Self tuning T5

[Rodders]

Hi Guys

Well being fairly new to the forum one of my first questions when I joined, was how much boost should a healthy T5 pull on the Volvo standard boost gauge.

Well, my car a 1995 855 T5 appears to have taken matters into its own hands with regards to tuning and boost. Now when I boot-it, I can get the needle off the end of the boost gauge by a good 2mm or so. The car goes like a rocket. However while this is great fun and may have saved me a trip to Volvo Tuning, I can't help feeling all is not well. If I push too hard the engine seems to make a thump and die...is this "overboost" mentioned elsewhere.

Any ideas what can cause this very sudden gain in boost pressure please...maybe the BHP fairy visited one night while I was asleep!!!

Thanks in advance

Rodders

[Babybadger]

Hi Guys

Well being fairly new to the forum one of my first questions when I joined, was how much boost should a healthy T5 pull on the Volvo standard boost gauge.

Well, my car a 1995 855 T5 appears to have taken matters into its own hands with regards to tuning and boost. Now when I boot-it, I can get the needle off the end of the boost gauge by a good 2mm or so. The car goes like a rocket. However while this is great fun and may have saved me a trip to Volvo Tuning, I can't help feeling all is not well. If I push too hard the engine seems to make a thump and die...is this "overboost" mentioned elsewhere.

Any ideas what can cause this very sudden gain in boost pressure please...maybe the BHP fairy visited one night while I was asleep!!!

Thanks in advance

Rodders

Sounds like the BCS (boost control solenoid) is doing weird things......sure you haven't dropped a new ECU in it? I would pull the codes from it and at best get to Volvotuning and let them look at it.......where are you based?

[arbee]

lol - i really dont think it should be going off the scale! - surely can only be the BCS?

[Justin]

Also maybe the vac hose has come off/split to the actuator, same result :)

[T5ER]

Does not sound good at all.I would refrain from giving it to much of the go go pedal for now or you may be picking some internal engine parts up off the road

[blackbooty]

Also maybe the vac hose has come off/split to the actuator, same result :)

very true.

bcs, or as justin wrote.
ive hit overboost 50 times + on both my 5's, theres lots of scare stories about bending rods, but as hard as i tried... i couldnt do it to my doner T5
(not joking) i even took the actuator out of the equasion so that the wastegate could not open ! and yes... it still purrs.

volvo and everyone else that earns money from unwell volvos will tell you its of utmost importance to get it sorted yesterday, just remember this...
your hitting a protection system developed and installed by volvo to protect the engine in case of componant malfunction.

just be carefull of giving it a bootfull from standstill.

wayne

[volvotuning]

Hi Guys

Well being fairly new to the forum one of my first questions when I joined, was how much boost should a healthy T5 pull on the Volvo standard boost gauge.

Well, my car a 1995 855 T5 appears to have taken matters into its own hands with regards to tuning and boost. Now when I boot-it, I can get the needle off the end of the boost gauge by a good 2mm or so. The car goes like a rocket. However while this is great fun and may have saved me a trip to Volvo Tuning, I can't help feeling all is not well. If I push too hard the engine seems to make a thump and die...is this "overboost" mentioned elsewhere.

Any ideas what can cause this very sudden gain in boost pressure please...maybe the BHP fairy visited one night while I was asleep!!!

Thanks in advance

Rodders

Sounds like a split in one of the BCS pipes. That thump you feel is indeed the overboost detection and fuel cut. It's explained in detail here (ignore the advert about the new ecu upgrade, just read on to the bottom of the page about 850 T5 overboost) -

http://www.vpcuk.org/forums/t12400-fao-diy-tuners.html

Adam.

[zanelli15]

After reading the information about over boosting to which i found interesting.

I was wondering then if the boost is increased to say 12 Psi and does not cause overboost, which i believe should cut in at 14.7 psi ( 1 bar) (my car is set to 10PSI)

Then if overboost is only detected by the mass air flow into the engine more if boost is increased which is logical. Then does this also mean that if boost is increased to the above amount say using a MBC then the air flow ratios will be adjusted to suit since it will be still running within the calibrated amounts the standard ecu is programmed to work out.

If however it goes above the 14.7 psi and overboost cuts in then what we are saying is that the standard ecu can no longer calculate the correct amount of fuel that is required for that pressure and therefore the amount of air that is required by the engine?????? to get the correct air - fuel ratio.

This may not make any sense at all. at work so having to rush what i write.

My car has also had its cam timing altered to give more lower end power, makes a hell of a differance but affects top end power, which does not bother me I want acceleration not top speed.

[volvotuning]

If however it goes above the 14.7 psi and overboost cuts in then what we are saying is that the standard ecu can no longer calculate the correct amount of fuel that is required for that pressure and therefore the amount of air that is required by the engine?????? to get the correct air - fuel ratio.



It's just a limit set in the ECU to stop overboosting.

AFR is totally seperate and is not maintained by closed loop fueling at full throttle.

Adam.

[Rodders]

Guys

Thanks for all your input into this, having had a look underneath at the weekend the 'red' hose from the turbo to the bcs had split just where it joins the turbo so difficult to see from above...hose now replaced and all back to normal...but it was fun while it lasted though while it lasted is probably a good express for the con rod!!!

Thanks again guys

Good advice

Best

Rodders