Runs lean : Tune or Fuel Delivery?

[zquez]

As some of you may recall, I've had a myriad of fuel delivery problems. After the car was tuned in May of 2012 by Pro Dyno the car ran great - as far as I can remember. Shortly after, I had the fuel hose on the hat rupture and blow out. Since then, I also had the liner in the fuel line in the engine bay become dis-bonded and cause the fuel rail to essentially be plugged up as documented here:

http://www.s197forum.com/forum/showthread.php?t=97070

While the car runs better now that those issues have been resolved, it still runs lean throughout the whole RPM band and especially in first gear. The car will stumble under various loads- mostly from a stop, rough idle, gas mileage sucks (210ish), and overall the car feels like a total dog. Throttle response is nonexistent and I have to dump the clutch to even chirp the tires from a stop. I feel like a positive displacement blown, 450 whp V8 shouldn't drive this way. As a friend put it: "it definitely feels like a good running small block, but not a 500 hp supercharged monster."

My symptoms say to me that I have clogged/bad fuel injector(s). The car has loads of power when its still cold but once it heats up, it falls on its face. My thinking is that the problem I had with the fuel line post fuel filter allowed some debris/glue/whatever to cause a blockage in one or more of my injectors. This would explain the stumbling, idle, and poor gas mileage. The car sees that its running lean once it warms up and pulls timing hence the lack of power everywhere.

My notable mods are as follows:
DOB manifold with stock GT500 Eaton blower
GT500 47 lb/hr injectors
Walbro 405 fuel pump
Offroad x pipe
stock mufflers
TR6060

If it's not the injectors, I suspect the tune. I only have enough money right now to get a tune done by Lito or to get new injectors so I'm looking for advice here. Any other suggestions?

 

[skwerl]

What size injectors? I have the Roush supplied 39lb short injectors I just pulled off my motor. New motor is getting 48lb injectors so these are available.

 

[bcb06gt]

It would be hard for me to say the issue is tune related since the car ran fine after tune. Car had trouble once fuel problems started.

 

[Bobby]

just have dan check it to see what is going on, he will data log it and should be able to tell you something.

 

[zquez]

What size injectors? I have the Roush supplied 39lb short injectors I just pulled off my motor. New motor is getting 48lb injectors so these are available.

47lb. I suppose I would need a re-tune if I dropped rate.

It would be hard for me to say the issue is tune related since the car ran fine after tune. Car had trouble once fuel problems started.

My thinking as well.

just have dan check it to see what is going on, he will data log it and should be able to tell you something.

I like Dan a lot, but I've been over there 3 times and we couldn't figure out what it was. The only thing he had for me was that the throttle didn't seem like it was opening all the way. This was before I figured out the fuel line problem. Lito was actually able to tell me right off the bat that it was a fuel problem just by looking at my logs.

 

[blownGTvert]

Send the injectors out for servicing/ cleaning. Prob a good idea anyhow given the debris you had in the fuel system. See if runs better after the injector servicing.

 

[zquez]

Send the injectors out for servicing/ cleaning. Prob a good idea anyhow given the debris you had in the fuel system. See if runs better after the injector servicing.

I was going to do this, but it costs almost as much as new injectors, something like a difference of $20.

 

[Dubstep Shep]

Dumb questions ahead, but I figure I'll ask anyway.

Have you logged fuel pump pressure and voltage? If it's trying to add more fuel but it's clogged, that should show up as a discrepancy between those two. A tune wouldn't have a discrepancy between those two.

 

[Goinpro]

Getting a slight misfire? Sounds exactly like the issues I've had. You could really only hear the misfire when in throttle. It was very subtle in idle. Car was a dog...just needed a new spark plug, and it runs great now. I actually thought mine was an injector issue too, since I replaced the bad plug. Problem is that I replaced it with another bad one.

Did you try disconnecting the COP wires one at a time (leaving 7 connected) and listening for changes in idle? Finding one that results in no change should at least help you identify the cylinder with the issue, if it's a misfire issue.

 

[michael.konor]

Since you've had debonding in fuel lines, the internal fuel filter screens in your one or more of your injectors have to be clogged. That junk had to go somewhere.

As a quick check, have you pulled the injectors out of the fuel rail and checked the tops? Then turn them over and tap a few times and see what falls out?

 

[zquez]

Dumb questions ahead, but I figure I'll ask anyway.

Have you logged fuel pump pressure and voltage? If it's trying to add more fuel but it's clogged, that should show up as a discrepancy between those two. A tune wouldn't have a discrepancy between those two.

I haven't had time to do any recent datalogging but the symptoms were the same when I did this one:

@ 6004 RPM

58% duty cycle
Fuel Rail PSI 39.77
FPUMP_ACT_VOLTS 9.50
FPUMP_VOLTS_TAB 9.82

Also, the computer wouldn't try to ramp up voltage from an injector issue because it takes its reading at the rail.

Getting a slight misfire? Sounds exactly like the issues I've had. You could really only hear the misfire when in throttle. It was very subtle in idle. Car was a dog...just needed a new spark plug, and it runs great now. I actually thought mine was an injector issue too, since I replaced the bad plug. Problem is that I replaced it with another bad one.

Did you try disconnecting the COP wires one at a time (leaving 7 connected) and listening for changes in idle? Finding one that results in no change should at least help you identify the cylinder with the issue, if it's a misfire issue.

Yes it is a slight misfire. It happens every few seconds while at idle and can be clearly heard when holding a rev at 3k. However, while driving its unnoticeable. I have disconnected COPs with no change and even done injectors and each caused a drop in rpm. Only a couple had less noticeable drops but it wasn't really repeatable. I replaced the plugs about 3k miles ago anyway so it's not those. I wouldn't rule out a COP, but the unplugging trick doesn't give me any conclusive results. No codes as well.

Since you've had debonding in fuel lines, the internal fuel filter screens in your one or more of your injectors have to be clogged. That junk had to go somewhere.

As a quick check, have you pulled the injectors out of the fuel rail and checked the tops? Then turn them over and tap a few times and see what falls out?

What I've done is pull the injectors and spray fuel injector cleaner into each one from the top and bottom. Without having an extra connector to pulse it with though, I'm afraid it didn't do much. I also flushed the rails with gas. I really feel like it is the injectors and if I could find replacements filters I would change those.

A look at what happened with my fuel line.

 

[Goinpro]

Yes it is a slight misfire. It happens every few seconds while at idle and can be clearly heard when holding a rev at 3k. However, while driving its unnoticeable. I have disconnected COPs with no change and even done injectors and each caused a drop in rpm. Only a couple had less noticeable drops but it wasn't really repeatable. I replaced the plugs about 3k miles ago anyway so it's not those. I wouldn't rule out a COP, but the unplugging trick doesn't give me any conclusive results. No codes as well.

I could be wrong, but I'm still guessing it's a plug. The fact that testing the injectors made a difference each time makes me think it's not an injector. Each time you unplug a COP where there's not a misfire, there will be a change. It's not a huge change. I couldn't even tell by looking at the needle. There was a small change in the exhaust note. I literally had to walk from the front of my car to the back to hear it clearly. The only one that didn't make that minor change to the exhaust note for me was cylinder 4. Changed out the cylinder 4 plug, and it's back to normal. Like I said, I replaced the cylinder 4 plug once and still had the issue. I changed it again, with another plug from the same set as the 2nd plug, and it worked fine.

You should get a code when you unplug the COPs. If you run a DTC scan, are you getting a P1000? It won't trigger a check engine light, but I believe it suppresses codes until you can complete an OBD drive cycle.

 

[zquez]

I could be wrong, but I'm still guessing it's a plug. The fact that testing the injectors made a difference each time makes me think it's not an injector. Each time you unplug a COP where there's not a misfire, there will be a change. It's not a huge change. I couldn't even tell by looking at the needle. There was a small change in the exhaust note. I literally had to walk from the front of my car to the back to hear it clearly. The only one that didn't make that minor change to the exhaust note for me was cylinder 4. Changed out the cylinder 4 plug, and it's back to normal. Like I said, I replaced the cylinder 4 plug once and still had the issue. I changed it again, with another plug from the same set as the 2nd plug, and it worked fine.

You should get a code when you unplug the COPs. If you run a DTC scan, are you getting a P1000? It won't trigger a check engine light, but I believe it suppresses codes until you can complete an OBD drive cycle.

The only code I have is P0689 which I get consistently. I have no idea what it means. If I do as you say I get a code for unplugging the COP. The biggest reason I don't think it's the plugs is because the problem remained after changing them.

 

[Dubstep Shep]

I haven't had time to do any recent datalogging but the symptoms were the same when I did this one:

@ 6004 RPM

58% duty cycle
Fuel Rail PSI 39.77
FPUMP_ACT_VOLTS 9.50
FPUMP_VOLTS_TAB 9.82

Also, the computer wouldn't try to ramp up voltage from an injector issue because it takes its reading at the rail.

Oh duh, forgot about that.

Still, Your fuel pressure and pump voltage should be somewhat of an indicator of a clog. Not sure how much of a difference 1 clogged injector would make, but in theory there should be some difference in pressure and voltage.

 

[BruceH]

Have you looked at the easy stuff yet? Things like a stuck bypass, disconnected vacuum line or other unmetered air?

 

[zquez]

Oh duh, forgot about that.

Still, Your fuel pressure and pump voltage should be somewhat of an indicator of a clog. Not sure how much of a difference 1 clogged injector would make, but in theory there should be some difference in pressure and voltage.

Sure. But I doubt I have an all out blockage. Each injector is working and flowing but there is a possibility that I have a slight clog. An 8-10% blockage will cause the symptoms I have.

If it is a fuel injector issue I can know for certain at least one of the ones on the driver side is faulty since that's the side my wideband is on.

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[Fullboogie]

A few thoughts: Those injectors will support way more than your horsepower. There are plenty of GT500's with 600+ HP and stock injectors. Granted there are two pumps, but at 450 HP your injectors are plenty big enough.

You need to be sure you are logging the correct FP voltage. There are many, and only one is the correct one.

Lastly, you are flying completely blind without datalogs. The software is free, and all you need is a laptop. There's no excuse not to datalog and find the problem.

 

[zquez]

A few thoughts: Those injectors will support way more than your horsepower. There are plenty of GT500's with 600+ HP and stock injectors. Granted there are two pumps, but at 450 HP your injectors are plenty big enough.

You need to be sure you are logging the correct FP voltage. There are many, and only one is the correct one.

Lastly, you are flying completely blind without datalogs. The software is free, and all you need is a laptop. There's no excuse not to datalog and find the problem.

The issue is not whether I'm running out of injector, but rather if my injectors are fouled. The car is running lean as my wideband has confirmed. What is causing it to be lean though?

I have datalogs, though none terribly recent. The pids I have been monitoring were suggested to me by lito so I trust them to be correct. As far as I can tell there is not a pid for injector duty cycle which would easily allow me to narrow down which if any injectors are faulty. Perhaps I will try and datalog on the way to work tomorrow, but I dont expect them to be any different than my last ones.

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[Fullboogie]

If you want to try a set of fresh 47 lb injectors, let me know. I'm happy to send you mine to see if that solves your problem. If they work and you want them, we can talk about a price. If not, send 'em back. Let me know.

 

[zquez]

Have you looked at the easy stuff yet? Things like a stuck bypass, disconnected vacuum line or other unmetered air?

I did. Nothing jumped out at me.

If you want to try a set of fresh 47 lb injectors, let me know. I'm happy to send you mine to see if that solves your problem. If they work and you want them, we can talk about a price. If not, send 'em back. Let me know.

That'd be awesome. PM sent.