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94 chev van, no power, lousy gas milage

Tiny
JPB04619
  • MEMBER
  • 1994 CHEVROLET VAN
  • 42,000 MILES
1994 chev van, 41000 miles.G20, 5.7 liter.4l60e, 3:73 rear ratio. Low mileage vehicle, in tip top condition. But it will not get out of its own way, no power to accelerate and gas mileage is lousy. Fuel pressure 12 lbs plus. Checked timing with wire disconnected, 0 degrees, new cap and rotor, new ignition module, new tps, compression test 150 pounds or within 5 on all cylinders, new knock sensor. Kent moore tester on all spark plug wires checks out a1. All replaced parts acdelco with correct numbers. No cel light, no codes stored. Runs smooth as silk, starts easily
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Wednesday, September 5th, 2012 AT 7:21 PM

41 Replies

Tiny
KHLOW2008
  • MECHANIC
  • 41,815 POSTS
Have you checked for exhaust restriction?
Try cleaning the MAF
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Wednesday, September 5th, 2012 AT 7:48 PM
Tiny
JPB04619
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  • 22 POSTS
No cat converter, it was removed and has test pipe installed permanently. No maf but it does have a map sensor. Map sensor output checks out, shows 5 volt peak
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Wednesday, September 5th, 2012 AT 8:03 PM
Tiny
KHLOW2008
  • MECHANIC
  • 41,815 POSTS
Mechanical and electrical side seems good.

Though fuel pressure is correct, there could be restricctions causing insufficient flow during acceleration. Have you tested the operating pressure during acceleration?
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Wednesday, September 5th, 2012 AT 8:42 PM
Tiny
JPB04619
  • MEMBER
  • 22 POSTS
One thing I should have mentioned right at the start was this thing pings when you try to make it climb a hill;in the old hei distributor days I would have simply bumped the timing back a little till it stopped but I have no clue on this computer controlled truck. Like I said, I should have mentioned it right away .
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Thursday, September 6th, 2012 AT 12:55 PM
Tiny
KHLOW2008
  • MECHANIC
  • 41,815 POSTS
You can't do anything with the ignition timing as it is computer controlled and you have replaced the knock sensor so this pinging is strange.

Here are the diagnostic aids from the shop manual, see if it is of any help.

LACK OF POWER OR SLUGGISH

Symptom Definition

Engine delivers less power than expected. Little or no increase in speed when accelerator is applied.

Possible Causes & Corrections:

Check exhaust system for restrictions, such as a damaged or collapsed pipe, muffler or catalytic converter.

Check engine valve timing and compression.

Check engine for a worn camshaft.

Check TCC system for proper operation.

Check transmission shift pattern and downshift operation.

Using Spark Tester (ST-125), check for adequate spark output.

Ensure initial ignition timing is properly set.

Check ESC system for excessive retard.

Check EST system for proper operation.

Check air filter and fuel filter. Replace if necessary.

Ensure fuel system pressure is correct at all engine speeds.

Check for poor fuel quality or water-contaminated fuel.

Check injector wires for short to ground at air cleaner.

Check for spray from one injector on TBI unit. Malfunction may be present in injector assembly or in signal to injector assembly. Isolate malfunction by switching injector connectors. If problem remains with original injector, injector is defective. If malfunction moves with injector connector, problem is an improper signal in injector circuits.

Check PCM grounds. Ensure they are clean, tight and properly located.

Ensure EGR valve is not always open.

Check charging system output. Repair if output is less than 9 volts or more than 16 volts.

Check A/C for proper operation.
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Thursday, September 6th, 2012 AT 1:08 PM
Tiny
JPB04619
  • MEMBER
  • 22 POSTS
Other than the knock sensor and map, what does the computer look at to set the timing.
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Thursday, September 6th, 2012 AT 3:10 PM
Tiny
KHLOW2008
  • MECHANIC
  • 41,815 POSTS
TPS, VSS and transmission signals.
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Friday, September 7th, 2012 AT 4:28 AM
Tiny
JPB04619
  • MEMBER
  • 22 POSTS
I replaced the throttle ps with a new acdelco one, no difference. The speedometer reads correctly and has no problems. Does this mean the vss is not a problem and what or how do I check the transmission signals john b
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Friday, September 7th, 2012 AT 2:16 PM
Tiny
KHLOW2008
  • MECHANIC
  • 41,815 POSTS
If the transmission is shifting correctly and you have no trouble codes, that would rule that out as well.

Maybe you need to look at the gas you are using. Some treatment might make a difference.
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Friday, September 7th, 2012 AT 4:06 PM
Tiny
JPB04619
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I use the same gas in my pickup, same engine [tbi 350], same transmission[700r4], same rear ratio and the pickup is a 4x4, which means its heavier. The pickup works like a charm and the difference in power is sustantial and there is no spark ping from the pickup.
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Friday, September 7th, 2012 AT 4:12 PM
Tiny
KHLOW2008
  • MECHANIC
  • 41,815 POSTS
You might have to look at the mechanical aspect of the engine. Maybe the timing chains are stretched.

Is this problem new?
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Friday, September 7th, 2012 AT 4:24 PM
Tiny
JPB04619
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  • 22 POSTS
Easy service, mostly highway miles, 41,000 miles, cant see it. Compression test, all cyls within 5 lbs of 150 pounds. No problem is not new but seems to be getting worse, gas milage is slipping over the last few months john b
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Friday, September 7th, 2012 AT 4:56 PM
Tiny
KHLOW2008
  • MECHANIC
  • 41,815 POSTS
At 41 k miles, the engine is almost new. With everything looking in order, it seems strange.

Maybe you should be looking at the fuel flow. Possibly a partially clogged filter?
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Friday, September 7th, 2012 AT 5:04 PM
Tiny
JPB04619
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First thing I did was a new filter. Flow test, as I remember, was a pint in about 12 secs john b
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Friday, September 7th, 2012 AT 5:11 PM
Tiny
JPB04619
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Also, when climbing a hill it downshifts as it losses speed. In the lower gears the engine revs up and it will start to regain speed. If the fuel flow was restricted, would it be able to rev the engine up.
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Friday, September 7th, 2012 AT 5:15 PM
Tiny
KHLOW2008
  • MECHANIC
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It would depend on how bad the restriction is.
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Friday, September 7th, 2012 AT 5:27 PM
Tiny
JPB04619
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Is there a spec for fuel flow. John b
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Friday, September 7th, 2012 AT 5:30 PM
Tiny
KHLOW2008
  • MECHANIC
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I am running out of ideas. Are the spark plugs running clean?
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Friday, September 7th, 2012 AT 5:30 PM
Tiny
JPB04619
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  • 22 POSTS
Slight fouling in #3 cyl, now and 10,000 miles ago when I installed new acdelco plugs. No real buildup, compression 150 lbs + or - 5 on all cylinders. Engine as smooth as silk
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Friday, September 7th, 2012 AT 5:37 PM
Tiny
KHLOW2008
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  • 41,815 POSTS
I could not find any reference to fule flow amount, only pressure specs of which yours is correct.
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Friday, September 7th, 2012 AT 5:39 PM

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