Map sensor

[Hagar1]

So, I pulled the intake off my 5.7 the other day and after re-installing it, I have a p0128 code and I have the throttle body symbol with the lightning bolt through it illuminated. Didn't touch either one when I had the manifold off. Then there was a c121c code at one time as well but it cleared when I erased the codes. So I'm only showing the map code and the throttle body symbol.
Any ideas / suggestions?
One other thing, the vacuum shows change on the diagnostic box but the voltage stays at 4.99.
I swapped in a spare Map sensor and nothing changed.

 

[DripJust]

That happened to me also when I ported my intake changed the gaskets. After trying to clear the DTC and running through a few drive cycles the issue went back to normal.

 

[Hagar1]

That happened to me also when I ported my intake changed the gaskets. After trying to clear the DTC and running through a few drive cycles the issue went back to normal.

Thank you! I'll give that a try.
Guess my truck is just a Chris ......... Not a Christine.

 

[Hagar1]

That happened to me also when I ported my intake changed the gaskets. After trying to clear the DTC and running through a few drive cycles the issue went back to normal.

Did you have the light for the throttle illuminated as well?

 

[DripJust]

Did you have the light for the throttle illuminated as well?

Yes I did.

 

[Hagar1]

Yes I did.

Roughly how long did it take to resolve? Thanks!

 

[Wild one]

Did you pull the negative battery cable off before removing the throttle body,it's usually wise to do that anytime you remove the TB.What happens if you hard reset it with a battery disconnect?

 

[Hagar1]

Yes I did.

It resolved itself after a few minutes of key on time. Thanks

 

[Hagar1]

Did you pull the negative battery cable off before removing the throttle body,it's usually wise to do that anytime you remove the TB.What happens if you hard reset it with a battery disconnect?

Yes I did. I'm "old school" with a lot of things and disconnecting battery is on the top of the list both for personal safety and electronics. I once worked with a guy who shorted the battery to ground with his watch bracelet. He didn't do it a second time. I also did a reset on pcm. It resolved itself, I think it falls into the PFM category.

 

[Hagar1]

Did you pull the negative battery cable off before removing the throttle body,it's usually wise to do that anytime you remove the TB.What happens if you hard reset it with a battery disconnect?

Truck runs better but I still have a puzzle .... engine vacuum drops to zero under the slightest load. Far beyond where it should go in those conditions. If I down shift to 3rd at 80 kph, it shows decent vacuum. That is how it should work but in regular "drive" vacuum really drops. I've checked the cam operation and it responds as it should.
If it was an older vehicle with a distributor, I'd take a look at timing. It sort of feels like late timing, but how, is beyond me.
Any ideas?

 

[Wild one]

Truck runs better but I still have a puzzle .... engine vacuum drops to zero under the slightest load. Far beyond where it should go in those conditions. If I down shift to 3rd at 80 kph, it shows decent vacuum. That is how it should work but in regular "drive" vacuum really drops. I've checked the cam operation and it responds as it should.
If it was an older vehicle with a distributor, I'd take a look at timing. It sort of feels like late timing, but how, is beyond me.
Any ideas?

Hook a real vacumn gauge to it via the brake booster hose and see what you get.It'll drop if you go to WOT at lower engine speeds,but it shouldn't drop to 0

 

[Hagar1]

Hook a real vacumn gauge to it via the brake booster hose and see what you get.It'll drop if you go to WOT at lower engine speeds,but it shouldn't drop to 0

I already did that, it is how I caught the bad intake seals. 6 out of 8 were leaking as it turned out. I'm running about 20" vac at idle in neutral and about 17 - 18 in drive. Touch the throttle to drive away and drops to about 2 - 3 " hg. Cruising at 80 kph, vacuum is low and any even slight incline even one degree, the vacuum drops to zero. I use to be pretty good at this stuff but time, age, and memory I guess have taken their toll. The vacuum is steady, not bouncing around.

 

[Wild one]

I already did that, it is how I caught the bad intake seals. 6 out of 8 were leaking as it turned out. I'm running about 20" vac at idle in neutral and about 17 - 18 in drive. Touch the throttle to drive away and drops to about 2 - 3 " hg. Cruising at 80 kph, vacuum is low and any even slight incline even one degree, the vacuum drops to zero. I use to be pretty good at this stuff but time, age, and memory I guess have taken their toll. The vacuum is steady, not bouncing around.

Is it running good,if it is i wouldn't worry to much about it. You could take some starting fluid/etc,and spray it around the manifold to check for vacumn leaks.There are a few reports of cracked manifolds,but it's not a very common issue

 

[Hagar1]

I just finished replacing the manifold seals, torqued the bolts to 108 inch lb. It is running "decent" but, it went from 22 - 23 mpg down to around 10, literally over night. The fuel consumption, I believe, is directly related to the vacuum issue because with low manifold vacuum, the MAP output voltage is higher and that is a significant "player" along with other inputs towards fuel economy. This thing is so bad that the back bumper and the back fender in the tailpipe area are all blackened.

It sort of feels like the engine is "under load" like you are pulling a trailer. I check the transmission operation, it shift as it should, when it should and I can see the convertor seems to be functioning properly.