Low pressure all of a sudden

[Scottydoggs]

I use sea foam in the oil all of the time. Was very successful at getting rid of lifter tick in more than one vehicle. It is a recommended use on the can, however you are only supposed to use a few ounces and for just a few hundred miles right before oil change. Read the label and use accordingly.

ive heard more lost oil pressure and now its knocking storys then i care to talk about when seafoam in used in the oil. its always when they drive it vs letting it idle for 15 minutes and doing a oil change. iirc s/f says to drive it a few hundred miles, and iirc they call for a third the bottle in the gas tank, third in the crank case, and a third in the brake booster line.

in this case he clearly used to much in the oil. just hope the pressure comes back.

there is a screen under the o/p sensor, it just might be clogged up good now blocking oil to the sensor. thus it reading low now. if you take that o/p sensor out, you can screw a mechanical pressure gauge in to it and fire it up and get more accurate reading of the pressure.

 

[iamdub]

Boy that Seafoam is awesome trouble. Thanks for the story Tim and welcome! You'll love it here.

I couldn't wait until I got off work so I ran home at lunch after stopping at the parts store to grab some MAFS cleaner.

I took it off and cleaned it out really well, let it dry and hit it again. I put it back in, connected the battery and started it up. It ran perfectly with 42psi oil pressure like it did before and I thought, "OMG! That was it!" Then after 20 seconds it immediately (not gradually) went back to running like shit again... I went ahead and cleared the codes and start it again. It ran really rough like it was about to die for about 45 seconds but I didn't get an engine light. My next option is to replace the MAFS tonight. I bought one while at the store so I'll throw that in and we'll try again. I'm not hearing anything knocking in the engine other than it just sounds like it's starving or being flooded with gas.

Could the ignition security system have anything to do this? As I said before, I replaced the factory stereo last weekend and it only worked correctly for about 1 day before I started having issues with it rebooting constantly. I wasn't having engine issues until yesterday. Just a stab in the dark. Thanks again all!

It's worth a shot to disconnect the radio to at least rule that out. Just unplug the whole connector either from the back of the radio or separate your adapter harness. It sounds like the only data interface you tapped in to was the one for the SWC, and I don't see how that would have any effect on your other symptoms. It's worth unplugging everything, though.

As far as it running perfect then not, it could have been because it was in open loop. The PCM ignores input from certain sensors until specific parameters (minimal coolant temperature, run time, oxygen sensor temp, etc.) are met. I didn't think the MAF was included, but it may be. You can unplug it and see if it runs good again.

After that 20 seconds of running perfect and 45psi oil pressure, when it immediately started "running like shit again", what did the oil pressure do? Did it just drop low because of the low engine RPM or did it bottom out at 0?

Did you only put Seafoam in the crankcase, none through a vacuum line or anything? I'm wondering if the MAP or an O2 sensor was damaged somehow. AFAIK, Seafoam is safe for O2 sensors, but if it breaks up stuff and that ends up clogging a sensor or cat, that could cause issues. But, the only way Seafoam in the crankcase could affect what's coming out the exhaust is if the alcohol fumes made it through the PCV system then into the intake manifold. That's quite a farfetched scenario, but a whole can of Seafoam in the oil is a strong dose. Do you have, or have access to a scanner that can show a live data stream?

 

[jeffsyukon]

Check your vacuum lines and make sure one didnt come disconnected or damaged. I recently had a crack develop in the PCV line near the back of the driver side valve cover. The truck stalled and ran like hot garbage until I fixed the vac line.

Sent from my SM-G965U using Tapatalk

 

[HiHoeSilver]

ive heard more lost oil pressure and now its knocking storys then i care to talk about when seafoam in used in the oil. its always when they drive it vs letting it idle for 15 minutes and doing a oil change. iirc s/f says to drive it a few hundred miles, and iirc they call for a third the bottle in the gas tank, third in the crank case, and a third in the brake booster line.

in this case he clearly used to much in the oil. just hope the pressure comes back.

there is a screen under the o/p sensor, it just might be clogged up good now blocking oil to the sensor. thus it reading low now. if you take that o/p sensor out, you can screw a mechanical pressure gauge in to it and fire it up and get more accurate reading of the pressure.

NBS. I'm pretty sure there's not a screen. My understanding is that they added that with the implementation of AFM. Am I wrong?

As far as it running perfect then not, it could have been because it was in open loop. The PCM ignores input from certain sensors until specific parameters (minimal coolant temperature, run time, oxygen sensor temp, etc.) are met. I didn't think the MAF was included, but it may be. You can unplug it and see if it runs good again.

After that 20 seconds of running perfect and 45psi oil pressure, when it immediately started "running like shit again", what did the oil pressure do? Did it just drop low because of the low engine RPM or did it bottom out at 0?

Do you have, or have access to a scanner that can show a live data stream?

This.

 

[OR VietVet]

NBS. I'm pretty sure there's not a screen. My understanding is that they added that with the implementation of AFM. Am I wrong?



This.

Last I saw on here the screen did not start till the AFM. I saw that in a thread here. I am a 2002 so I would not know for sure except for what I saw here.

 

[dnt1010]

Fascinating thread. I know that my engine is sludged a bit but after reading this it wil stay sludged LOL no engine cleaning for me.

 

[mijohnst]

I agree with DNT1010... I'll never do this again. lol

Progress report!

I disconnected the new stereo when I got home tonight to eliminate that. I tried starting the Tahoe and like before it was really rough. Like it was before and would run for 10-15 seconds and then die. At one point I got the RPM's up to about 3k and was stable, I just held it there for about 2 minutes hoping it would burn away whatever it was causing the problem. When I let off the gas it would go back to running rough and then die.

The next thing I did was install the new MAF that I bought from Napa. I got in the car and it started right up and ran normally! Idle was about 800rpm and no missing. Still, no oil pressure. I'm not starting to think that's the sensor is bad so that'll get replaced tomorrow. I let it run for a few minutes and turned it off and ran the codes on it. No more MAF codes! So I guess I did have a bad MAF. IAMDUB was right on! While it was running I sprayed starter fluid around the intake and any vacuum hose I could find and the engine didn't change at all.

I think I'm home free and thinking about how I'm going to come back here and tell you all about it but before I do I run/clearing the codes one last time. I tried to start the engine now it cranks but won't turn over. Ugg... I let it sit for 10 minutes and try again. It starts and sounds normal again. It runs for about 30 seconds and just stops. So now it cranks but it won't turn over. I had this problem in my Yukon last summer and it was the ignition switch. I happen to have a spare so I switched it out but it still won't turn over. I can't tell if I'm getting closer or further from fixing this.

I went from having no issues to a whole bunch in a matter of 2 days. Thanks for everyone posting in this thread! This will surely help others down the road.

 

[OR VietVet]

I agree with DNT1010... I'll never do this again. lol

Progress report!

I disconnected the new stereo when I got home tonight to eliminate that. I tried starting the Tahoe and like before it was really rough. Like it was before and would run for 10-15 seconds and then die. At one point I got the RPM's up to about 3k and was stable, I just held it there for about 2 minutes hoping it would burn away whatever it was causing the problem. When I let off the gas it would go back to running rough and then die.

The next thing I did was install the new MAF that I bought from Napa. I got in the car and it started right up and ran normally! Idle was about 800rpm and no missing. Still, no oil pressure. I'm not starting to think that's the sensor is bad so that'll get replaced tomorrow. I let it run for a few minutes and turned it off and ran the codes on it. No more MAF codes! So I guess I did have a bad MAF. IAMDUB was right on! While it was running I sprayed starter fluid around the intake and any vacuum hose I could find and the engine didn't change at all.

I think I'm home free and thinking about how I'm going to come back here and tell you all about it but before I do I run/clearing the codes one last time. I tried to start the engine now it cranks but won't turn over. Ugg... I let it sit for 10 minutes and try again. It starts and sounds normal again. It runs for about 30 seconds and just stops. So now it cranks but it won't turn over. I had this problem in my Yukon last summer and it was the ignition switch. I happen to have a spare so I switched it out but it still won't turn over. I can't tell if I'm getting closer or further from fixing this.

I went from having no issues to a whole bunch in a matter of 2 days. Thanks for everyone posting in this thread! This will surely help others down the road.

I just want to address one statement. When you say it cranks but will not turn over you are talking about one in the same. Cranking engine IS turning over. Cranking engine and then starts or fires off and turning engine over and starts or fires off, is the same. I know you meant not starting but in this world, cranking and turning over are the SAME. No crank is no engine spin. No turn over is no engine spin. It seems I am rubbing salt into the wounds with all your problems but had to say it. I sure want to know what the fuel pressure is when you have a gauge attached and just turn the key on with engine off. I then want to know what the fuel pressure is f you see pressure when you do that and then tell us if the pressure bleeds off when you turn the key off. Then we want to know what fuel pressure is when you crank the engine and it then starts and runs at idle and then, f it stays running we want to know what the pressure is at 1000 rpm and 1500 rpm and 2000 rpm and a snap throttle. Maybe an ignition switch but who knows but does not sound like it. Just for giggles, turn key on but do not crank the engine and shift in to neutral and then try to crank engine and see if it starts and stays running. Go thru the same procedures you just did when you seemed to think all was fixed but this time do it all in neutral when you try to crank and start the engine.

 

[mijohnst]

I just want to address one statement. When you say it cranks but will not turn over you are talking about one in the same. Cranking engine IS turning over. Cranking engine and then starts or fires off and turning engine over and starts or fires off, is the same. I know you meant not starting but in this world, cranking and turning over are the SAME. No crank is no engine spin. No turn over is no engine spin. It seems I am rubbing salt into the wounds with all your problems but had to say it. I sure want to know what the fuel pressure is when you have a gauge attached and just turn the key on with engine off. I then want to know what the fuel pressure is f you see pressure when you do that and then tell us if the pressure bleeds off when you turn the key off. Then we want to know what fuel pressure is when you crank the engine and it then starts and runs at idle and then, f it stays running we want to know what the pressure is at 1000 rpm and 1500 rpm and 2000 rpm and a snap throttle. Maybe an ignition switch but who knows but does not sound like it. Just for giggles, turn key on but do not crank the engine and shift in to neutral and then try to crank engine and see if it starts and stays running. Go thru the same procedures you just did when you seemed to think all was fixed but this time do it all in neutral when you try to crank and start the engine.

Thanks for pointing that out to me. I can see where that could be confusing for someone. The starter turns the engine but it won't roll over into the engine running is what I should have said.

So that's one thing that I left out before. I didn't think it was a fuel problem but I tested out the pressure anyway and while it's idling it's above 60psi. I didn't test it the different RPM's but I will tomorrow if I can get one of my kids to hold it for me while I watch the gauge. I think that 60psi sounds pretty good since my Yukon has a new fuel pump and runs at about 50psi and has no issues. Thanks for the suggestions!

 

[HiHoeSilver]

Thanks for pointing that out to me. I can see where that could be confusing for someone. The starter turns the engine but it won't roll over into the engine running is what I should have said.

So that's one thing that I left out before. I didn't think it was a fuel problem but I tested out the pressure anyway and while it's idling it's above 60psi. I didn't test it the different RPM's but I will tomorrow if I can get one of my kids to hold it for me while I watch the gauge. I think that 60psi sounds pretty good since my Yukon has a new fuel pump and runs at about 50psi and has no issues. Thanks for the suggestions!

Twice you have cleaned or replaced the MAF and it ran normally. For a time. You said 20 seconds the first time (after cleaning). Until you shut it off the second (after replacing)?

You said no codes when it ran. Any codes now? Did you mess around with the harness at all like Chris said?