit my wideband lambda - VEMS with datalogging - got my boss just need to fit an appropriate holesaw to drill out a hole in the exhaust, or take it to an exhaust place to do on the ramp
 Check resistance and connectivity between the ecu pins and relevant sensors/ground
 Check Pressure Switch calibration and wiring
 Replacement MAP sensor
 Replacement ECU
 Put the G-lader stuff on


Help mehhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh!

[xandyx]

i'm having the same problem on a stock g40, i allready replaced the same as you did.

i'm starting to lose my mind arround this problem.. on mine, when i lift the throttle and put it down, it goes ok for 1 or 2 miles, then, it starts to bog again..

let me know if you find something!!

cheers

[Andy]

Check the harness connections and try a different ECU.

[ereeiz]

I've got a couple of ECU's (std and one with an SNS5 in) if you need to borrow one to check gimme a PM.

[grungeisdead]

Cheers dude, I have a spare ECU in the post (forgot to pick it up when i picked up a spare engine) and a spare loom at the unit. I also have another ECU but its fitted with a 250kpa map sensor so no use without an appropriate map.

If I need it i'll give you a shout! need to catch up with your bro anyway been too long!

[grungeisdead]

Connected up my wideband last night.


get around
10.1 -> 11 on start-up
14.7 -> 15.0 on partial throttle (about -0.3 bar on guage)
12 on boost
11.3 on full boost
19.5 on over-run/no throttle in gear

when it does start missing/bogging down the AFR values spiral upwards into mega lean.

Does this sound correct? CO Pot used at idle, lambda used at partial throttle, MAP used when WOT switch (in my case 6 psi switch is activated)

[Yoof]

Too rich on boost, and that's fairly rich on cold start too.

It sounds like you'v never had the engine running full boost on this setup?

What's the map from?

[grungeisdead]

Since last week is the first time I've ever had the engine pushing out over 0.5 bar boost, by changing the actuator. It's a new standard one, but as I now know the original actuator was at fault, I can splash out on a forge one now, happy in the knowledge.

the map history is unknown, it has turbo written on the chip, but the previous owner has very little history on the engine, unsure if he bought the chip seperately, or bought it as part of an engine conversion for his Mk2 olop.

I do want to get the car mapped, however I'm unsure if everything is healthy enough on the car, for the mapping session to be worthwhile. If I do get it mapped, i'll stick the 250kpa MAP sensor on along with some G60 injectors.

What is the potential problems that may be encounted by running the ECU with the 250kpa MAP sensor temporarily. will it just simply run like poo in comparion. I dont know enough about the sensors to even hazard a guess.

Can the map sensor be tested with a multimeter and some way of regulating pressure to the system with say a foot pump connected to the ecu vac take off?

[Yoof]

250kPa sensor on a 200kPa map won't run.

I'd start with a known good map (that's actually for the spec you're running) and you know is for the 6psi boost switch.

You're pissing in the wind with some random chip.

[Robin]

hall sender issue?

[Etches]

Bumping an old thread here buts its a similar situation with my ppp map being very rich (only bogs on part throttle)
Cold start afr 10.3
Warm idle      15
Boost.            10-11
15% throttle   10-11
20-30% throttle 13-15
Over run 17- off the scale

Map is for my exact set up 1341 15psi, with 6psi switch. Got brand new bosh lambda and working blue temp

[grungeisdead]

I never sorted this, started driving it again last month, spent a day troubleshooting but still couldnt get to the root cause, so ripped the engine out and stuck a G setup on it, whilst I muster up enough energy to look at this another time!

[Andy]

Bumping an old thread here buts its a similar situation with my ppp map being very rich (only bogs on part throttle)
Cold start afr 10.3
Warm idle      15
Boost.            10-11
15% throttle   10-11
20-30% throttle 13-15
Over run 17- off the scale

Map is for my exact set up 1341 15psi, with 6psi switch. Got brand new bosh lambda and working blue temp

Very light throttle application is too rich, other AFRs are okay for a generic chip. Is it light throttle no boost, or light throttle on boost that's doing it?

[Etches]

I think its the boost Andy, switch is defo at 6psi too. Won't be long till I'm changing the chip to the red injector one , still need to Pm you about it Andy. ALthough I don't wan't to push you whilst the baby is due!

[Andy]

If it's doing it on boost, it might be because you're running it at a lower boost level than the chip was mapped for. It's not dangerous, but obviously impacts driveability.

The chip's done for 15psi, which means that some map points are only passed-through briefly on a transient event, but end up having lots of fuel in to ensure the full boost/throttle fuelling remains spot on during spool-up. Now if you're running say 8psi, then the 'pass-through' map point might be used more frequently and for longer - and as you're on a lower boost it'll need less fuel.

I'd try and drive around it if you can for now, and then once the motor has a few more miles on it I'd wind the boost up and hopefully you'll find all is well.

Won't be doing any mapping for the next month or two, currently uber-busy getting ready for baby and trying to get my own Polo sorted in time. Once we've got sorted after the new arrival pops out; I'll try and post up a few mapping dates for people.