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Old 06-17-2022, 02:09 PM   #1
DavePolyakov
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Default After pull runs lean and crappy

1990 740 Turbo lh2.4

Did a 0-60 pull at 12psi afr's were normal this was about two hours into my doordash shift and it was boosting nicely. Upon slowing down, it began to run lean, hesitating, and low power from a stop. Afr's in the 16-17 range, drove home like this 2 miles, and stayed out of boost. At idle it may return to normal or even go rich. Upon any accelerator input, it will begin running lean. I checked all hose connections, the car has a new fuel filter, I recently used a fuel cleaning agent, a new o2 sensor, spark plugs and wires are all newish. Doesn't sound like it's misfiring. Disconnecting AMM makes it run like a car without the AMM connected. I understand this is probably a common issue, I just could use some guidance. Thanks. Also, I would love to hear from someone about how to monitor fuel pressure on a car without a Schrader valve on the fuel rail.
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Old 06-17-2022, 02:47 PM   #2
esmth
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This is exactly what happened to me when I got stranded 150 miles away from home after a night of street fun/heavy boosting with my car. The maf took a dump the next morning and the car would run too lean. I was able to get home without the maf plugged in and now I keep always a good spare in the car.
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Old 06-17-2022, 03:17 PM   #3
bobxyz
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Check your hoses again - make sure they're all fully seated (including brake booster, and IAC hoses), and that there aren't any new ruptures/big cracks (squeeze and feel around the backsides where you can't see it easily). You might also clean your MAF (use MAF cleaner, not something too harsh like brake or carb cleaner).
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Old 06-17-2022, 05:01 PM   #4
rb92673
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Quote:
Originally Posted by DavePolyakov View Post
1990 740 Turbo lh2.4
Also, I would love to hear from someone about how to monitor fuel pressure on a car without a Schrader valve on the fuel rail.
I used a banjo adapter for a Cummins at the fuel filter and a cheap ebay pressure sensor to connect to microsquirt to log fuel pressures.

https://www.glowshiftdirect.com/fuel...valve-cummins/

You could connect it to an electronic gauge instead.
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Old 06-17-2022, 08:36 PM   #5
DavePolyakov
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I removed the screens and sprayed a good 10-15 sprays in the MAF with CRC MAF cleaner put it back and the car only starts and runs for 3 seconds. Completely destroyed it even though it was already compromised. I have a spare MAF that I put in and it idles perfectly normal, going on a drive in just a moment. Should I keep a spare MAF in my car? I don't like how it failed me, luckily I was close to home.
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Old 06-17-2022, 09:18 PM   #6
bobxyz
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Sorry, didn't mean to make it worse.

If you look inside the old MAF, there should be 4 spikes sticking out in roughly a square. Between 3 of the 4 should be a really thin and hard to see wire (or at least that's what a LH2.4 MAF has). You may need to try a few different backgrounds to see the wire. If you can see it, is it intact or is it broken somewhere? Maybe tapping it with a fingernail while watching will show the break.
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Old 06-18-2022, 12:18 PM   #7
dl242gt
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When the mass air sensor failed on my wagon it was sudden. It would let the car start but it would miss and run crappy for just a few seconds and then stall. A good used sensor sorted it right out. No codes either.
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