Hi all - sorry to resurrect an ancient thread, but I tripped over it when doing a Google search for "injector pulse duration" - From reading though this thread, I reckon you may be able to help.....
I run a Fiat Coupe 20v turbo. Not a million miles removed from the Audi 5-pots I guess - certainly sound very similar and a few of us on the Coupe forum (www.fccuk.org/forum) are getting very decent bhp (500+)
I've recently had a pretty big rebuild after wearing my oil control rings - I took the opportunity to have forged pistons, flowed head etc. With a fairly hefty turbo (GT2871R) I'm now pulling 395bhp and 330 lb-ft of torque. However, to get this, I junked the 330cc injectors and fitted 384cc jobbies from the 16v turbo Coupe (same as the Integrale)
The car now runs great at the top end, as the headline power would suggest, but the low-end running is awful. An ECU reset cures it for a day, but then the ECU "learns" the overfuelling and cuts it back, resulting in it going lean.
Thats problem 1
Problem 2 is that the car is very on/off at VERY light throttle openings - its either accelerating or decelerating - won't hold steady. The throttle position sensor is reading fine (I have a Sykes-Pickavant code reader, so I can check) The TPS voltage is fine. The MAF voltage is fine, but the lambda voltage is dropping as far as 0.03v - I assume due to the fuel being cut completely when the ECU senses there's too much being injected.
My theory is that one or more of the following is happening
1) The minimum pulse duration of the standard injectors is the same as the new (larger) ones, meaning that when the ECU says "give me the minimum", it gets 20% more than it expected, causing overfuelling, which gives a little acceleration, then it cuts it straight back again.
2) I read earlier in this thread about TPS / MAF plausibility checks - is it possible that something is incorrect there - not sure it can be though, as the engine is still 2 litres, so its not using any more air when off boost (its using LOTS more on-boost - I run 1.6 bar
)
I also run a Unichip over the stock ECU with a modded chip (raised fuelling, no fuel cut at 1.5 bar and 200rpm extra on the rev limiter). The Unichip is mapped against a base map in the ECU, and other than this horrible on/off lark, when the ECU has been freshly reset, it goes like stink and has decent throttle response, etc. However, the ECU learns quickly - 50 miles later and I've got fluffy throttle, pinking and general misbehaving.
Anyway, I'm rambling - my question. Does anyone amongst the obvious experts on here know if injectors have minimum pulse durations, and if so, how the hell do I overcome the overfuelling problem caused by bigger injectors firing for the minimum period
thanks in advance
Nigel
I run a Fiat Coupe 20v turbo. Not a million miles removed from the Audi 5-pots I guess - certainly sound very similar and a few of us on the Coupe forum (www.fccuk.org/forum) are getting very decent bhp (500+)
I've recently had a pretty big rebuild after wearing my oil control rings - I took the opportunity to have forged pistons, flowed head etc. With a fairly hefty turbo (GT2871R) I'm now pulling 395bhp and 330 lb-ft of torque. However, to get this, I junked the 330cc injectors and fitted 384cc jobbies from the 16v turbo Coupe (same as the Integrale)
The car now runs great at the top end, as the headline power would suggest, but the low-end running is awful. An ECU reset cures it for a day, but then the ECU "learns" the overfuelling and cuts it back, resulting in it going lean.
Thats problem 1
Problem 2 is that the car is very on/off at VERY light throttle openings - its either accelerating or decelerating - won't hold steady. The throttle position sensor is reading fine (I have a Sykes-Pickavant code reader, so I can check) The TPS voltage is fine. The MAF voltage is fine, but the lambda voltage is dropping as far as 0.03v - I assume due to the fuel being cut completely when the ECU senses there's too much being injected.
My theory is that one or more of the following is happening
1) The minimum pulse duration of the standard injectors is the same as the new (larger) ones, meaning that when the ECU says "give me the minimum", it gets 20% more than it expected, causing overfuelling, which gives a little acceleration, then it cuts it straight back again.
2) I read earlier in this thread about TPS / MAF plausibility checks - is it possible that something is incorrect there - not sure it can be though, as the engine is still 2 litres, so its not using any more air when off boost (its using LOTS more on-boost - I run 1.6 bar
)I also run a Unichip over the stock ECU with a modded chip (raised fuelling, no fuel cut at 1.5 bar and 200rpm extra on the rev limiter). The Unichip is mapped against a base map in the ECU, and other than this horrible on/off lark, when the ECU has been freshly reset, it goes like stink and has decent throttle response, etc. However, the ECU learns quickly - 50 miles later and I've got fluffy throttle, pinking and general misbehaving.
Anyway, I'm rambling - my question. Does anyone amongst the obvious experts on here know if injectors have minimum pulse durations, and if so, how the hell do I overcome the overfuelling problem caused by bigger injectors firing for the minimum period
thanks in advance
Nigel
)
Comment