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 Page 1 of 2 12
Username Post: This ones got me STUMPED        (Topic#355119)
marcgyver77 
Poster
Posts: 28

Age: 61
Loc: United States
Reg: 03-29-14
02-05-19 08:14 PM - Post#2759158    

Trying to figure this out... '97 Express, 5.0 (have had since new). Went from average 18 MPG to barely 13 MPG.
Engine runs strong, idles good, accelerates good. 20 psi vacuum at idle.

Replaced: Plugs, wires(routed un-touching), cap, rotor, upstream & down stream O2 sensors, muffler, air filter, fuel filter, PVC valve, vacuum hoses

Plugged off EGR to eliminate that as a problem(appeared that it was working correctly).

Cleaned Mass air (with correct cleaner).

Run Sea Foam thru gas tank and thru intake via vacuum line.

Timing advances. Used programmer to advance timing to various settings with little results.

No check engine codes (other than EGR after plugging)

Checked MPG both with speedometer and GPS.

Other than heavy carbon build up inside tailpipe from running rich (or checking MPG on my 160 mile weekly commute), you would think its running good...

Any ideas



 
454cid 
Valued Contributor
Posts: 3089

Age: 46
Loc: West Michigan
Reg: 02-18-12
02-05-19 08:28 PM - Post#2759161    
    In response to marcgyver77

  • marcgyver77 Said:
Trying to figure this out... '97 Express, 5.0 (have had since new). Went from average 18 MPG to barely 13 MPG.
Engine runs strong, idles good, accelerates good. 20 psi vacuum at idle.

Replaced: Plugs, wires(routed un-touching), cap, rotor, upstream & down stream O2 sensors, muffler, air filter, fuel filter, PVC valve, vacuum hoses

Plugged off EGR to eliminate that as a problem(appeared that it was working correctly).

Cleaned Mass air (with correct cleaner).

Run Sea Foam thru gas tank and thru intake via vacuum line.

Timing advances. Used programmer to advance timing to various settings with little results.

No check engine codes (other than EGR after plugging)

Checked MPG both with speedometer and GPS.

Other than heavy carbon build up inside tailpipe from running rich (or checking MPG on my 160 mile weekly commute), you would think its running good...

Any ideas



What temperature does the PCM think the engine is? If your coolant temperature sensor is bad (or the wiring) and the PCM thinks the engine is cold, it's going to run rich.


99 K3500 RCLB


 
rockfangd 
"6th Year" Gold Supporting Member
Posts: 2639
rockfangd
Age: 33
Loc: Utica ny
Reg: 04-13-10
02-05-19 09:05 PM - Post#2759166    
    In response to 454cid

agreed.
Look at the ECT readout on a scantool.
when the engine is cold the coolant temp should be within 4*+- of ambient temperature.


Old School GM fan FOREVER


 
marcgyver77 
Poster
Posts: 28

Age: 61
Loc: United States
Reg: 03-29-14
02-06-19 03:16 PM - Post#2759221    
    In response to 454cid

I hurried home to plug in my scanner even though the engine was at operating temp. The coolant temp showed 178 Deg , the intake temp was at 111 and rose to 121 while sitting there idling. I scrolled thru...intake vacuum good, mass air was at 6-7 at idle... most of the other (bank 1, bank 2, etc) was Greek to me. I could write them down if it would help diagnose the problem.

I was optimistic about it being an easy fix...Lol
I can wait till it cools off if it has to be checked cold...



 
454cid 
Valued Contributor
Posts: 3089

Age: 46
Loc: West Michigan
Reg: 02-18-12
02-06-19 03:49 PM - Post#2759225    
    In response to marcgyver77

  • marcgyver77 Said:
I hurried home to plug in my scanner even though the engine was at operating temp. The coolant temp showed 178 Deg



That's a little low, but not much. Do you only have a 180 degree thermostat instead of a 195?

  • Quote:
mass air was at 6-7 at idle.



That's a little high... the book says 5.80, for the 5.0/5.7, so if you're seeing 7 at idle, it could be the PCM is adding fuel to try to make the mixture right. I had the opposite problem... my MAF was reading low, at only 2. I got a salvage yard MAF.

I'm not very experienced in this kind of thing, so don't take this as definitive.

You could try unplugging the MAF, and see if anything changes. The PCM will switch to speed density mode.

99 K3500 RCLB


 
Shepherd 
Frequent Contributor
Posts: 1697

Loc: Lake George, NY
Reg: 11-11-15
02-06-19 04:23 PM - Post#2759229    
    In response to 454cid

A lazy o2 sensor can cause and not set a code until it caused the fuel map to go out of it's program limits.



 
marcgyver77 
Poster
Posts: 28

Age: 61
Loc: United States
Reg: 03-29-14
02-06-19 05:25 PM - Post#2759235    
    In response to 454cid

It is only a two mile drive from work.
So I went back to update/clarify readings:
At idle, in neutral, 666 RPM, MAF 5.7 to 5.9

At idle, in neutral, AC on, 695 RPM, MAF 7.1 (AC was on when I checked it earlier... hot day today in Georgia).

At 157 degrees, thermostat opened ie. 160 thermostat.

Didn't understand what you meant by unplugging MAF.

Thank you for your help...



 
marcgyver77 
Poster
Posts: 28

Age: 61
Loc: United States
Reg: 03-29-14
02-06-19 05:34 PM - Post#2759236    
    In response to Shepherd

I replaced both of the upstream (2 months ago) and the one downstream (last week) with Bosh sensors. But with everything made in China...??? who knows???. Although they did not make a difference.



 
Shepherd 
Frequent Contributor
Posts: 1697

Loc: Lake George, NY
Reg: 11-11-15
02-06-19 07:09 PM - Post#2759241    
    In response to marcgyver77

Why a 160 thermo, you need 195 for proper ecm controls for the fuel map and timing.



 
454cid 
Valued Contributor
Posts: 3089

Age: 46
Loc: West Michigan
Reg: 02-18-12
02-06-19 07:15 PM - Post#2759242    
    In response to marcgyver77

  • marcgyver77 Said:
It is only a two mile drive from work.
So I went back to update/clarify readings:
At idle, in neutral, 666 RPM, MAF 5.7 to 5.9



That sounds better.

  • Quote:

At 157 degrees, thermostat opened ie. 160 thermostat.



I'd get that out of there. Put a 195F in it, or at least one in the 180's but it was programed for 195F unless you've had the PCM changed.

  • Quote:
Didn't understand what you meant by unplugging MAF.



The truck will run without it. The computer switches to Speed Density, but never mind, because it sounds like your MAF is in spec.



99 K3500 RCLB


 
rockfangd 
"6th Year" Gold Supporting Member
Posts: 2639
rockfangd
Age: 33
Loc: Utica ny
Reg: 04-13-10
02-06-19 08:17 PM - Post#2759248    
    In response to 454cid

How long has that 160 stat been in there?

Old School GM fan FOREVER


 
marcgyver77 
Poster
Posts: 28

Age: 61
Loc: United States
Reg: 03-29-14
02-06-19 10:19 PM - Post#2759262    
    In response to rockfangd

I am not sure. I will have to look at my receipts. I replaced the water pump 09/2015 along with the hoses and fan clutch. I think I would have replaced the thermostat while I was right there...and got the right one called out for it...
I will get a new one tomorrow and change it out before my weekly commute home (I work out of town in Savanna four days and go home on the weekends).



 
CowboyTrukr 
"8th Year" Silver Supporting Member
Posts: 4190
CowboyTrukr
Loc: Salt Lake City
Reg: 06-20-09
02-07-19 11:16 PM - Post#2759357    
    In response to marcgyver77

Gonna go out on a limb here and suggest part of the problem is Bosch O2 sensors.

Greg

'95 K1500 Z71 EC Short Step 5.7L+0.040/NV3500
'00 Explorer XLT 4.0 V6 Auto
'94 K2500 5.7 NV4500 ECLB - SOLD
‘87 GMC S15 SCLB 4.3 Auto - SOLD

"The only thing necessary for evil to triumph is for good men to do nothing" Sir Edmund Burke


 
4dr 57 
Valued Contributor
Posts: 4574
4dr 57
Loc: Texas Hill Country
Reg: 11-10-04
02-08-19 10:21 AM - Post#2759388    
    In response to marcgyver77

Is your engine an OBD1 system? Do O2 sensors come in two flavors like OBD1 and 2?
Stan



 
Shepherd 
Frequent Contributor
Posts: 1697

Loc: Lake George, NY
Reg: 11-11-15
02-08-19 11:18 AM - Post#2759394    
    In response to 4dr 57

97 should be obd11, most sensors are heated so usually 4 wires. If 2 wire or one, not heated.



 
CowboyTrukr 
"8th Year" Silver Supporting Member
Posts: 4190
CowboyTrukr
Loc: Salt Lake City
Reg: 06-20-09
02-08-19 11:40 AM - Post#2759396    
    In response to Shepherd

‘97 is OBD2

Greg

'95 K1500 Z71 EC Short Step 5.7L+0.040/NV3500
'00 Explorer XLT 4.0 V6 Auto
'94 K2500 5.7 NV4500 ECLB - SOLD
‘87 GMC S15 SCLB 4.3 Auto - SOLD

"The only thing necessary for evil to triumph is for good men to do nothing" Sir Edmund Burke


 
marcgyver77 
Poster
Posts: 28

Age: 61
Loc: United States
Reg: 03-29-14
02-08-19 08:34 PM - Post#2759444    
    In response to marcgyver77

Well... I replaced both the thermostat (with a 195 degree) and the coolant temperature sensor.
Filled up, left Savanna to go to Concord, about 3 1/2 hour drive, temperature came up to between 194 to 197 degrees. Idle dropped to 620 RPM, MAF was 5.8, seemed to run good.
Drove 280 miles, put 20 gallons of gas in, 14 MPG...

STILL STUMPED





 
marcgyver77 
Poster
Posts: 28

Age: 61
Loc: United States
Reg: 03-29-14
02-08-19 08:52 PM - Post#2759445    
    In response to CowboyTrukr

  • CowboyTrukr Said:
Gonna go out on a limb here and suggest part of the problem is Bosch O2 sensors.



Is there an issue with the Bosch sensors? Replacing the original O2's out with the Bosch ones didn't (seem to) make a bit of difference (nether better or worse).

Yes, it is OBD2




 
bowtie44s 
Valued Contributor
Posts: 4165
bowtie44s
Age: 36
Loc: wv
Reg: 08-29-12
02-08-19 09:43 PM - Post#2759448    
    In response to marcgyver77

I don't know how you got 18 before, but 14 is pretty good. I've had a few 350 trucks and 14 was what they got. The Express van probably has 1000lbs on the pickups. The 305 is smaller, but it works harder. They don't get better mileage than a 350 and a lot of times they get worse. I'd be happy with 14.

Jeff

'88 Chevy K3500, aluminum head roller cam 511in³ stroker 10.5:1 compression, 96 NV 4500, 94-98 grille, 305/70-16 (33x12) BF Goodrich KM2s, 91 cluster swap


 
rockfangd 
"6th Year" Gold Supporting Member
Posts: 2639
rockfangd
Age: 33
Loc: Utica ny
Reg: 04-13-10
02-08-19 10:12 PM - Post#2759450    
    In response to bowtie44s

14 is good on my 5.7l.
I dont think I have ever gotten any better than that. OBD1 though

Old School GM fan FOREVER


 
454cid 
Valued Contributor
Posts: 3089

Age: 46
Loc: West Michigan
Reg: 02-18-12
02-08-19 10:56 PM - Post#2759452    
    In response to marcgyver77

Have you changed anything else, like tires (possibly size), or the way you're calculating your mileage? How fast are you driving? Have you always driven that speed? You're mileage will drop over 65mph.

99 K3500 RCLB


 
CowboyTrukr 
"8th Year" Silver Supporting Member
Posts: 4190
CowboyTrukr
Loc: Salt Lake City
Reg: 06-20-09
02-09-19 01:19 AM - Post#2759453    
    In response to 454cid

Marc, many here have experienced problems with the Bosch O2’s. OEM is best.

Greg

'95 K1500 Z71 EC Short Step 5.7L+0.040/NV3500
'00 Explorer XLT 4.0 V6 Auto
'94 K2500 5.7 NV4500 ECLB - SOLD
‘87 GMC S15 SCLB 4.3 Auto - SOLD

"The only thing necessary for evil to triumph is for good men to do nothing" Sir Edmund Burke


 
junky 
Valued Contributor
Posts: 2898

Loc: Northeast CT
Reg: 06-27-10
02-09-19 10:17 AM - Post#2759469    
    In response to CowboyTrukr

I bought a Bosch O2 sensor for my wife's PT Cruiser on eBay, and the scan showed that it was "defective", even though it was new in what I believed to be a Bosch packaging. Bought an OEM from the Chrysler dealer, which was also a Bosch, and problem solved at 3 times the cost. I believe that a lot of what is being sent into the country might be counterfeits, or those that don't pass quality control (if there is such a thing) in China.

Never argue with an idiot. He'll drag you down to his level, then beat you with experience.


 
rockfangd 
"6th Year" Gold Supporting Member
Posts: 2639
rockfangd
Age: 33
Loc: Utica ny
Reg: 04-13-10
02-09-19 10:27 AM - Post#2759470    
    In response to junky

I do not buy bosch anything. I like to stick with Denso for o2 sensors

Old School GM fan FOREVER


 
454cid 
Valued Contributor
Posts: 3089

Age: 46
Loc: West Michigan
Reg: 02-18-12
02-09-19 11:47 AM - Post#2759474    
    In response to CowboyTrukr

My rear O2 sensors are Bosch, and I don't believe I've had any problem with them, however, they don't change the way the truck runs. Only the fronts to that.

It's weird that Bosch plugs and O2 sensors have a bad reputation when they're the biggest OEM producer of parts in the world. Must be their after-market line isn't the quality that the OEM parts are.

I have a pair of Bosch O2s for the front that I've never installed, as I couln't get the originals out at the time. It's irritating to think I really should buy different new ones. I wonder if NTK would be any good.

99 K3500 RCLB


 
bowtie44s 
Valued Contributor
Posts: 4165
bowtie44s
Age: 36
Loc: wv
Reg: 08-29-12
02-09-19 12:07 PM - Post#2759477    
    In response to 454cid

  • 454cid Said:
It's weird that Bosch plugs and O2 sensors have a bad reputation when they're the biggest OEM producer of parts in the world. Must be their after-market line isn't the quality that the OEM parts are.



The only experience I have with Bosch is spark plugs. I told the wife to pick me up some AC Delcos. They were sold out but the parts store guy told her these Bosch were way better. Against my better judgement I put them in. I had a terrible miss. I took them out and put ACs in and it ran great.

Jeff

'88 Chevy K3500, aluminum head roller cam 511in³ stroker 10.5:1 compression, 96 NV 4500, 94-98 grille, 305/70-16 (33x12) BF Goodrich KM2s, 91 cluster swap


Edited by bowtie44s on 02-09-19 12:07 PM. Reason for edit: No reason given.

 
marcgyver77 
Poster
Posts: 28

Age: 61
Loc: United States
Reg: 03-29-14
02-09-19 05:38 PM - Post#2759502    
    In response to bowtie44s

Sorry Bowtie, not a response to you but a reply to earlier POSTS

Here is the advertised specs for the 1997 Express cargo van:
ENGINE SPECS – 5.0 4AT (223 HP)
CYLINDERS
V8
DISPLACEMENT
5012 cm3
POWER
164 KW @ 4600 RPM
223 HP @ 4600 RPM
220 BHP @ 4600 RPM
TORQUE
280 lb-ft @ 2800 RPM
380 Nm @ 2800 RPM
FUEL SYSTEM
Electronic Injection
FUEL
Gasoline
PERFORMANCE SPECS
TOP SPEED
-
ACCELERATION 0-62 MPH (0-100 KPH)
-
FUEL ECONOMY SPECS
CITY
14 mpg US OR 16.8 L/100Km
HIGHWAY
19.4 mpg US OR 12.1 L/100Km
COMBINED
14.1 mpg US OR 16.7 L/100Km



Here is a post from a “Gold member”: My 6,200 lbs 1997 Express G1500 Conversion van running the factory 4L60E and 3.42s in the 8.5" 10-bolt it would pull down 18-20 mpg highway at 70-75 mph but it was GUTLESS compared to the way it runs now…

I just put on my third set of Michelin LTX tires. The speedometer was reprogrammed to tire size and matches my GPS within 1 mile of 170 mile weekly commute home.

The way I have been checking my mileage has been like this:
• Fill up to the second shutoff click in Savanna when I leave
• Fill up to the second shutoff click in Byron, 170 miles away (interstate with cruise control)
• Miles divided by gallons = MPG (I’m 61, so that’s the old math way…Lol)

The best mileage was last week, when for the first time, I programmed it for premium fuel (max timing advance), running at 85 MPH, used 11.8 gallons.
Two weeks ago, running 75 MPH, regular fuel program, used 12.3 gallons
On the way back, running 70 MPH, used 12.8 gallons.

So I’m going to rule out O2 sensors just for the moment, seeing there was no difference when I replaced them with the questionable Bosch ones. Still could be an issue.

The new Engine Temperature Sensor brought the reading to the PCM up from 178 to 197. Lowered the RPM down to 620 from 660. MAF at a steady 5.8
Mileage went up a little bit.

What else could be wrong?
Why do I get better mileage at 75+ MPH than under 70 MPH.

Fuel injectors worn out? Spraying or leaking fuel into the intake? Wouldn’t the PCM read that and compensate for it, or emit a “Check Engine”?

STILL STUMPED




Edited by marcgyver77 on 02-09-19 05:43 PM. Reason for edit: No reason given.

 
454cid 
Valued Contributor
Posts: 3089

Age: 46
Loc: West Michigan
Reg: 02-18-12
02-09-19 05:48 PM - Post#2759503    
    In response to marcgyver77



  • Quote:
I just put on my third set of Michelin LTX tires. The speedometer was reprogrammed to tire size and matches my GPS within 1 mile of 170 mile weekly commute home.


  • Quote:

...I programmed it for premium fuel (max timing advance), running at 85 MPH, used 11.8 gallons.



So you changed tires size? How are you "programming" the PCM?



99 K3500 RCLB


 
marcgyver77 
Poster
Posts: 28

Age: 61
Loc: United States
Reg: 03-29-14
02-09-19 06:02 PM - Post#2759505    
    In response to 454cid

I am using factory tire size. Using a Jet programmer to enter the actual tire diameter size. Checked accuracy by the Hwy mile markers and my GPS.

The Jet programmer has three fuel programs to choose from (regular, mid grade, premium) if you don't want to do a custom program. I thought i would give it a shot to see what it would do. (Can't set the timing the old school way- turn it till it clatters and back it off...Lol)



Edited by marcgyver77 on 02-09-19 06:14 PM. Reason for edit: No reason given.

 
bobb 
Super Senior Member
Posts: 5404
bobb
Loc: paradise
Reg: 09-05-03
02-10-19 09:48 AM - Post#2759541    
    In response to marcgyver77

what is your fuel pressure? does it hold pressure after the engine is turned off? o2 sensor readings should fluctuate allot when blipping the throttle or adding propane to the intake

70 L camino, grampa engine, g-force 5 spd, road rage suspension. Pray first before all else fails.


 
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