Engine build progress
- Thread starter TTM
- Start date
marcoturbo
New member
Nice install. The shield looks so great [
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TTM
Well-known member
Hi Jarmo, Thanks for the feedback. At this point I want to believe it will all get solved when upgrading the fuel pump. The problem happens also when applying minimal load when cruising - let's say you drive your car at 120kph in 5th, with 0.4bar on the dash gauge, then you lightly increase load so the needle goes to 0.9bar. In that case I see the AFR jumping for about 1/4 of a second to 15-something then goes to 12 which is a more acceptable value. If it's not the fuel delivery then perhaps it's the Bosch/Vitesse stuff that can't keep up but as two mates here have had the same problem since day 1 I would rule out a faulty MAF sensor. Perhaps there is something wrong somewhere in the wiring loom but again, it would be strange to have the exact same problem on four different cars. You have this problem as well and you did the wiring on your side so the same fault done during the installation would be surprising. PS : What turbo are you running?
Fuel rail pressure should be increasing at the at the same rate as boost pressure. It sounds like the fuel rail pressure isn't increasing quickly enough. The conditions you are talking about probably represent the highes rate of change of fuel flow with the onset of boost. These conditions are most challenging to the pressure regulation system. The fuel pump is always pumping at full flow rate afaik so its not having to speed up or anything. I'd say its probably the pressure regulator or damper. Check the boost line to the regulator as a start, are they new components? Edit: Are you sure jarmo changed his, I can't see where he said that!
Hi there, Sorry I didn't mention that.. but yes.. both the damper and regulator have also been changed. I also have an adjustable FPR but the problem doesn't go away with that either. I guess one more thing to check (or rebuild) would be the wiring from TPS to DME. Could too much resistance there translate to slight delay to throttle inputs? Thom: I am currently running a Lindsey "sport" turbo. It's the one with 10cm hot side. I have bought a Garrett GT30 but it's been waiting for a right moment to install.. maybe next summer. [
] I have to say it's a little worrying to hear that you guys are also having those "weird" fueling problems. I haven't seen anyone complain at the Rennlist though.. Who knows.. maybe they all have updated their fuel pumps and that indeed is the answer! I am planning to attend a Spa trackday in June so I really want to see the problem gone before that. []
Can anyone think why it might be the pump? It can't be running out of flow rate as it goes back to the correct AFR. Maybe the lower flow rate through the fuel rail means that the pressure cant build up quick enough with the standard pump.. Edit: I guess as the boost pressure in the manifold builds up the boost pressure acts on the FPR which must close slightly to restrict fuel flow back to the tank and allow the pressure in the fuel rase to rise. The rate at which the fuel pressure rises must relate to the flow rate of the fuel pump. Maybe the flow rate of the pump needs to be higher so the fuel rail pressure rises quick enough to match the change in boost pressure.
TTM
Well-known member
While waiting for a new fuel pump to be delivered I resumed "softening the edges" on the spare intake manifold. It can be fitted with a 65mm throttle body that would need to have the same bolt pattern as the original one. The one from the BMW E28 535i seems to be a popular choice but I wondered if there were others that could do the job. Would have to work with the Bosch TPS of course. The 928 unit can be used on the original intake but at 70mm it's sadly too big for my spare intake Any suggestion?
Any suggestion?Thom I'm sure I've read others with the same symptoms as you and Jarmo. Just can't quite remember where. I'd think Rennlist. I know I see you both on there from time to time. Obviously you've spoken to John. From my dealings with him he is pretty methodical in problem solving. Seems like you need to have fuel increased on a 3-D partial throttle map. I'd do a bit more poking around on Rennlist. Maybe try Pelican too. So you both have stock intercoolers and fuel pumps? I don't know much about TPS but you would assume that it's really just measuring exactly that, "Throttle Position Switch"? So why can't the electronics be morphed onto other T-Bodies? I know where you can get a larger one that does work but they're custom and not cheap.
I wish there was a way to adjust the fuel maps in 3 D. I have only a Mafterburner and that is quite simple tool. I have tried to adjust fueling to my best knowledge but it doesn't make any difference to that lean spot. I have spoken to Vitesse about my issue and he is pretty confident it's not the software causing the symptoms. (And that makes sense as he seem to have so many satisfied customers with no problems) Anyway.. I'll try another set of injectors (this time with resistors) and will also install a new fuel pump as the current one has seen over 200000 in kilometers. I have two intakes for my car: one stock with stock t-body and the other with a flange from S2's intake. S2 throttle body is a little bigger in diameter so previous owner mixed some parts from 951 t-body into S2 t-body to make it work. I have a custom IC and custom IC piping (mine's a 968) but I haven't noticed any diffence in how the car drives with either t-body so I'll keep using the the stock one.
DivineE
New member
Could it be something to do with the moment of switch over metioned here? (extract taken from Vitesse website) "Normal batch injection with the stock DME software fires all injectors twice per cycle. Semi-batch fires the injectors once per cycle for twice as long allowing large injectors time to flow properly in low flow conditions such as idle and cruise. The Vitesse DME software automatically switches between the batch and semi-batch operation as necessary while the engine is running"
TTM
Well-known member
Jarmo, Would be interested to see a picture of your non-stock intake. My spare one has a big plenum so am feeling concerned using a stock throttle body may significantly hinder performance. Ben, I have stopped thinking on this issue, will just see how it works with an upgraded fuel pump.
That is weird. It actually reminds me very much of something I was getting a few years ago. Get on throttle and for an instant it was like the whole car shut down, then it would carry on normally. I never found out what it was either Thom. A seized motor or two (I can't remember) and when we came back it wasn't there. I actually have a dyno chart too. Looks like the flight path of a Bumble Bee on LSD. Have you posted this example on Rennlist? I would as you have so many more VR customers over there.
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