Newer build in a Mercury Marauder that aint been right yet...
4.6 DOHC with centri blower @ 16ish PSI, decent size custom intercooler, alkycontrol, longtubes, forged rotating assembly, "custom cams/springs/valves" (I don’t really have cam specs I can trust)," 9.5:1 CR (or so I was told).
Did a compression test last night, engine warm after sitting an hour or so after drive home, all plugs out, fuel pump disabled, throttle open.
My good gauge didn’t fit, so I used the rental Compression tester from AutoZone (crappy gauge, but seemed consistent enough).
Results something like this:
Bank1:
125+
130-
125
130+
Bank2:
140+
145+
140-
145
After several measurements in each hole, and back and forth between banks; there seems to be a definite 10ish PSI average delta between banks, and a 20ish PSI high to low.
I did add a little oil to one hole in each side and measured again, which seemed to bring up the readings maybe 3-5psi in both of those I put oil in. Not real sure if that difference means much? Would oil on the rings bringing it up a few pounds indicate any ring issues? I know if oil on the rings brings up the compression, it points to worn rings; but how much difference in pressure after putting oil on rings indicates a real problem?
What I am thinking is that the cams may be a bit out of phase???
Something I also thought was odd, is that the motor seemed to turn over slower with all the plugs out, and throttle opened than it did with the plugs in? I actually pulled the truck over and hooked it up to my battery to run while I checked compression just to see if it would crank any faster and it did not. When I put the plugs back in and went to start it again, it seemed to crank fine and started right up?
This build has been slow going all year, I've had a shop do all the work and tuning, none of which has not gone well to say the least.
I have consistently had one bank richer than the other, which has shown in the STFTs, and in the widebands (one in each bank). When I look at O2 voltage, it also seems to match what the WBs and STFTs are reading.
Lately, the STFTs seem to move wildy from .90-1.00 in one bank and 1.00 to 115 in the other. Seems like they are often 10-15% apart.
When monitoring the STFTs before the build, the trims always seem to move much more slowly and stay pretty close to 1.00. Now they constantly sweep back and forth very quickly. They do sometimes stay a bit closer together, but vary enough to make it difficult to determine at what RPM or load level they like to settle down.
Then on a WOT pull, I have seen them vary a full AFR point or more.
The shop has told me I am chasing too many details and I should ignore it; but he said the delta could be caused by bad factory O2s, coils, or one injector that is slightly off. So I have recently swapped in new Motorcraft O2 sensors and all MSD new coils. I had planned to swap injectors between banks to see if problem follows injectors, but haven’t gotten to it yet.
Now after seeing the deltas in the compression test, I am seriously doubting its an injector issue. Just to be clear, these were already brand new Siemens Deka 60lb injectors, but were not a flow-matched set.
Trying to get to the point of cutting bait with the shop; but would like to know where I stand before potentially getting into it with those guys.
Thank for reading guys!
Any thoughts?
Am I getting too far into the weeds?
4.6 DOHC with centri blower @ 16ish PSI, decent size custom intercooler, alkycontrol, longtubes, forged rotating assembly, "custom cams/springs/valves" (I don’t really have cam specs I can trust)," 9.5:1 CR (or so I was told).
Did a compression test last night, engine warm after sitting an hour or so after drive home, all plugs out, fuel pump disabled, throttle open.
My good gauge didn’t fit, so I used the rental Compression tester from AutoZone (crappy gauge, but seemed consistent enough).
Results something like this:
Bank1:
125+
130-
125
130+
Bank2:
140+
145+
140-
145
After several measurements in each hole, and back and forth between banks; there seems to be a definite 10ish PSI average delta between banks, and a 20ish PSI high to low.
I did add a little oil to one hole in each side and measured again, which seemed to bring up the readings maybe 3-5psi in both of those I put oil in. Not real sure if that difference means much? Would oil on the rings bringing it up a few pounds indicate any ring issues? I know if oil on the rings brings up the compression, it points to worn rings; but how much difference in pressure after putting oil on rings indicates a real problem?
What I am thinking is that the cams may be a bit out of phase???
Something I also thought was odd, is that the motor seemed to turn over slower with all the plugs out, and throttle opened than it did with the plugs in? I actually pulled the truck over and hooked it up to my battery to run while I checked compression just to see if it would crank any faster and it did not. When I put the plugs back in and went to start it again, it seemed to crank fine and started right up?
This build has been slow going all year, I've had a shop do all the work and tuning, none of which has not gone well to say the least.
I have consistently had one bank richer than the other, which has shown in the STFTs, and in the widebands (one in each bank). When I look at O2 voltage, it also seems to match what the WBs and STFTs are reading.
Lately, the STFTs seem to move wildy from .90-1.00 in one bank and 1.00 to 115 in the other. Seems like they are often 10-15% apart.
When monitoring the STFTs before the build, the trims always seem to move much more slowly and stay pretty close to 1.00. Now they constantly sweep back and forth very quickly. They do sometimes stay a bit closer together, but vary enough to make it difficult to determine at what RPM or load level they like to settle down.
Then on a WOT pull, I have seen them vary a full AFR point or more.
The shop has told me I am chasing too many details and I should ignore it; but he said the delta could be caused by bad factory O2s, coils, or one injector that is slightly off. So I have recently swapped in new Motorcraft O2 sensors and all MSD new coils. I had planned to swap injectors between banks to see if problem follows injectors, but haven’t gotten to it yet.
Now after seeing the deltas in the compression test, I am seriously doubting its an injector issue. Just to be clear, these were already brand new Siemens Deka 60lb injectors, but were not a flow-matched set.
Trying to get to the point of cutting bait with the shop; but would like to know where I stand before potentially getting into it with those guys.
Thank for reading guys!
Any thoughts?
Am I getting too far into the weeds?
