Fuel Pump or Wiring Diagnostics

FatLee

New Member
Joined
Apr 26, 2020
Is the fuel pressure gauge the "be all" "end all" for diagnosing a fuel pump or pump wiring harness?
My hood mounted gauge shows fuel pressure rising with boost and doesn't show any interruption in FP but the car is sure acting like there is.
 
Do you have the gauge mounted where you can see it during some pulls and such? The gauge stays steady with the base pressure plus the boost pressure? What pressure are you running? How old is the pump and filter? What do the plugs look like? Do you log? What does the ignition look like? Is the computer pulling timing out?
 
Thanks for the reply
I have a hood mounted Ken Bell FP gauge and fuel pressure is a rock steady 43psi @ idle and rises steady 1psi with boost. I've been keeping it to around 5-8psi for obvious reasons, so 48-53psi with light pulls. The gauge shows no drop, no interruption. I have a new pump and hot wire kit on order from TurboTweak since the XP pump is over 20yrs old and I've never put in a hot wire kit, but I'm not expecting this to be a fix since I'm not seeing any issues at the gauge.

The plugs look a nice light brown (I had them gapped @.032 I just squeezed them down to .024 but haven't driven it yet).
The car has a new ccci module and coilpack (tested ok caspers tester) wires are fairly new MSD 8.5mm.
Yes I'm seeing 2deg or so of retard on the scanmaster. No data logger yet, guess I might have to get one!
O2 volts are a nice ~780, compression tests 150+/- 2psi, I've pulled the valve covers and I'm not seeing a dead lobe (didn't measure just observed).

Lee
 
780...at what RPM?
Post your SM numbers with the engine warmed up.


780-820 in the 3-4000 rpm range
AF ~185
Int 128
BL 129

A bit difficult to get good readings since I'm staying out of the throttle and not recording
 
FYI.... Its pulling much smoother with the tighter gap on the plugs and I added a ground strap from the back of the ccci mod to the fire wall.
Not sure if that did anything but I figured it wouldn't hurt. I see lots of discussion about grounding.

I'm going to push it a little harder and dial the boost back up a bit and see if that gremlin stays away.
 
You're seeing KR, so I'd tell you not to push it...cuz it could be real. I'm asking for SM numbers warmed up, as you could have a high BLM count, which means you could have a vacuum leak or a pre-turbo exhaust leak, which would cause a lean condition and give the situation you're encountering. I always ran the stock Delco plugs from the GM Dealer, and had zero issues with them. 780 below max RPM makes me think it's running lean. Eric normally over fuels his chips to save us from ourselves. :) From all the files I've seen, if the owner has had Eric burn the chip for the exact combo and the boost the owner has specified, 780 would be lean at WOT on his default. I generally see 820's or around there on his default. I'm trying to save you from changing head gaskets.:)
 
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With the car in Park, I'm asking how fast the 02 numbers are moving. If slower than about 1 per second, then the 02 sensor is getting lazy and not reporting to the ECM correctly.
 
IilIRC: Pending the chip and revision, NB won't move in park if the chip is running in open loop. O2 will be locked.

I also recall warm idle BLM around 138+-5 if the car has breathers, and PVC installed. This ASSUMES the FP and MAF are correct (accurate).

Also seen pressure gauge calibration be off. Si. We combine that with operator reading error and 2-3 PSI is not uncommon which will seriously show as a high idle BLM.
 
BLM is fine. AF is around 4-6 at idle...so something is up. AF is airflow through the MAF. I need the numbers at idle in PARK.
 
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The AF I gave you earlier was in that 3-4000rpm range with a part throttle pull.
AF at idle is 5-6
The range on the O2 was 780-820 maybe 830 max definitely no lower than 780 -again I've been light on the throttle no SM not recording.
It is a newer TT chip and the O2 sensor is new too.
INT 128 @ idle
BLM 132 @ idle

Fuel pressure gauge is probably reasonably accurate since hood mounted and rail gauge read the same 38 @ idle with vac and 45 without vacuum.
 
Logging fuel pressure will show a psi swing and will only be visible on a log.

Are you experiencing an issue or just trying to understand?
 
Logging fuel pressure will show a psi swing and will only be visible on a log.

Are you experiencing an issue or just trying to understand?
Both!
I'm trying to determine if my fuel pressure looks ok at the gauge then can I eliminate fuel pump, wiring harness and filter from the list of suspects causing a part throttle stumble?
 
BLM is a tad high for my liking...a little lean. While you're waiting for the pump to arrive check for any pre-turbo exhaust leaks or vacuum leaks. Has the BLM always been 132, or has it changed recently.
 
Will do.
No BLM had been 128. I had been pulling and reconnecting vac lines but BLM should recover pretty quickly correct?
Drove it for a bit again today, all light throttle wet roads BLM's at 131
I haven't heard any exhaust leaks but I'll check closer.

It definitely drives better after closing the gap on the plugs to .024 from .032 and adding a ground strap to the back of the coil pack to the fire wall.
But I ain't holding my breath. I'm still babying it. When the weather dries up I'll commence with careful flogging.

Thanks again for your input
 
It's changed from 128...so something's up. Yes...it would have corrected fairly quick.
 
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