When starting car, I heard loud pop, intake manifold comes disconnected from motor
07-24-2017, 12:58 AM
#31
Hey Guys, I'd like to clarify something:
There are several reasons why it would backfire into the intake. A broken distributer timing belt can easy be checked, but honestly, if that gives away, the car is pretty much undrivable. Flywheel sensor in example (say the gap is too great) would cause you a "cut-off" at certain rpm before it cuts back in. So, if you have a car that runs fine, but out of a sudden pops an intake during the start, you should be messuring your fuel pressure & holding pressure once engine is switched off. If the pressure is around 4.5 bar (thats what the pump supplies) you have no regulation as the nominal value is 3.3 +/- 0.2 bar (dont ring the alarm bells if you've got 3.6 or 3.7, they are not to accurate after all). As mentioned if far too high you most likely have a broken diaphram membrane in your regulator. Your holding pressure would than drop drastically after switching off the engine. During that time the remaining vacuum and rest pressure of the pump will push petrol through the vacuum line (that controls the regulator) into the intake and fills it up with fuel. During your next start that fuel will combust and lift your intake. A tip aside, a leaking injector has the same effect but can be excluded if your fuel pressure on a running engine is far too high (unless you have miracly 2 fault causes in the same time)...
I hope that helps some of you guys with your troubleshooting :-)
There are several reasons why it would backfire into the intake. A broken distributer timing belt can easy be checked, but honestly, if that gives away, the car is pretty much undrivable. Flywheel sensor in example (say the gap is too great) would cause you a "cut-off" at certain rpm before it cuts back in. So, if you have a car that runs fine, but out of a sudden pops an intake during the start, you should be messuring your fuel pressure & holding pressure once engine is switched off. If the pressure is around 4.5 bar (thats what the pump supplies) you have no regulation as the nominal value is 3.3 +/- 0.2 bar (dont ring the alarm bells if you've got 3.6 or 3.7, they are not to accurate after all). As mentioned if far too high you most likely have a broken diaphram membrane in your regulator. Your holding pressure would than drop drastically after switching off the engine. During that time the remaining vacuum and rest pressure of the pump will push petrol through the vacuum line (that controls the regulator) into the intake and fills it up with fuel. During your next start that fuel will combust and lift your intake. A tip aside, a leaking injector has the same effect but can be excluded if your fuel pressure on a running engine is far too high (unless you have miracly 2 fault causes in the same time)...
I hope that helps some of you guys with your troubleshooting :-)
07-24-2017, 04:51 AM
#32
Race Car
lots of good advice above ... i had a similar experience and never really tracked down what caused the backfire/bang which popped of the intake but generally the issue was:
an overfill of oil which meant
oil in intake and on injectors and sensors and the rubber cuffs on intake legs
and once that was sorted out everything went back to normal
an overfill of oil which meant
oil in intake and on injectors and sensors and the rubber cuffs on intake legs
and once that was sorted out everything went back to normal
07-24-2017, 05:00 AM
#33
Race Car
So, if you have a car that runs fine, but out of a sudden pops an intake during the start, you should be measuring your fuel pressure & holding pressure once engine is switched off. If the pressure is around 4.5 bar (thats what the pump supplies) you have no regulation as the nominal value is 3.3 +/- 0.2 bar (don't ring the alarm bells if you've got 3.6 or 3.7, they are not to accurate after all). As mentioned if far too high you most likely have a broken diaphram membrane in your regulator. Your holding pressure would than drop drastically after switching off the engine. During that time the remaining vacuum and rest pressure of the pump will push petrol through the vacuum line (that controls the regulator) into the intake and fills it up with fuel. During your next start that fuel will combust and lift your intake. A tip aside, a leaking injector has the same effect but can be excluded if your fuel pressure on a running engine is far too high (unless you have miracly 2 fault causes in the same time)...
I hope that helps some of you guys with your troubleshooting :-)
I hope that helps some of you guys with your troubleshooting :-)
a. while my fuel pressure was 4-5 it didn't fall off after shutdown .. pressure took a while to subside. Worth rechecking?
b. injectors are new 550cc Bosch Big greens as car is 3.8 w motec and the old injectors were running very full duty cycle so while checking them for residue etc.. and cleaning I didn't do anything else
Make sense?
07-24-2017, 11:10 AM
#34
HiWind,
You will surely need higher pressure injecting into a 3.8l. And as long as pressure doesnt discharge into the intake while the car is not running it should not burst off your intake.
It does puzzle me however how an overfill of oil causes a combustion within the intake....
You will surely need higher pressure injecting into a 3.8l. And as long as pressure doesnt discharge into the intake while the car is not running it should not burst off your intake.
It does puzzle me however how an overfill of oil causes a combustion within the intake....
07-24-2017, 11:45 AM
#35
Race Car
thanks Leo ... what I meant was the overfill resulted in oil seeping under the rubber boots and that made it easier for the intake to pop off, as well as confusing the afm, isv and generally causing havoc. As you say the combustion was likely injector related.
