Losing Power in the Mountains

[davisca455]

Hi Folks,
The last couple of trips (not towing) to the Sierras our 'Burb has been losing power on the longer steeper climbs. The symptom is, that the engine tone changes (misses?) at full throttle when climbing. When I back off of the throttle just a hair, the miss clears up but will return as soon as I mat the pedal again. It doesn't occur in the lower altitude climbs. Maybe those climbs aren't as steep or as long? After noticing the power loss the first time, I changed the air and fuel filters for the next trip but there was no change in the symptom.

Simple Version:
Before the problem I could maintain 75mph on any climb. Now I have to back off the throttle to maintain 60-65mph.

Chris
'92 Suburban 4x4 (155,000mi)
3/4 Ton, 5.7L, 4L80E

 

[Molson02536]

Hi Folks,
The last couple of trips (not towing) to the Sierras our 'Burb has been losing power on the longer steeper climbs. The symptom is, that the engine tone changes (misses?) at full throttle when climbing. When I back off of the throttle just a hair, the miss clears up but will return as soon as I mat the pedal again. It doesn't occur in the lower altitude climbs. Maybe those climbs aren't as steep or as long? After noticing the power loss the first time, I changed the air and fuel filters for the next trip but there was no change in the symptom.

Simple Version:
Before the problem I could maintain 75mph on any climb. Now I have to back off the throttle to maintain 60-65mph.

Chris
'92 Suburban 4x4 (155,000mi)
3/4 Ton, 5.7L, 4L80E

Start with the simple and clean or replace your MAP sensor, the ECM takes readings from your MAP sensor to calculate the air fuel mixture after 75-80% of your throttle posotion.

Keep us posted and we can go from here, good luck.

 

[davisca455]

Excellent...I like simple.
Should I get the MAP sensor from the GM Dealer, or would one from Napa be allright?

 

[Molson02536]

Excellent...I like simple.
Should I get the MAP sensor from the GM Dealer, or would one from Napa be allright?

Napa is fine and you may want to also buy some throttle body cleaner and 2 cans of http://www.seafoamsales.com/ to clean out all the years of carbon build up in your engine.

Use half a can in your gas tank and the rest in your engine. This will dissolve carbon that is on your upper intake and valve stem. Take not that is you have never used Seafoam before, there will be extreme amount of white smoke from your tail pipe that will last as long as 10 min. So make sure you do it outside and not in your garage.

Good luck and keep us posted, read this post if you need more information on the Seafoam. http://gmcowners.com/gmc-forum/showthread.php?t=13770

 

[davisca455]

New MAP sensor installed and headed to the mountains on Friday. I'll report back with the results Friday night.
I did experience an "Unintended Consequence" while replacing the MAP sensor. When I touched the retaining clip on the MAP sensor connector, it just fell off. Has anyone else had any success replacing this connector housing? I currently have a creative array of Tie Wraps holding the connector in place.

 

[davisca455]

The performance of the 'Burb going up the Sierras this evening was WAY better after installing the new MAP sensor, but the engine was not 100% flawless. The symptom described in the 1st post still happened but not as frequently and not as drastic. Weird.

 

[Molson02536]

The performance of the 'Burb going up the Sierras this evening was WAY better after installing the new MAP sensor, but the engine was not 100% flawless. The symptom described in the 1st post still happened but not as frequently and not as drastic. Weird.

Did you try giving your Suburban the http://gmcowners.com/gmc-forum/showthread.php?t=13770. The Seafoam will clean out your upper intake and vacuum lines, and have you replaced the fuel filter??? the TBI was always fuel pressure sensitive

Glad your suburban is doing better now, but still room for improvement. Keep us posted.

 

[davisca455]

Replaced the fuel & air filters, no improvement.
Replaced the MAP sensor, big improvement.
Seafoam will be next.
If at all possible, I prefer to do one change at a time, so then I know what actually is the fix. We go up to the Sierras often enough that I won't have to wait long for results.

Thanks,
Chris

 

[davisca455]

Replaced the TPS last week.
Just completed the test drive up to the Sierras tis afternoon.
All power and then some has returned to the 'Burb.
Thanks Molson!

 

[john1989]

TBI / Engine Cleaner

This is interesting...our 89 has 190000 miles and still running strong. If we do this "clean-up" per say...loosing the carbon and all round gunk...will this make the old parts loose?
Help me!