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Old 06-13-2014, 04:13 AM   #1
quillc
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Default Random Lean Condition

I have recently been having a random lean condition. I suspect a bad lift pump (pre pump/transfer pump, whatever you want to call it).

The car:
1983 242DL. NA car.
B23F high compression. slightly milled for a head cleanup back when. Likely around 10.5:1. Knocks on regular unleaded (I run premium all the time).
A cam, 2.5deg advanced with an IPD old school cam gear and a Kevlar belt.
Stahl header.
2.5" exhaust with a Flowmaster resonator and Super 50 muffler.
Stock LH2.

Last week, I was on the highway and it suddenly bogged heavily and smelled strongly of fuel. After that it would miss and bog randomly.

I replaced the AMM (reman unit). It seemed to drive better. The symptoms returned however.
I replaced the FPR (twice) with known good units (first time with a 3.0 bar, second time with a 2.5 bar)
I replaced the O2 sensor. The wiring harness is an updated unit, so I went a got a heater sensor from LH2.2.
I replaced the fuel filter.
I installed an AEM wideband sensor (I had it on hand so why not).
I swapped to another computer.

When the car bogs, the AFR is quite high (often 18 or higher). Definitely a fuel delivery condition.

Today, I replaced the main fuel pump with a known good pump (as well as using a new Bosch filter), cleaned the grounds and checked the fuel pump connections. On my test drive, the problem occurred a couple of times.

The lift pump is only 25,000 miles old. At this point, its really the only thing left that I can think of. When I replaced the fuel filter (and later swapped the main pump) there was a substantial amount of sediment that came out. I have a spare tank with a known good lift pump in it that I am thinking about swapping in this weekend. The installed tank has a substantial dent in the bottom from the PO's idiocy.

The lean condition appears to happen randomly.

Your thoughts?
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Old 06-13-2014, 07:55 PM   #2
Three Fat Tigers
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Never seen any sediment when pulling any Volvo fuel filter, so that could be it, upstream. I think I would pull the filter, run the hose into a bucket and jumper the fuse for the rear pump to see if the pump is putting out any debris or obvious fluctuations. I might also try to test voltage at an injector connector, rigged so you can read it from inside the car during an event, just to be sure it's not a voltage issue; not sure if they are switched by relay, but if from the ignition switch, those can fail in odd ways.

My '84 245 had and adjust screw on the MAF sensor, I recall when my ran lean I just played with that and it took care of it. I had got about 34 MPG on a trip up north, though overheated and killed the cat, which eventually plugged up on me later on.
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Old 06-14-2014, 09:42 AM   #3
cleanflametrap
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Quote:
Originally Posted by quillc View Post
I have recently been having a random lean condition. I suspect a bad lift pump (pre pump/transfer pump, whatever you want to call it).
Could be, I suppose, but the pump itself is not the only part that fails when it does not do its job of providing the main pump with fuel. Diagnostics are simple when you can reliably enjoy the symptom, but this randomness needs more description.
Quote:
Originally Posted by quillc View Post
I replaced the AMM (reman unit). It seemed to drive better. The symptoms returned however.
Why do you suppose it was temporarily "fixed"?
Quote:
Originally Posted by quillc View Post
When the car bogs, the AFR is quite high (often 18 or higher). Definitely a fuel delivery condition.
And you smell fuel??
Quote:
Originally Posted by quillc View Post
Today, I replaced the main fuel pump with a known good pump (as well as using a new Bosch filter)...
Known good? I know they wear, but during that wear process the car keeps running "fine" until something like the lift pump stops providing fuel input, or a lousy 25A fuse socket drops the voltage available at the brushes.
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The lift pump is only 25,000 miles old.
I've experienced lift pump failure in a lot fewer miles. In the Tank Guessing you've already read this though.
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Originally Posted by quillc View Post
known good lift pump
Known good? Then you must know how to verify yours.
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Originally Posted by quillc View Post
Your thoughts?
Ignition?
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Old 06-16-2014, 04:54 PM   #4
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Drove it to work on Friday (67 miles each way).

Turns out to have been a sticking injector(s).

They would randomly stick open (smell fuel and AFR would be pegged low) and randomly stick closed (lean AFR pegged high).

Pulled over and bought some fuel system cleaner. Was immediately much better. Still happening (lean), but frequency is much reduced. Stopped sticking open entirely immediately, with them sticking closed occasionally (10% or so) after decal. If I rev the engine, they will un-stick. I am having a replacement set of injectors cleaned (Dr. Injector here locally) and will R/R them this week.

Funny thing is that I only run premium gas from Costco. They put tons of extra fuel system cleaner in their fuel. I used to run Lucas fuel additive, but stopped about 6 months ago as I figured it was overkill. I never head a problem when I was running the Lucas product. Same injectors for a couple of years. Could be a coincidence, but I'm of the opinion that its the ethanol.
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Old 06-19-2014, 04:08 PM   #5
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Got a set of my spare injectors (orange tops Bosch 0 280 150 209) cleaned at Dr. Injector in Tacoma and popped them in yesterday.

Dramatic difference.

AFRs were hovering in the 12-13 range. They would get up into the 14-15 range under full throttle/high load conditions. The AFRs would randomly peg in either direction as the injector(s) stuck open or closed.

With the refreshed injectors, the AFRs are hovering in the 14.4-15.2 under pretty much all conditions. Idles like a new car (or at least one with an A cam in it anyway). I'm sure it will get dramatically better fuel economy as well of course.
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