Engine break-up under moderate to high loads
Mar 18, 2010, 11:13 PM
#1
Engine break-up under moderate to high loads
Just thought I'd bounce an issue I'm having with an Evo off a few more brains than just mine 
The car is running 96531706 ROM (v7 +SD) on e85. Running 27 psi peak boost via a MBC dropping to about 25 by redline. Stock turbo with Forge internal wastegate.
The issue is pretty heavy break up under full throttle pulls. The break up stops at higher rpm (6k to 7K) but, from about 2500 to 6k its pretty bad. Running conservative timing and afrs (10.8-11.3) with no knock as I am still trying to dial in boost.
Currently the car is running 1200cc FICs, Walbro 255lph pump and an Aeromotive fpr set at 55 psi with no vacuum (48 with vacuum) along with the SparkTech coil on plug kit.
My thought is that the fuel pump is not able to keep up with the fuel pressure the Aeromotive is asking for. The car had some minor break-up at high rpm high boost running C16 (with FIC 750s) prior but, its was very minor and inconsistent (never could capture it on a log). The break up has seemed to have gotten worse since installing the fpr, so I'm leaning towards that being the cause as it is asking for more pressure than the Walbro can provide.
I plan on setting the fpr to stock pressures to see if that is an improvement as well as turning the boost down.
Any thoughts?
The car is running 96531706 ROM (v7 +SD) on e85. Running 27 psi peak boost via a MBC dropping to about 25 by redline. Stock turbo with Forge internal wastegate. The issue is pretty heavy break up under full throttle pulls. The break up stops at higher rpm (6k to 7K) but, from about 2500 to 6k its pretty bad. Running conservative timing and afrs (10.8-11.3) with no knock as I am still trying to dial in boost.
Currently the car is running 1200cc FICs, Walbro 255lph pump and an Aeromotive fpr set at 55 psi with no vacuum (48 with vacuum) along with the SparkTech coil on plug kit.
My thought is that the fuel pump is not able to keep up with the fuel pressure the Aeromotive is asking for. The car had some minor break-up at high rpm high boost running C16 (with FIC 750s) prior but, its was very minor and inconsistent (never could capture it on a log). The break up has seemed to have gotten worse since installing the fpr, so I'm leaning towards that being the cause as it is asking for more pressure than the Walbro can provide.
I plan on setting the fpr to stock pressures to see if that is an improvement as well as turning the boost down.
Any thoughts?
Mar 20, 2010, 12:15 PM
#4
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Gap the plugs to 24-22...
I was able to run 33psi on the stock 9 turbo gaped to 32 but got an occasional misfire... closed them to 24 and never see problems anymore...
My hta35r see's 33psi at this gap as well...
Running the DENSO iridiums for IX.
BPR8es gapped to 24 should do the trick.
I was able to run 33psi on the stock 9 turbo gaped to 32 but got an occasional misfire... closed them to 24 and never see problems anymore...
My hta35r see's 33psi at this gap as well...
Running the DENSO iridiums for IX.
BPR8es gapped to 24 should do the trick.
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Mar 21, 2010, 12:08 PM
#8
The most common reason for mis-fires (other than bad AFRs
) is going to be ignition related. Either the plug is badly worn or was improperly gapped from the start or the ignition system is not up to the task you're putting it through. Also, mis-fires will show up as lean spikes in AFR if you're using a wideband that can pole the WBo2S fast enough to have the resolution to see the fast lean spikes.
A worn plug will do two things.
1. The electrode will wear and round. When this happens, it makes it hard for the spark to discharge and jump the gap to the ground strap. The electrode needs to have a sharp edge from which the spark can arc from. If the edges are rounded, the arc is less consistent. This is why i always push the Iridium plugs, because they wear slower and have a very small electrode from which the spark can arc easily, even when slightly worn.
2. As the electrode and ground strap erode, the gap opens up. If you were already very close to running the largest gap you could with your set-up, as these two variables erode, the gap will open and eventually be too big for the spark to jump, under load.
Also, the stock ignition system will have a hard timing keeping up at high boost levels and rich AFRs, this will require a smaller gap, which in turn, hinders the spark plugs ability to expose the ignition source to the fuel mixture. You want to run the largest gap you can get away with. Unfortunately, the stock system has it's limits and you'll eventually need to upgrade the ignition system in order to be able to run more gap.
Take my advice and go get a set of NGK Iridium IX plugs.
For non-MIVEC use:
Protruding tip: BPR*EIX(insert plug temp here*)
Non-Protruding tip: BR*EIX(insert plug temp here*)
side note: A non-protruding spark plug will run in half heat ranges. So a BR8EIX plug will be a heat range of 8.5(1.5 colder heat range than stock), whereas a BPR8EIX will be a heat range or 8(1 heat range cooler than stock). The higher the number, the colder the heat range. Stock heat range is 7 BTW(BPR7EIX).
The spark plug has two main jobs. 1. To ignite the air/fuel mixture. 2. To release heat from the combustion chamber through the plugs insulator and thus into the plug and heat sinked into the head where the coolant can transfer the heat away from the head. You must also make sure you're correctly torquing the plug, to insure a proper seat from which the plug can heat sink to the head.
~Cary
) is going to be ignition related. Either the plug is badly worn or was improperly gapped from the start or the ignition system is not up to the task you're putting it through. Also, mis-fires will show up as lean spikes in AFR if you're using a wideband that can pole the WBo2S fast enough to have the resolution to see the fast lean spikes.
A worn plug will do two things.
1. The electrode will wear and round. When this happens, it makes it hard for the spark to discharge and jump the gap to the ground strap. The electrode needs to have a sharp edge from which the spark can arc from. If the edges are rounded, the arc is less consistent. This is why i always push the Iridium plugs, because they wear slower and have a very small electrode from which the spark can arc easily, even when slightly worn.
2. As the electrode and ground strap erode, the gap opens up. If you were already very close to running the largest gap you could with your set-up, as these two variables erode, the gap will open and eventually be too big for the spark to jump, under load.
Also, the stock ignition system will have a hard timing keeping up at high boost levels and rich AFRs, this will require a smaller gap, which in turn, hinders the spark plugs ability to expose the ignition source to the fuel mixture. You want to run the largest gap you can get away with. Unfortunately, the stock system has it's limits and you'll eventually need to upgrade the ignition system in order to be able to run more gap.
Take my advice and go get a set of NGK Iridium IX plugs.
For non-MIVEC use:
Protruding tip: BPR*EIX(insert plug temp here*)
Non-Protruding tip: BR*EIX(insert plug temp here*)
side note: A non-protruding spark plug will run in half heat ranges. So a BR8EIX plug will be a heat range of 8.5(1.5 colder heat range than stock), whereas a BPR8EIX will be a heat range or 8(1 heat range cooler than stock). The higher the number, the colder the heat range. Stock heat range is 7 BTW(BPR7EIX).
The spark plug has two main jobs. 1. To ignite the air/fuel mixture. 2. To release heat from the combustion chamber through the plugs insulator and thus into the plug and heat sinked into the head where the coolant can transfer the heat away from the head. You must also make sure you're correctly torquing the plug, to insure a proper seat from which the plug can heat sink to the head.
~Cary
Mar 21, 2010, 12:24 PM
#9
The most common reason for mis-fires (other than bad AFRs
) is going to be ignition related. Either the plug is badly worn or was improperly gapped from the start or the ignition system is not up to the task you're putting it through. Also, mis-fires will show up as lean spikes in AFR if you're using a wideband that can pole the WBo2S fast enough to have the resolution to see the fast lean spikes.
A worn plug will do two things.
1. The electrode will wear and round. When this happens, it makes it hard for the spark to discharge and jump the gap to the ground strap. The electrode needs to have a sharp edge from which the spark can arc from. If the edges are rounded, the arc is less consistent. This is why i always push the Iridium plugs, because they wear slower and have a very small electrode from which the spark can arc easily, even when slightly worn.
2. As the electrode and ground strap erode, the gap opens up. If you were already very close to running the largest gap you could with your set-up, as these two variables erode, the gap will open and eventually be too big for the spark to jump, under load.
Also, the stock ignition system will have a hard timing keeping up at high boost levels and rich AFRs, this will require a smaller gap, which in turn, hinders the spark plugs ability to expose the ignition source to the fuel mixture. You want to run the largest gap you can get away with. Unfortunately, the stock system has it's limits and you'll eventually need to upgrade the ignition system in order to be able to run more gap.
Take my advice and go get a set of NGK Iridium IX plugs.
For non-MIVEC use:
Protruding tip: BPR*EIX(insert plug temp here*)
Non-Protruding tip: BR*EIX(insert plug temp here*)
side note: A non-protruding spark plug will run in half heat ranges. So a BR8EIX plug will be a heat range of 8.5(1.5 colder heat range than stock), whereas a BPR8EIX will be a heat range or 8(1 heat range cooler than stock). The higher the number, the colder the heat range. Stock heat range is 7 BTW(BPR7EIX).
The spark plug has two main jobs. 1. To ignite the air/fuel mixture. 2. To release heat from the combustion chamber through the plugs insulator and thus into the plug and heat sinked into the head where the coolant can transfer the heat away from the head. You must also make sure you're correctly torquing the plug, to insure a proper seat from which the plug can heat sink to the head.
~Cary
) is going to be ignition related. Either the plug is badly worn or was improperly gapped from the start or the ignition system is not up to the task you're putting it through. Also, mis-fires will show up as lean spikes in AFR if you're using a wideband that can pole the WBo2S fast enough to have the resolution to see the fast lean spikes.
A worn plug will do two things.
1. The electrode will wear and round. When this happens, it makes it hard for the spark to discharge and jump the gap to the ground strap. The electrode needs to have a sharp edge from which the spark can arc from. If the edges are rounded, the arc is less consistent. This is why i always push the Iridium plugs, because they wear slower and have a very small electrode from which the spark can arc easily, even when slightly worn.
2. As the electrode and ground strap erode, the gap opens up. If you were already very close to running the largest gap you could with your set-up, as these two variables erode, the gap will open and eventually be too big for the spark to jump, under load.
Also, the stock ignition system will have a hard timing keeping up at high boost levels and rich AFRs, this will require a smaller gap, which in turn, hinders the spark plugs ability to expose the ignition source to the fuel mixture. You want to run the largest gap you can get away with. Unfortunately, the stock system has it's limits and you'll eventually need to upgrade the ignition system in order to be able to run more gap.
Take my advice and go get a set of NGK Iridium IX plugs.
For non-MIVEC use:
Protruding tip: BPR*EIX(insert plug temp here*)
Non-Protruding tip: BR*EIX(insert plug temp here*)
side note: A non-protruding spark plug will run in half heat ranges. So a BR8EIX plug will be a heat range of 8.5(1.5 colder heat range than stock), whereas a BPR8EIX will be a heat range or 8(1 heat range cooler than stock). The higher the number, the colder the heat range. Stock heat range is 7 BTW(BPR7EIX).
The spark plug has two main jobs. 1. To ignite the air/fuel mixture. 2. To release heat from the combustion chamber through the plugs insulator and thus into the plug and heat sinked into the head where the coolant can transfer the heat away from the head. You must also make sure you're correctly torquing the plug, to insure a proper seat from which the plug can heat sink to the head.
~Cary
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