High injector D.C.'s
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Joined: Jun 2008
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From: Bridgewater Ma.
High injector D.C.'s
The other day I was tweaking the minm. air setting on a new replacement TB. Trying to get the IAC counts down to around the 20's, (they were in the mid 70's @ idle) using datamaster.
While data logging on a short cruise I noticed the DC of my Bosch III's in the mid 90's under WOT. After completing the injector swap last year the DC was around 80 @ WOT.
First thing comes to mind is low fuel pressure. So I connect the FP gauge, static is 42 but bleeds down rapidly. I then tape the gauge to the windshield and hit the road. Pressure seems normal, 38-40ish with one exception, under moderate load or WOT, the FPG needle fluctuates rapidly between 30 to 40. As speed picks up or load lessens the needle smoothes out and returns to normal.
I know I need to perform further diagnosis of the fuel system, i.e. regulator (rebuilt in 08) / pulsator checks, just wondering what others think.
Fuel pump on the way out?
While data logging on a short cruise I noticed the DC of my Bosch III's in the mid 90's under WOT. After completing the injector swap last year the DC was around 80 @ WOT.
First thing comes to mind is low fuel pressure. So I connect the FP gauge, static is 42 but bleeds down rapidly. I then tape the gauge to the windshield and hit the road. Pressure seems normal, 38-40ish with one exception, under moderate load or WOT, the FPG needle fluctuates rapidly between 30 to 40. As speed picks up or load lessens the needle smoothes out and returns to normal.
I know I need to perform further diagnosis of the fuel system, i.e. regulator (rebuilt in 08) / pulsator checks, just wondering what others think.
Fuel pump on the way out?
Last edited by EastCoastHD; Apr 26, 2010 at 09:59 PM.
Le Mans Master
Joined: Jul 2007
Posts: 5,043
Likes: 8
From: Tampa Florida
I'm guessing this is a L98 car?
Did you go larger on the TB size than what you replaced?
Oversized or aftermarket TBs can be very picky when it comes to dialing in the throttle stop screw. From what you've posted turn the screw "in" just a hair to allow a bit more air to slip by the blades then let the IAC do it's thing or reset the IAC using the IAC reset instruction in your FSM...it should come down. Recheck the TPS sensor voltage if applicable for your year.
Perhaps your getting more air through new TB to the engine and the injectors are being run at a higher cycle because of it.
The very noticable bounce in the fuel gauge is represenative of the amount of fuel being used during the injector pules...this bounce is not uncommon at higher or WOT positions.
If the regulator was replaced in '08 the I'd be willing to bet it is still fine. You may want to pull the fuel pump and replace it and the pulsator module if you feel it is related to your quick fuel pressure bleed down times. Here is a inexpensive fuel pump, pulsator modulator bypass hose and electrical harness offered by Poopboys: http://c2c.activant.com/ctoc/index.j...FAUxoWAFAJVHYf
Get a new fuel pump strainer "sock" also.
Did you go larger on the TB size than what you replaced?
Oversized or aftermarket TBs can be very picky when it comes to dialing in the throttle stop screw. From what you've posted turn the screw "in" just a hair to allow a bit more air to slip by the blades then let the IAC do it's thing or reset the IAC using the IAC reset instruction in your FSM...it should come down. Recheck the TPS sensor voltage if applicable for your year.
Perhaps your getting more air through new TB to the engine and the injectors are being run at a higher cycle because of it.
The very noticable bounce in the fuel gauge is represenative of the amount of fuel being used during the injector pules...this bounce is not uncommon at higher or WOT positions.
If the regulator was replaced in '08 the I'd be willing to bet it is still fine. You may want to pull the fuel pump and replace it and the pulsator module if you feel it is related to your quick fuel pressure bleed down times. Here is a inexpensive fuel pump, pulsator modulator bypass hose and electrical harness offered by Poopboys: http://c2c.activant.com/ctoc/index.j...FAUxoWAFAJVHYf
Get a new fuel pump strainer "sock" also.
Thread Starter
Instructor
Joined: Jun 2008
Posts: 138
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From: Bridgewater Ma.
I'm guessing this is a L98 car?
Did you go larger on the TB size than what you replaced?
Yes, its a stock L98. Yes, its a BBK 52 mm. I used this in lieu of not being able to locate a stock replacement.
Oversized or aftermarket TBs can be very picky when it comes to dialing in the throttle stop screw. From what you've posted turn the screw "in" just a hair to allow a bit more air to slip by the blades then let the IAC do it's thing or reset the IAC using the IAC reset instruction in your FSM...it should come down. Recheck the TPS sensor voltage if applicable for your year.
Perhaps your getting more air through new TB to the engine and the injectors are being run at a higher cycle because of it.
Doesn't this contradict what others have stated /demonstrated that increasing the TB will net no performance improvement on a stock engine due to restictions in the other parts of the induction system. In other words very little if any increased airflow.
The very noticable bounce in the fuel gauge is represenative of the amount of fuel being used during the injector pules...this bounce is not uncommon at higher or WOT positions.
Hmmm, first time I have heard of this. No mention in the FSM. But it makes sense to me.
If the regulator was replaced in '08 the I'd be willing to bet it is still fine. You may want to pull the fuel pump and replace it and the pulsator module if you feel it is related to your quick fuel pressure bleed down times.
I agree. I think in the end, this will probably end up being the problem.
Here is a inexpensive fuel pump, pulsator modulator bypass hose and electrical harness offered by Poopboys: http://c2c.activant.com/ctoc/index.j...FAUxoWAFAJVHYf
Get a new fuel pump strainer "sock" also.
Did you go larger on the TB size than what you replaced?
Yes, its a stock L98. Yes, its a BBK 52 mm. I used this in lieu of not being able to locate a stock replacement.
Oversized or aftermarket TBs can be very picky when it comes to dialing in the throttle stop screw. From what you've posted turn the screw "in" just a hair to allow a bit more air to slip by the blades then let the IAC do it's thing or reset the IAC using the IAC reset instruction in your FSM...it should come down. Recheck the TPS sensor voltage if applicable for your year.
Perhaps your getting more air through new TB to the engine and the injectors are being run at a higher cycle because of it.
Doesn't this contradict what others have stated /demonstrated that increasing the TB will net no performance improvement on a stock engine due to restictions in the other parts of the induction system. In other words very little if any increased airflow.
The very noticable bounce in the fuel gauge is represenative of the amount of fuel being used during the injector pules...this bounce is not uncommon at higher or WOT positions.
Hmmm, first time I have heard of this. No mention in the FSM. But it makes sense to me.
If the regulator was replaced in '08 the I'd be willing to bet it is still fine. You may want to pull the fuel pump and replace it and the pulsator module if you feel it is related to your quick fuel pressure bleed down times.
I agree. I think in the end, this will probably end up being the problem.
Here is a inexpensive fuel pump, pulsator modulator bypass hose and electrical harness offered by Poopboys: http://c2c.activant.com/ctoc/index.j...FAUxoWAFAJVHYf
Get a new fuel pump strainer "sock" also.
Thread Starter
Instructor
Joined: Jun 2008
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From: Bridgewater Ma.
OK. I was able to perform further troubleshooting today.
Fuel pressure leakdown test.
Engine running at idle, 35 psi.
Key to "on" engine "off". Pressure peaks at 44 psi, once the pump stops, the pressure quickly snaps down to 38-40. Then it continues to rapidly bleed off in 10 secs. down to 30 psi, 30 secs. down to 24 psi. In 1 min. it is down to 20 psi.
Pinch off the pressure hose at the tank, still bleeds off pressure. Same rate as previous.
Pinch off the return hose at the tank, still bleeds off pressure. Same rate as previous.
Next I pinch off the return prior to turning the key to "on" engine "off".
As expected pressure peaks at 72 psi., slowly drops to 68 and holds upto ten mins.
Why / how would it hold at a higher pressure? Is the higher pressure causing a faulty injector(s) to seat properly and not leak?
With multiple leak down tests indicating a leaking injector(s), I figured there would be plenty of fuel in a cylinder so I pulled the dizzy feed and spun the engine a few times thinking it might throw some fuel onto the plugs. After pulling all the plugs and inspecting them, they all appeared normal no evidence of fuel fouling, nice and dry.
I know that to accurately test the injectors for leakage they need to be pulled from the lower intake pressurized and inspected, my question is they are Bosch III's, no clips installed, will they pop out of the rails when pressurized?
All comments welcome here, have I missed anything?
Fuel pressure leakdown test.
Engine running at idle, 35 psi.
Key to "on" engine "off". Pressure peaks at 44 psi, once the pump stops, the pressure quickly snaps down to 38-40. Then it continues to rapidly bleed off in 10 secs. down to 30 psi, 30 secs. down to 24 psi. In 1 min. it is down to 20 psi.
Pinch off the pressure hose at the tank, still bleeds off pressure. Same rate as previous.
Pinch off the return hose at the tank, still bleeds off pressure. Same rate as previous.
Next I pinch off the return prior to turning the key to "on" engine "off".
As expected pressure peaks at 72 psi., slowly drops to 68 and holds upto ten mins.
Why / how would it hold at a higher pressure? Is the higher pressure causing a faulty injector(s) to seat properly and not leak?
With multiple leak down tests indicating a leaking injector(s), I figured there would be plenty of fuel in a cylinder so I pulled the dizzy feed and spun the engine a few times thinking it might throw some fuel onto the plugs. After pulling all the plugs and inspecting them, they all appeared normal no evidence of fuel fouling, nice and dry.
I know that to accurately test the injectors for leakage they need to be pulled from the lower intake pressurized and inspected, my question is they are Bosch III's, no clips installed, will they pop out of the rails when pressurized?
All comments welcome here, have I missed anything?
Supporting Vendor
Joined: Mar 2008
Posts: 1,762
Likes: 14
From: Cumming Ga
OK. I was able to perform further troubleshooting today.
Fuel pressure leakdown test.
Engine running at idle, 35 psi.
Key to "on" engine "off". Pressure peaks at 44 psi, once the pump stops, the pressure quickly snaps down to 38-40. Then it continues to rapidly bleed off in 10 secs. down to 30 psi, 30 secs. down to 24 psi. In 1 min. it is down to 20 psi.
Pinch off the pressure hose at the tank, still bleeds off pressure. Same rate as previous.
Pinch off the return hose at the tank, still bleeds off pressure. Same rate as previous.
Next I pinch off the return prior to turning the key to "on" engine "off".
As expected pressure peaks at 72 psi., slowly drops to 68 and holds upto ten mins.
Why / how would it hold at a higher pressure? Is the higher pressure causing a faulty injector(s) to seat properly and not leak?
With multiple leak down tests indicating a leaking injector(s), I figured there would be plenty of fuel in a cylinder so I pulled the dizzy feed and spun the engine a few times thinking it might throw some fuel onto the plugs. After pulling all the plugs and inspecting them, they all appeared normal no evidence of fuel fouling, nice and dry.
I know that to accurately test the injectors for leakage they need to be pulled from the lower intake pressurized and inspected, my question is they are Bosch III's, no clips installed, will they pop out of the rails when pressurized?
All comments welcome here, have I missed anything?
Fuel pressure leakdown test.
Engine running at idle, 35 psi.
Key to "on" engine "off". Pressure peaks at 44 psi, once the pump stops, the pressure quickly snaps down to 38-40. Then it continues to rapidly bleed off in 10 secs. down to 30 psi, 30 secs. down to 24 psi. In 1 min. it is down to 20 psi.
Pinch off the pressure hose at the tank, still bleeds off pressure. Same rate as previous.
Pinch off the return hose at the tank, still bleeds off pressure. Same rate as previous.
Next I pinch off the return prior to turning the key to "on" engine "off".
As expected pressure peaks at 72 psi., slowly drops to 68 and holds upto ten mins.
Why / how would it hold at a higher pressure? Is the higher pressure causing a faulty injector(s) to seat properly and not leak?
With multiple leak down tests indicating a leaking injector(s), I figured there would be plenty of fuel in a cylinder so I pulled the dizzy feed and spun the engine a few times thinking it might throw some fuel onto the plugs. After pulling all the plugs and inspecting them, they all appeared normal no evidence of fuel fouling, nice and dry.
I know that to accurately test the injectors for leakage they need to be pulled from the lower intake pressurized and inspected, my question is they are Bosch III's, no clips installed, will they pop out of the rails when pressurized?
All comments welcome here, have I missed anything?
Thread Starter
Instructor
Joined: Jun 2008
Posts: 138
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From: Bridgewater Ma.
wierd problem.. The higher pressure might hold a leaker closed, even if you have clips, unless the plenum is off you cannot lift the rails high enough to do a visual check.. Not, having any fuel in the cylinders is not indicative of a leaky injector, but your symptoms are. You can pull out bosch 3's without removing the plenum. Take them out and send them to me. I will test them, if any are leaking I will replace them, you have a three year warranty..
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Thread Starter
Instructor
Joined: Jun 2008
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From: Bridgewater Ma.
Thanks for chiming in Jon.
Runs good. What led to discovering the fuel pressure issue was a sluggish start on a warm engine. I compare it to a lazy choke on a carb. Seemed as though it wasnt getting enough fuel or to much. No smoke from the exhaust or stumble.
I found a thread on this forum discussing "minm. air flow". I realized that maybe my problem. Soon after replacing my injectors in 08, I replaced my TB (binding throttle shaft) with a BBK 52 mm. unit. I installed it with no adjustments.
Recently after running datamaster I noticed IAC counts around mid 70's at idle. I got it down to the mid twenties. It seemed to help the sluggish start to where it is barely noticable. Which leads me to think it might be "rich" at start up and cracking the throttle a bit more is leaning things out some.
Latest log, BLM's (all over the place), knock counts and DC (90 @ WOT) dont seem correct.
Jon, can you explain the high DC's ?
Runs good. What led to discovering the fuel pressure issue was a sluggish start on a warm engine. I compare it to a lazy choke on a carb. Seemed as though it wasnt getting enough fuel or to much. No smoke from the exhaust or stumble.
I found a thread on this forum discussing "minm. air flow". I realized that maybe my problem. Soon after replacing my injectors in 08, I replaced my TB (binding throttle shaft) with a BBK 52 mm. unit. I installed it with no adjustments.
Recently after running datamaster I noticed IAC counts around mid 70's at idle. I got it down to the mid twenties. It seemed to help the sluggish start to where it is barely noticable. Which leads me to think it might be "rich" at start up and cracking the throttle a bit more is leaning things out some.
Latest log, BLM's (all over the place), knock counts and DC (90 @ WOT) dont seem correct.
Jon, can you explain the high DC's ?
Last edited by EastCoastHD; Apr 29, 2010 at 06:13 AM.
Supporting Vendor
Joined: Mar 2008
Posts: 1,762
Likes: 14
From: Cumming Ga
Thanks for chiming in Jon.
Runs good. What led to discovering the fuel pressure issue was a sluggish start on a warm engine. I compare it to a lazy choke on a carb. Seemed as though it wasnt getting enough fuel or to much. No smoke from the exhaust or stumble.
I found a thread on this forum discussing "minm. air flow". I realized that maybe my problem. Soon after replacing my injectors in 08, I replaced my TB (binding throttle shaft) with a BBK 52 mm. unit. I installed it with no adjustments.
Recently after running datamaster I noticed IAC counts around mid 70's at idle. I got it down to the mid twenties. It seemed to help the sluggish start to where it is barely noticable. Which leads me to think it might be "rich" at start up and cracking the throttle a bit more is leaning things out some.
Latest log, BLM's (all over the place), knock counts and DC (90 @ WOT) dont seem correct.
Jon, can you explain the high DC's ?
Runs good. What led to discovering the fuel pressure issue was a sluggish start on a warm engine. I compare it to a lazy choke on a carb. Seemed as though it wasnt getting enough fuel or to much. No smoke from the exhaust or stumble.
I found a thread on this forum discussing "minm. air flow". I realized that maybe my problem. Soon after replacing my injectors in 08, I replaced my TB (binding throttle shaft) with a BBK 52 mm. unit. I installed it with no adjustments.
Recently after running datamaster I noticed IAC counts around mid 70's at idle. I got it down to the mid twenties. It seemed to help the sluggish start to where it is barely noticable. Which leads me to think it might be "rich" at start up and cracking the throttle a bit more is leaning things out some.
Latest log, BLM's (all over the place), knock counts and DC (90 @ WOT) dont seem correct.
Jon, can you explain the high DC's ?
Thread Starter
Instructor
Joined: Jun 2008
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From: Bridgewater Ma.
high blm means its adding fuel. You added air without modifying the VE tables. I think that might be the underlying problem. The high BLM won't hurt anything as long as it stays under 160. The ECU will keep it within the desired A/F ratio by widening the pulse width, hence, a higher DS
Supporting Vendor
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Posts: 1,762
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From: Cumming Ga
Makes sense in part. I can understand how adjusting the throttle plate coupled with a free flowing KN filter attached directly to the TB in my case (couldnt fit the OEM inlet to the 52 mm. TB) will increase air flow @ idle. But, once off idle and at WOT, dont see how this will effect inj. DC's or require adjustments to the VE tables
Thread Starter
Instructor
Joined: Jun 2008
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From: Bridgewater Ma.
I tried exporting to a .csv file so I could post them, no go.
Can I attach the file to an e-mail?
In the time it takes me to figure out how to send / display the files, I could have the injectors out.
Speaking of, disconnect hard lines at front of rails, remove 4 retaining bolts, remove injectors?
Jon, any special instructions on returning?
Last edited by EastCoastHD; Apr 29, 2010 at 05:34 PM.
Supporting Vendor
Joined: Mar 2008
Posts: 1,762
Likes: 14
From: Cumming Ga
Yes I have files. Getting them to you will be a challenge
I tried exporting to a .csv file so I could post them, no go.
Can I attach the file to an e-mail?
In the time it takes me to figure out how to send / display the files, I could have the injectors out.
Speaking of, disconnect hard lines at front of rails, remove 4 retaining bolts, remove injectors?
Jon, any special instructions on returning?
I tried exporting to a .csv file so I could post them, no go.
Can I attach the file to an e-mail?
In the time it takes me to figure out how to send / display the files, I could have the injectors out.
Speaking of, disconnect hard lines at front of rails, remove 4 retaining bolts, remove injectors?
Jon, any special instructions on returning?
Thread Starter
Instructor
Joined: Jun 2008
Posts: 138
Likes: 0
From: Bridgewater Ma.
view the file.. take a snap shot by hitting print screen.. save it as a jpeg and attach it to an e mail.. i will see it as a photo.. removing the injectors is easy// loosen the rail push all the right bank injectors up in the rail. tilt the left bank up and remove them.. then take out the right bank. Reinstall the same way with a lot of Vaseline so when the injector is up in the rail, it will slide down easy..
