1999 Chev Astro 4.3l low power under load

Working on the above mentioned vehicle. Here's my steps taken to get to where I'm at:

Test drive to confirm low power, falls on its face wot. Idles fine, starts fine, low throttle angle driving you don't really notice any concerns.

Connect Fuel pressure gauge and test drive again. Fuel pressure prime 65 PSI, Idle 52 PSI, WOT 60 PSI.(I checked that's pretty well in the specs)

WOT B1S1/B2S1 flat line lean MAF at 62 g/s. MAF at Idle was about 5 g/s, on a 4.3l veh I thought was about normal so didn't give to much focus to the MAF

Scoped the injector voltages and under load the voltage spikes dropped from around 100v to 20v. I've done this same testing on other port injected chev's and replaced the fuel spider thus correcting the low power demand. Short story, replaced the spider in this Astro and it is running the same.

Hopefully I can get some help finding what I'm missing. Thanks. Brent @ Gear Head Garage

I'd attach the scan data but need some time to load the shop key on my lap top and figure out that process.

62 g/ s at w.o.t on a 4.3 is way to low. it should be around 130 thats what ive always seen when working on the 4.3.

Was this 62 grams taken on test drive wot or just no load wot?

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during the test drive. 1st gear wot run.

in that case its way low. did b1s1 and b2s1 both stay lean during wot?

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I posted a PID screen I took recently. MAF sensor fixed it. I test drove without the scanner hooked up first and it ran well with the new MAF sensor, the van blew a rad hose so will fix that and get the after data and post on here. Thanks.

No worries I asked because a plugged cat can cause the low maf reading as well . but as I think of it that van probably only has 1 cat after the y pipe so it wouldn't make a difference . Many manufactures have great maf backup strategy (looking at you toyota...) and when dealing with a low maf the easiest verification is do disconnect it and drive it and see if you get full power back if not then you would start suspecting a plugged exhaust which you can use a vacuum gauge on the intake or the map sensor to diagnose that . Also I have a write up somewhere down the list in the tools and techniques section that describes what you should expect to see on your maf for different sized engine that will aid in diagnosing bad mafs. I'll dig up a link if you want to read it but can't find it

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I'd like to see that MAF readings page you've got. Here's the after repair data, is there any way to upload a shopstream file? I'll just the print screen again. A plugged cat would likely show rich O2 readings.

forum/diagnostic-tools-and-techniques/2587-known-good-pids.htm



I see your peaking at 125 which is a little low taking a look at your load pid will also help determine if your running for all it's potential (should be able to reach 100%) if it runs well I wouldn't sweat the low maf reading it just may be misreporting or have some other issues down the road (air leaks upstream of maf can cause a low reading ) another (sometimes easy) test is to remove upstream oxygen sensor from exhaust and see if your maf reading raises . I expect to see around 150 grams when everything is in good condition

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brentoximous wrote: Here's the after repair data, is there any way to upload a shopstream file?

Unfortunately not. I'd love to be able to, but the forums won't have it. I'm a big fan of ScanShare.io for data sharing, or good ol' file drop sites.