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tbi running to rich

 
USMCddog1
I love my Chevy Chevette!
Posts: 1
Joined: 08/10
Posted: 08/16/10 08:14 AM

i just bought an 87 chevy pickup that is running to rich. it is starting to back fire and will stall out when at an idle. just wondering how to adjust the tbi  

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idrivejunk
My first time was in a Chevy
Posts: 128
Joined: 04/10
Posted: 08/16/10 01:15 PM

It might just be a bad temp sensor telling the tbi that the engine is cold.  
idrivejunk

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waynep7122
Everything in my driveway’s a Chevy
Posts: 556
Joined: 08/09
Posted: 08/16/10 07:55 PM

i totally agree...

first to check...  is the distributer cap...    make sure the coil has not started leaking high voltage from the center windings...    

make sure the pick up coil is not rusted..   breaking up...

make sure the ignition rotor has not burned through..

when was the last time you changed the fuel filter????  is your fuel pump noisy???


(why worry about the fuel pump.. and the fuel filter...  when they clog or fail...  the Ecm trys to keep the correct amount of fuel going into the motor via  looking at the oxygen sensor signal..  it starts opening the injectors for a longer time.. causing weird rich problems)



if you can borrow a scan tool...      plug it in.. write your data on the proper line of this chart.. then post whats out of whack..     open this image in a new window.. and print it...

Scandata

also.. is the check engine light on?????

it will have codes that are easily accessed... to point you toward the part of the system with problems..

don't just replace  parts pointed out  by a code...  diagnose  by the code numbers...

you might also want to clean the ground wires on the stud behind the thermostat housing.. they have to be clean.. tight.. properly terminated..

TBI system are easy to fix... easier than carbs...   once you understand...  like a few of us do totally.. which is why we help...  

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55Guy
Administrator
Posts: 1153
Joined: 07/06
Posted: 08/17/10 01:56 PM

I've got a '92 Silverado with the TBI system. There are 3-4 main things that could be causing this trouble. First is the TPS sensor has gone bad (would trip the check engine light). Second would be a bad oxygen sensor (sometimes will or won't trip the check engine light), third is the magnetic pickup in the distributor going bad (as far as I know won't trip the check engine light) and fourth is the temp sensor.  

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ahkmed
I love my Chevy Chevette!
Posts: 1
Joined: 07/13
Posted: 07/29/13 10:42 AM

i have and 89 gmc pick up with a 5.7 tbi. it idles rough has a strong gas smell  and will die at when put in reverse and when you come to a stop. ive replaced all the plugs they were black. dist cap and rotor button they were burnt. fuel filter gas was a very dark brown color. iac, map, cts, and tps, checked for vaccuum leaks the egr is working properly. and when you hit the gas it wants to bog down. light acceleration is fine but anything else it bogs down. could this be my timing?  

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waynep712222
V-6 Camaros rule!
Posts: 122
Joined: 03/13
Posted: 07/30/13 02:13 AM

Icon Quoteahkmed:
i have and 89 gmc pick up with a 5.7 tbi. it idles rough has a strong gas smell  and will die at when put in reverse and when you come to a stop. ive replaced all the plugs they were black. dist cap and rotor button they were burnt. fuel filter gas was a very dark brown color. iac, map, cts, and tps, checked for vaccuum leaks the egr is working properly. and when you hit the gas it wants to bog down. light acceleration is fine but anything else it bogs down. could this be my timing?

did you change the fuel filter????

take the filter back off..    run the line from the tank  that connects to the filter into a plastic bottle.. cycle the key on and off a few times..  you could have a bunch of dirty gas in the fuel line from the tank...

verify that the new fuel filter is NOT clogged again...

you could have an in tank fuel pump going bad.. since there are NO fuel pressure test ports on the TBI fuel pipes.. its hard to tell whats going on..

the fuel pump should make 25 PSI when deadheaded.. at the filter .. finding some kind of fitting to adapt to the gauge will be hard..

you can also.. aim a timing light at the spray cone from the throttle body fuel injectors.. it should be a nice cone shape.. without any missing areas..

low fuel pressure will create a random pattern that may be offset..

please also check the ignition coil exterior for signs of high voltage leaks..

if this is a small cap HEI.. pull the cap and rotor and check for carbon tracking.. or build up on the cap terminals.. signs of burn thru on the rotor..
while you have the cap off.. please look at the second layer of the reluctor..  its visible around the shaft as the second layer.. it you see cracks.. you will need to replace the distributer.. reman units have a different design from some manufacturers..  they work really well...

if you have a digital volt meter with a 15 or 20 AMP DC setting.. 10 amps will usually work but..

you can jump the fuse terminals with the amp meter and see the amp draw.. right around 7 amps DC is good.. more than 7.5 is bad...

how did you check the various sensors..   did you check for codes... do you have access to an OBD1 scan tool to look at the live data stream..  

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