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Old 10-31-2006, 11:15 AM   #1
BadTrip
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Default Lean condition via low fuel pressure?

Gents,

I went for a tuning session on my modded VF-22/pinks/UTEC/USDM 2.0L a while back. In the week prior to the tune appointment I thought I'd gotten a bad tank of gas. I noticed pretty substantial knock under load/boost. Well I just settled in and drove the car under minimal boost, etc for a few days (100miles/day). Finally got the last of it out on the way to the tunner session. I put in two gallons of fresh 93 and drove it out (~50 miles on 2 gal), then repeated it again....2 gallons of 93 and drove it another ~50 miles. Ok...so I thought I was ready for the tuning session. Two more gallons of 93 and off we go for road tune.

Upgraded UTEC to new firmware version and I understood the tuner to say he was going to tune it via Speed Density technique.

During the initial road tune we never got a solid map established. Due to time constraints and the appointment with the dyno, we went ahead and loaded the car on the dyno, made a semi-baseline pull, and started working on the map. After four or five pulls we still hadn't really nailed the base 93 octane map and realized that we were very close to being out of fuel. I had brought some race gas for a race map and we put that in (5 Gal) rather than unstrap the car, etc, etc.
Well, when we cranked the car back up to tune, it was borked. It was running nasty lean. Wouldn't even idle without toying with the throttle. Tuner looks at me....I look, at him. .....spontaneous WTF?'s.
So.....to make along story short....I wound up limping home on the zero map. While on that zero map, my Tuna was reading a rock solid 14.7. I stayed out of boost......wondering if I was going to make it home.

Since then I've replaced the fuel filter and cobbled together a fuel pressure gauge in-line after the filter. It reads ~38psi at idle rising to ~60psi under load on that zero map.
What should my pressure be? Is there anything else I need to check before loading a OTS base map to start re-tuning with? Everything got blown away from the firmware upgrade....AND my laptop is currently unavailable (dual-purpose work computer and is being rebuilt by IT).

Comments? suggestions? Laugh at my expense?


Thanks in advance,
BadTrip
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Old 10-31-2006, 12:16 PM   #2
xcntrk75
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What pump are you running?

From what I've read those pressures seem fine, it anything a little high under load (although I haven't tested my own pressure to verify)...
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Old 10-31-2006, 12:23 PM   #3
BadTrip
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Standard upgraded pump...Walbro 255. I thought it must be the pump....called around and found that they are pretty solid units......two folks I spoke to who have sold hundreds a piece had only seen one go bad between them.
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Old 11-01-2006, 10:48 AM   #4
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bump for any ideas
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Old 11-01-2006, 04:22 PM   #5
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Clogged injector?
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Old 11-01-2006, 05:05 PM   #6
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I was under the impression that stock should be more like 44psi at idle. On boost fuel pressure would depend on what boost you are running as it's a 1:1 regulator. 38 seems a little low but the FPR seems to be working

Maybe you have a post MAF, pre-turbo leak? Un-measured air getting into the system..... Just a thought
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Old 11-01-2006, 05:29 PM   #7
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Quote:
Originally Posted by bcblues View Post
Clogged injector?
Wouldn't a clogged injector produce problems across the board? As opposed to running great off boost?

Thanks for the idea
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Old 11-01-2006, 05:35 PM   #8
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Quote:
Originally Posted by mick_the_ginge View Post
I was under the impression that stock should be more like 44psi at idle. On boost fuel pressure would depend on what boost you are running as it's a 1:1 regulator. 38 seems a little low but the FPR seems to be working

Maybe you have a post MAF, pre-turbo leak? Un-measured air getting into the system..... Just a thought

Yeah, I was expecting to see 43psi at idle.....but it was just a quickly cobbled up in-line fuel pressure gauge with a cheapo gauge. I figured it was close enough that it wasn't really indicative of a problem.
Yes, I agree that the FPR seems to be working.

I suppose you're suggestion of a post-MAF, pre-turbo leak would indeed produce this sort of outcome. Any techniques you'd suggest to help find a leak such as this? If I pressure test the system?

Am I still thinking clearly?.....that to produce this it's got to be unmetered air or not enough fuel? This shouldn't be from plugs, coil packs, etc, right?

Thanks again
Jon
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Old 11-01-2006, 05:38 PM   #9
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+1 on the post MAF leak idea but the spec says:

More than 130 8 (34.3 US gal, 28.6 Imp gal)/h
[12 V at 300 kPa (3.06 kg/cm2, 43.5 psi)]
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Old 11-02-2006, 08:57 AM   #10
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Quote:
Originally Posted by cdvma View Post
+1 on the post MAF leak idea but the spec says:

More than 130 8 (34.3 US gal, 28.6 Imp gal)/h
[12 V at 300 kPa (3.06 kg/cm2, 43.5 psi)]
Thanks
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Old 11-02-2006, 05:27 PM   #11
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Maybe it is partially clogged and it flows enough at low IDCs to run great, but not at increased IDCs? I dunno, just throwing out an idea.

Quote:
Originally Posted by BadTrip View Post
Wouldn't a clogged injector produce problems across the board? As opposed to running great off boost?

Thanks for the idea
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Old 11-02-2006, 07:35 PM   #12
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how about a bad front o2 sensor?
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Old 11-03-2006, 02:24 PM   #13
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Quote:
Originally Posted by bcblues View Post
Maybe it is partially clogged and it flows enough at low IDCs to run great, but not at increased IDCs? I dunno, just throwing out an idea.
Al ideas are welcomed bro! thanks
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Old 11-03-2006, 02:26 PM   #14
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Quote:
Originally Posted by hippy View Post
how about a bad front o2 sensor?
meh? I don't mean to be a dumbarse......how would the front O2 sensor make me run lean? 'splain me
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Old 11-03-2006, 07:47 PM   #15
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The ecu uses the front o2 sensor to detect the a/f ratio while at part throttle. If it's wearing out, the ecu might think the a/f ratio is 14.7 when it's really not. Your tuna reading 14.7 to 1 makes me think this isn't the problem, but...?

peace
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Old 11-06-2006, 08:19 AM   #16
BadTrip
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Quote:
Originally Posted by hippy View Post
The ecu uses the front o2 sensor to detect the a/f ratio while at part throttle. If it's wearing out, the ecu might think the a/f ratio is 14.7 when it's really not. Your tuna reading 14.7 to 1 makes me think this isn't the problem, but...?

peace
Ahh! I suppose that could cause some screwy stuff to happen though. thanks for pointing that out.
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Old 11-06-2006, 08:29 AM   #17
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Quote:
Originally Posted by mick_the_ginge View Post
I was under the impression that stock should be more like 44psi at idle. On boost fuel pressure would depend on what boost you are running as it's a 1:1 regulator. 38 seems a little low but the FPR seems to be working

Maybe you have a post MAF, pre-turbo leak? Un-measured air getting into the system..... Just a thought
43.5psi FP is with the FPR vacume line disconected at idle. Put some vacume on the FPR and the FP drops 1:1 just like it will raise 1:1.

TMS
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Old 11-06-2006, 08:40 AM   #18
BadTrip
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Quote:
Originally Posted by TheMadScientist View Post
43.5psi FP is with the FPR vacume line disconected at idle. Put some vacume on the FPR and the FP drops 1:1 just like it will raise 1:1.

TMS
So then if I understand correctly.....if I'm pulling a bit of vaccum at idle, the 38psi sounds closer to correct than to being indicativbe of fuel pressure or FPR problem.
TMS, have you ever heard of one of the Walbro pumps going bad? or actually heard one under durress?

My mian problem is time. I just need to take a vacation day to work on it a bit to get it straightenend out.

Thanks for the post/info
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Old 11-06-2006, 01:23 PM   #19
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i thought i had a bad walbro once.

ended up being a bad tank of gas contaminated the sock.

took it all apart, cleaned it with toluene, blew it out with air, and after i reinstalled it everything was cool.

symptoms in my case were an inability to pull fuel when levels were low and it was sloshing around in the tank. anything under 1/3rd tank would do it.
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