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1994 454 LOSES POWER WHEN WARM

 
ctscoop
I love my Chevy Chevette!
Posts: 6
Joined: 01/12
Posted: 01/11/12 12:00 PM

I have a 1994 chevy 454 p series chassis, and it runs great when it is cold, but when you drive it 15 miles or so it will not go up a hill or slight grade, it just boggs out. This confususes me . I check the fuel pressure and it is 30, but when you give it gas the pressure drops to 18. any help on this issue would be great. Thanks  

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pepsi1
I mow my lawn and find Chevys
Posts: 1718
Joined: 09/11
Posted: 01/11/12 01:15 PM

ctscoop welcome aboard;

I would start by changing the fuel filter. If that doesn't do it I would say your going to be putting a fuel pump in it. Is that like small school bus? Grin  Cool

Thanks
Bob  

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pepsi1
I mow my lawn and find Chevys
Posts: 1718
Joined: 09/11
Posted: 01/11/12 01:24 PM

Sometime if there is dirt or foriegn material in the filter it will fall out of the paper element, and then as the engine starts using fuel again it will pick up the dirt and start plugging up the filter.

If you have to change the fuel pump, you may have to change the sending unit also. some companies are selling those parts as a unit. But change the fuel filter first. If it is the fuel filter with it plugging up its making the pump work harder.
Thanks
Bob  

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skyeking
I mow my lawn and find Chevys
Posts: 2738
Joined: 08/09
Posted: 01/11/12 03:42 PM

Hi there,
  Need I say that the largest best quality
  filters of any kind are the best long term
  investment.All the best with a well proven
  motor....Skyeking.....Hi Bob!!  
skyeking

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ctscoop
I love my Chevy Chevette!
Posts: 6
Joined: 01/12
Posted: 05/13/12 06:48 AM

Hey Guys thanks for your help earlier. The problem seem to be solved with changing the fuel pressure regulator, that was short lived. It will be runnign fine then all of the sudden loses power. if you unplug the injector cap and plug it back in it will run better for a short time then you never know how long it will be until it starts acting up again. I am going absolutely crazy with this problem.. Any help would be awesome..  The fuel pump and sender has been replaced. The filter has been replaced and the fuel pressure reg has been replaced. This is a 20 passenger bus..  

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waynep71222
I have an SS396 tatoo
Posts: 448
Joined: 03/12
Posted: 05/13/12 08:31 AM

i am taking that this is a Throttle body injected motor..   not a vortech fuel injected motor.  as that much fuel pressure is too much for a throttle body injected motor.. and not enough for a vortech motor..

can you with your engine idling.. open the relay box under the hood and pull the fuel pump relay out..  the engine should continue to run.. as it should be running the fuel pump circuit  on the contacts in the oil pressure switch. if the engine dies when you unplug the fuel pump relay..  change the oil pressure switch..   tighten the terminals in the fuel pump relay socket with a fine tipped tool..  by getting in sideways to the end of the terminal and lifting the folded tab slightly

first thing..  do you have a digital volt meter???   and do you have access to a scan tool that will work on this system..   94 and 95 are transition years.. scan tools are required..

this is the data for a slightly earlier TBI but the values should be the same...
TPS voltage should be on a TBI motor be about 0.65 volts at idle.
TBISCANDATE87

you are probably going to want to check the ground connections at the fuel tank frame rail..

Chevypickupfuelpumpgroundframe

94GMC C1500fuelpumpground


next...  if you can get at the distributer cap and rotor... use a bright flashlight and look at the center of the shaft below the rotor..

Smallcapheicracks

do you have cracks in the magnet that is the second level...  there are REMAN distributers with a totally different design reluctor.. a far far better design..    with electronic spark timing.. the cracks can cause ghost patterns in the waveform from the pickup coil to the ignition module, this really screws with the electronic spark timing..  causing the ignition to trigger random sparks..   the new design creates a really clean and strong waveform..


do you have a timing light???  hook it to any of your spark plug wires...  or the coil wire..  aim the flashing light at the spray cone from the injectors...   are the cones nicely shaped?  not random or intermittent..  fuel injectors can have internal windings that short out intermittently..  causing all kind of problems..  this is hard to spot sometimes with a digital OHM meter..  as the resistance is very low .. like 1.2 ohms.. and the thermal issues.. prevent the heating of the injector..   i do know of a test that will work.. but i really don't want to post it.. as i have on an other forum.. had somebody burn out all their injectors..  when they did not read the test instructions properly..  5 seconds means 5 seconds.. not 5 minutes..  or even 10 seconds..  bob knows what i am talking about.. he knows what test i am talking about.  and.. no he is not the person who burned them out.  

it really sounds like you might have internally shorted injectors.. or a bad ground..


next...  somewhere on the intake or cylinder heads is the 2 or 3 ground wires that come out of the fuel injector harness...   they are usually connected to the post behind the thermostat housing..  and also to the back of the cylinder heads...   they ALL have to be connected properly..

the last test for now.. and this is probably the first test you should do before anything else..

digital volt meter..  they are cheep.. 7 bucks to 25 bucks..

set to 20 volts DC... start engine and turn on headlights..

1.  test Negative battery post to positive battery post..   14.1 to 14.8 volts DC is expected.

2. test Negative battery post to the engine block..  0.04 volts is expected.

3. test Negative battery post to the body... 0.02 volts is expected..

4. test engine block to the body.. 0.02 volts is expected..

5   positive battery post to one of the fuses in the underhood relay and fuse box.. 0.02 volts..

this 5 part test takes about 2 minutes to do..  you might also want to test between the battery negative and the frame.. as the fuel pumps are grounded to the frame..  and the engine and body sit on isolators... so a loose ground wire would drive you crazy.. as the ground side provides all the electrons to power the devices..  bad ground.. no electrons to do the work..

post what you find..   i had a friend with a 98 C2500.. that on test 4 measured 8.5 volts..   fixed the ground cable connections at the bottom front of the block and cured most of the issues..
this was 8.5 volts between the BLOCK and the Body...  way wrong..





and you will want to print these instructions.. so you can follow them step by step...

feel free to ask questions.   pepsi1 and i are both professional auto mechanics with decades of experience..  

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ctscoop
I love my Chevy Chevette!
Posts: 6
Joined: 01/12
Posted: 05/15/12 12:59 AM

Thanks for the info, I will check this out and let you know how it works.  

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ctscoop
I love my Chevy Chevette!
Posts: 6
Joined: 01/12
Posted: 05/15/12 01:10 AM

THIS THING HAS BEEN DRIVING ME ABSOLUTELY CRAZY! i REALY APRECIATE ALL OF YOUR HELP AND WILL LET YOU KNOW THE OUTCOME.  

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ctscoop
I love my Chevy Chevette!
Posts: 6
Joined: 01/12
Posted: 05/15/12 05:18 AM

.  test Negative battery post to positive battery post..   14.1 to 14.8 volts DC is expected.  Tested and got 14.68

2. test Negative battery post to the engine block..  0.04 volts is expected.
Tested and got 0.48
3. test Negative battery post to the body... 0.02 volts is expected..
Tested and got 0.62
4. test engine block to the body.. 0.02 volts is expected..
Tested and got 0.48
5   positive battery post to one of the fuses in the underhood relay and fuse box.. 0.02 volts..
Tested and got 0.01

I hope this information is helpful. Is this pointing to a grounding issue?  

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pepsi1
I mow my lawn and find Chevys
Posts: 1718
Joined: 09/11
Posted: 05/15/12 05:50 AM

I ahould have asked this earlier: Is this a new rebuilt engine!

Bob  

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ctscoop
I love my Chevy Chevette!
Posts: 6
Joined: 01/12
Posted: 05/15/12 07:00 AM

No,it is not.  i just ran the 20vdc test again and it showed that neg post to block/intake was showing 0.01  
Neg post to body0.10
engine block to body 0.00  

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waynep71222
I have an SS396 tatoo
Posts: 448
Joined: 03/12
Posted: 05/15/12 08:22 AM

did you have the headlights on for the second test.. ?   circuits have to be active for the voltage drop test to work..

do you have a second car or truck to practice this test..

you still have a ground issue...   under the truck.. front of the motor passengers side is usually where the ground cable from the battery attaches...    you will usually find several ground connections on that stud..  count the wires.. take them off.. wire brush the ring terminals.. and the studs and back of the nuts..  if the engine was rebuilt..    take the stud out and clean the paint off the area where the stud attaches..

you may find the battery negative cable there..  

you may find the engine to frame cable there

you may find the engine to body cable there..

you may want to clean the other ends..

sounds like the battery positive to the relay box is good...

there is usually a ground strap to the back of the cylinder heads to the firewall..  you might want to climb in and verify that.. i don't recall but it might take a 15MM wrench for the bolt..   that area of the back of the head may need to be cleaned of paint also..  

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