vacuum problem?
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Freshman User
Joined: Sep 2010
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vacuum problem?
Alright, I've got a 89 250 351/c6 4x4. My concern is that I have low Vacuum pressure. I my trans has a lazy shift to 3rd with a brand new modulator. and think it might be due to low pressure I measured it at 16lbs from the upper plenum at idle (650rmp or so) and as i gave it throttle it would go up to about 19lbs is this (to spec)?
PS the truck likes to stall right after a cold start without some pedal is usually fine after about 1 minute though. I suspect this might be related to a possibly low vacuum maybe? the stalling isn't really my concern just thought the info might help.
PS the truck likes to stall right after a cold start without some pedal is usually fine after about 1 minute though. I suspect this might be related to a possibly low vacuum maybe? the stalling isn't really my concern just thought the info might help.
Cargo Master
Joined: Apr 2003
Posts: 2,408
Likes: 5
From: Parkesburg PA
How many miles do you have?
Also is the ready steady or does it fluctuate? If it fluctuates, by how much?
It's normal for the gauge to read higher when you rev it quick. It should return to your baseline after a quick bit.
Also is the ready steady or does it fluctuate? If it fluctuates, by how much?
It's normal for the gauge to read higher when you rev it quick. It should return to your baseline after a quick bit.
Fleet Mechanic
Joined: Jun 2011
Posts: 1,324
Likes: 3
From: Conway, South Carolina
How about pull the vacuum line off the modulator and stick your finger over it. Your vacuum line might be cracked. Also if you gas the engine, Like floor it, you should lose vacuum, then it should come back.
Fleet Owner
Joined: Oct 2005
Posts: 20,780
Likes: 1,746
From: Kentucky
Your vacuum levels sound about right. I do not think that has anything to do with your transmission issue. Has the transmission always exhibited this behavior? Have you checked the transmission fluid level? When was the last time you changed the fluid and filter?
What are the numerical codes and when they were displayed? i.e. during the KOEO tests, KOER or CM?
The stalling during a cold start is more than likely caused by a dirty or faulty IAC (IAB). Here is some info on this piece: Fuel Injection Technical Library » Idle Air Bypass (IAB)
What are the numerical codes and when they were displayed? i.e. during the KOEO tests, KOER or CM?
The stalling during a cold start is more than likely caused by a dirty or faulty IAC (IAB). Here is some info on this piece: Fuel Injection Technical Library » Idle Air Bypass (IAB)
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Freshman User
Joined: Sep 2010
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so i read up on iacv and when i unplug it the truck stalls but i took it apart and cleaned it and put on a new gasket still stalls... so no luck there. the fluid levels are good just rechecked but fluid and filter where changed about 1000 miles ago.
The code numbers are 22 and 23 one is tps out of range and the other is map out of range thoughts?
The code numbers are 22 and 23 one is tps out of range and the other is map out of range thoughts?
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