5.7 wants to stall when stoped when HVAC is on

[SuperTramp]

+1 for replacing the spider injectors. I had an identical issue to yours (minus the CELs) and my truck would tend to intermittently die at red lights when the A/C was on. My little trick was to put the truck in neutral once the revs dipped instead of putting the truck in park. I replaced the CFI injectors to the upgraded MPFI injectors and the problem has not come back since.

Thanks for your suggestions. I used the same technique of putting transmission into "N" in order to keep the engine from shuddering. The use of Seafoam (only burnt 50% of the mixture) has helped some. I'll see if there are any changes once I get to "E". I'm considering adding fuel injector cleaner to see if this helps. I'm taking the "low hanging fruit" approach.

 

[SuperTramp]

I had those same codes on my K3500 with 5.7. I foolishly changed the O2 sensors, all 4 of them! That wasn't it. After weeks and weeks checking sensors with voltmeters and checking for vacuum leaks (on and off, since it's not a daily driver,) I bit the bullet and bought a scan tool with live data.

Looking at fuel trims on bank 2 (passenger side) and seeing a lean condition being the same at idle as revving up the engine I was 99% at that point it was injector problem, NOT the infamous intake manifold gasket leak, which is what I kept thinking it was. Next I did an injector balance test and #6 was stuck closed! Just to be certain I checked for injector pulse at said injector and it did have pulse.

Problem: Spider Injectors!

New MPFI assembly solved the problem. Good luck.

BTW, my SES light came and went on the dash, but the code was always stored when I had scanned it for codes before. So its more likely these were the issues, but maybe the ECU had not detected the lean code and that's why now the SES light is on. I doubt Seafoam did any good (or bad.)

Thanks for your suggestions. So, if I'm understanding correctly, are you suggesting I conduct an "injector balance test"? If so, is this typically a tool that can be rented from a local auto parts store?

 

[stutaeng]

You have a few options to do this test and I don't know of a parts store that rents these:

There's an OTC brand that is supposed to be really good, but not inexpensive: https://www.amazon.com/OTC-3398-Inj...ocphy=9026934&hvtargid=pla-490383844056&psc=1

There is another version, much more inexpensive. The guy at "Ratchets and Wrenches" on YT shows you how to use it and says it works well:
https://www.amazon.com/ALLOSUN-EM276-Fuel-Injector-Tester/dp/B0126MEK3C

Here's the scanner I bought. It's not a full-feature scanner (you have to spend at least $1,000 for something like that), but does perform injector balance test and has live data. You can get it cheaper with their on-line discounts: https://shop.advanceautoparts.com/p/innova-carscan-pro-5610/12071171-P?brandName=Innova

You also need a fuel pressure guage. Basically, the scanner primes the fuel pump and you record that number on the guage, then pulses the individual injector and record that number as well. Go one-by-one and they should drop around 5 psi after pulsing and they should be 1-2 psi of each other. I've posted links before on YT videos on how it's done. It's very easy. On my #6 injector, nothing happened, basically was dead.

Alternatively, look for a shop. May not be too expensive to diagnose. Not sure how much mechanic work you are willing to do yourself. Then it's about $250 for the MPFI injector assembly, if that's the problem. Or, just flip a coin and change that. Some guys recommend you replace it just because the original spider injectors are known to be glitchy. I did notice a MUCH smoother idle on mine when I changed them...

 

[96-2D-Hoe]

2) Am I correct in thinking that in order to check the ground at the pump, you either need a head of a small child or loosen the tank straps and lower the tank? When my pump went out, I have 30 gallons of gas in the tank. I ended up having to unbolt and slide the bed back. It was x#n?1!

You should know where the ground is already if you changed the pump If it was removed and replaced it should be fine.

I can't remember exactly but mine is it at the front of the tank and screwed into the frame or the chassis. It wasn't difficult to find. If you've never cleaned up the main grounds, battery to engine block front, block rear to frame and frame to firewall, that won't hurt either. Made a huge difference on mine and it's a SoCal truck with little to no corrosion.

 

[White96k2500]

UPDATE: (1998 k2500 5.7) The only thing I've had time to do to fix this problem is to add Seafoam to the gas tank. Within 10 miles, the SERVICE ENGINE light came on. Four days and 100 miles later, I checked the codes which were; "PO174 Bank 2 System too lean" and "PO154 Oxygen Circuit No Activity Detected (Bank 2 Sensor 1)". The system was reset and it hasn't thrown the codes again. The engine idle is smoother but still has room for improvement.

Does anyone have any interpretations of the codes and suggestions on what needs to be inspected and possible work that may need to be done? Has anyone ever experienced inaccurate codes sent by the computer?

Thank you in advance for your help.

I had something pop up on mine and say “no activity detected” can’t remember the code though, but upon further inspection the connector somehow came lose and was on the pass side exhaust and melted the connector.

 

[SuperTramp]

You have a few options to do this test and I don't know of a parts store that rents these:

There's an OTC brand that is supposed to be really good, but not inexpensive: https://www.amazon.com/OTC-3398-Inj...ocphy=9026934&hvtargid=pla-490383844056&psc=1

There is another version, much more inexpensive. The guy at "Ratchets and Wrenches" on YT shows you how to use it and says it works well:
https://www.amazon.com/ALLOSUN-EM276-Fuel-Injector-Tester/dp/B0126MEK3C

Here's the scanner I bought. It's not a full-feature scanner (you have to spend at least $1,000 for something like that), but does perform injector balance test and has live data. You can get it cheaper with their on-line discounts: https://shop.advanceautoparts.com/p/innova-carscan-pro-5610/12071171-P?brandName=Innova

You also need a fuel pressure guage. Basically, the scanner primes the fuel pump and you record that number on the guage, then pulses the individual injector and record that number as well. Go one-by-one and they should drop around 5 psi after pulsing and they should be 1-2 psi of each other. I've posted links before on YT videos on how it's done. It's very easy. On my #6 injector, nothing happened, basically was dead.

Alternatively, look for a shop. May not be too expensive to diagnose. Not sure how much mechanic work you are willing to do yourself. Then it's about $250 for the MPFI injector assembly, if that's the problem. Or, just flip a coin and change that. Some guys recommend you replace it just because the original spider injectors are known to be glitchy. I did notice a MUCH smoother idle on mine when I changed them...

Thanks Stutang. You've given me some good direction and I'll let you know what I've found when I get a free weekend to start

 

[SuperTramp]

You should know where the ground is already if you changed the pump If it was removed and replaced it should be fine.

I can't remember exactly but mine is it at the front of the tank and screwed into the frame or the chassis. It wasn't difficult to find. If you've never cleaned up the main grounds, battery to engine block front, block rear to frame and frame to firewall, that won't hurt either. Made a huge difference on mine and it's a SoCal truck with little to no corrosion.

96-2D-Hoe, Thanks for your comments and advice. I will check the grounds and I've been planning on performing a Big-3 upgrade so this could be good motivation to proceed. I'll let you know my results. I'm pretty certain I attached the fuel pump ground but will check this out as well.

 

[SuperTramp]

Here’s another clue to the problem. CHECK GAUGES light comes on and oil pressure drops. See picture

You must be registered for see images attach

You must be registered for see images attach

 

[SuperTramp]

Here’s a picture showing oil gauge under power

You must be registered for see images attach

 

[stutaeng]

Um, so it's either dropping oil pressure because of the low rpm( trying to stall) issue?

I don't think these trucks have something like a "low oil pressure shut off" mechanism. Basically, you can run the engine on low oil pressure until it locks up. I know I drove my truck with low oil pressure with the switch disconnected and mechanical guage hooked up for like 2 weeks middle of summer last year. In my case it was a real low oil pressure problem, so I had to switch to a heavy oil just to buy me more time...

Besides what we have recommended, you should also check oil pressure with a mechanical guage. The oil pressure sender is behind the distributor and you need a special socket.

So this happens only with the HVAC on? The cold or heater? Both? Maybe you have a huge draw and that's what's trying to happen? But I think you would blown a fuse in that case?

What a puzzle to solve!