Chevy Express 3500 van struggles while towing
July 13th, 2019, 12:21 PM
#11
CF Senior Member
With the 6.0 you should have not trouble at all regardless of elevation. It should pull with little effort. Something is wrong that needs to be figured out.
July 13th, 2019, 1:24 PM
#12
On a normally aspirated engine, the MAP measures intake manifold pressure, which will be either at atmospheric pressure or below (a vacuum). It is an indication of engine load. The 'M' literally stands for manifold. There is a different sensor for measuring the ambient barometric pressure.
The MAF measures the mass of incoming air (probably many times per second), so that it can add the appropriate amount of fuel for efficient combustion. That means that if you're driving around Leadville, CO at 10,000ft , the MAF will measure lower air mass and decrease the fuel mixture.
Wiki says
"A typical naturally aspirated engine configuration employs one or the other"
and
"The MAP sensor can also be used in OBD II applications to test the EGR (exhaust gas recirculation) valve for functionality, an application typical in OBD II equipped General Motors engines."
Last edited by mountainmanjoe; July 13th, 2019 at 1:42 PM.
July 13th, 2019, 4:10 PM
#13
CF Beginner
Thread Starter
Join Date: Jul 2019
Posts: 8
Likes: 0
Received 0 Likes
on
0 Posts
Looked up the specs with the VIN decoder today...6.0L with a 3.73 rear axel ratio.
I too think I shouldn't have any issue pulling with this van. How can I diagnose this?
I too think I shouldn't have any issue pulling with this van. How can I diagnose this?
July 13th, 2019, 6:40 PM
#14
Check the easy stuff like fuel pressure and ignition yourself. After that a mechanic who can diagnose OBD data
July 14th, 2019, 1:54 PM
#15
CF Senior Member
Check your air filter. Change any fluids/filters that need changing, service the transmission, replace differential fluid, check spark plugs. I had a fuel system service/cleaning done on mine last year.. helped clear up some sluggishness.
July 15th, 2019, 12:24 AM
#16
No, I meant MAF.
On a normally aspirated engine, the MAP measures intake manifold pressure, which will be either at atmospheric pressure or below (a vacuum). It is an indication of engine load. The 'M' literally stands for manifold. There is a different sensor for measuring the ambient barometric pressure.
The MAF measures the mass of incoming air (probably many times per second), so that it can add the appropriate amount of fuel for efficient combustion. That means that if you're driving around Leadville, CO at 10,000ft , the MAF will measure lower air mass and decrease the fuel mixture.
more important on the next gen without a vacuum fpr.
Wiki says
"A typical naturally aspirated engine configuration employs one or the other"
and
"The MAP sensor can also be used in OBD II applications to test the EGR (exhaust gas recirculation) valve for functionality, an application typical in OBD II equipped General Motors engines."
On a normally aspirated engine, the MAP measures intake manifold pressure, which will be either at atmospheric pressure or below (a vacuum). It is an indication of engine load. The 'M' literally stands for manifold. There is a different sensor for measuring the ambient barometric pressure.
The MAF measures the mass of incoming air (probably many times per second), so that it can add the appropriate amount of fuel for efficient combustion. That means that if you're driving around Leadville, CO at 10,000ft , the MAF will measure lower air mass and decrease the fuel mixture.
more important on the next gen without a vacuum fpr.
Wiki says
"A typical naturally aspirated engine configuration employs one or the other"
and
"The MAP sensor can also be used in OBD II applications to test the EGR (exhaust gas recirculation) valve for functionality, an application typical in OBD II equipped General Motors engines."
Last edited by tech2; July 15th, 2019 at 12:28 AM.
July 15th, 2019, 2:28 AM
#17
I did some more reading in the GM documents. The PCM indeed uses MAP input to determine air/fuel ratio. But it sounds like MAP input is used to decide if the engine is undergoing acceleration/deceleration etc. , and not so much measuring the amount of air coming in. For example, rich mixture helps reduce hesitation when flooring it.
Injector fuel pressure is pretty constant. Only the spray duration is varied. In closed-loop operation the PCM uses mainly HO2S sensors for fuel trim. In fact the diagnostic procedure for lack of power makes no mention of MAP.
Injector fuel pressure is pretty constant. Only the spray duration is varied. In closed-loop operation the PCM uses mainly HO2S sensors for fuel trim. In fact the diagnostic procedure for lack of power makes no mention of MAP.
July 15th, 2019, 8:26 AM
#18
map in this instance is used in a calculation adjustment for fuel metering...on returnless fuel systems the fpr isn't vacuum operated so the pcm needs to know map for the correction factor. to overcome spraying fuel into a vacuum vs pressure the pcm must up injector on time. What changes on accell/decell...pressure in the manifold due to throttle opening and barometric pressure.
Last edited by tech2; July 15th, 2019 at 8:28 AM.
The following users liked this post:
diesel72 (November 16th, 2020)
July 19th, 2019, 1:43 PM
#19
My travel trailer was 39 ft, weighed 11,000 lbs and I towed it with my extended 2006 Express 3500 6.0 and 3.73 gears. Yes it would seriously struggle uphill, I was stuck in 1 gear at 25mph. A 4500 lbs trailer is a small load for the 6.0, it should be merrily climb hills.