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95 sierra backfires now wont start

 
cobraracer89
I love my Chevy Chevette!
Posts: 2
Joined: 04/13
Posted: 04/11/13 12:26 AM

okay guys i have been working on my truck for the last couple days, im ready to give up and put a brick c4 in it to see how high i can blow it up. it has the 350 tbi.... so it started that i had a little hesitation of the line so i did my basic tune up on it cap rotor oil change and that took care of the problem for a little bit. it came back with a vengeance, it started to sputter a little but it gradually got worse it turned into a back fire issue and my truck would almost die then come back to almost full power a few days after this happened the truck cut out and stalled completely not like a great chugging stall it was nice and easy rolling stall i was able to get it started back up and ran fine for a little longer then did it again it finally got to the point where if i tried to put my foot into it it cut out and didnt want to go anywhere but if i slghtly tapped the gas it would accelerate so i babied it back to my house this way and shut the truck off it was late so i didnt look at it right then when i woke up and tried to start it it would start so i started to tear into it to diagnose the problem i checked the coil the ignition module and the pick up coil to see if any of them were faulty they all checked out just fine so thats when i decided it was timing went in to see if my distributor was just out of adjustment a little for some reason after tinkering with the distributor i was able to get it fired up went to make a test run to see if i solved the problem and a had a major loss of power so i turned it back around to the house i mean the good news on this was when i got into the throttle on it it didnt spit and cut out and backfire on me got it into my driveway shut it off and there it has sat since cause i cant get it to start up again so i decided time to go a little further with the timing and replaced the set so i have a new camshaft gear crank gear and chain in it got everything set baack to place and it wont fire up i double checked the pick up coil and it was just fine after that i took the ignition module to get tested again and it failed so i replaced that also i just checked the coil again just to be one hundred percent positive and its still checking out but it still wont fire it acts like it wants to but it wont fire up i know fuel pump and filter are a big thing that can cause a problem like this but i can tell you now that i am getting plenty of fuel to the throttle body and the injectors are working correctly i also checked my cap and rotor again rotor was cracked so i replaced it again i also checked my spark plugs and they are nothing out of the ordinary and also gapped just a tad wide but not enough i think to cause this kind of problem please any advice would be great cause me and my father are at a loss im at my wits ends on this truck and ready to go back to ford cause this problem has been having me stumped  

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redneckjoe69
I mow my lawn and find Chevys
Posts: 2337
Joined: 03/10
Posted: 04/11/13 05:02 AM

i had a similar problem once.  couldnt figure it out for anything.   did a full tune-up,...same problem.     turned out that i got moisture in the gas tank from not keeping much gas in it.  as soon as i got fresh gas, it ran perfect again.   its worth a shot.  you might get lucky?    i was just as frustrated as you mentioned.  i even changed the computer!  lol!   let us know what you find out.  

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68scott385
I mow my lawn and find Chevys
Posts: 1994
Joined: 10/09
Posted: 04/11/13 05:41 AM

Did you check the fuel pressure at the fuel rail, not just a visual check?  
68scott385 68scott385 68scott385

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waynep712222
I have an SS396 tatoo
Posts: 251
Joined: 03/13
Posted: 04/11/13 08:50 AM

first.. i am going to send you a private message.. with my phone number ..

second...

lets go over some of the ISSUES. that have effected OTHER TBI trucks...

got spark????   pull the coil wire from the distributer cap....   position it but don't hold on to it.. so the end is about 3/4" from a metal grounded item..     it should throw a 3/4" bright blue snappy spark..   if it won't throw more than a 1/4" of wimpy orange spark.. you have an ignition coil issue.. or the harness connectors or harness to it are bad...   there are under 10 buck adjustable coil spark output tester tool..  adjustable gap device with a gator clip to hook to ground..

COIL Highvoltageleakage

look at the sides of the coil for signs of high voltage leakage..



~~~~~~~~~~~~~~~~~~~~~~~~~~~~

next...  do you have a remote starter button..?? or figure out which is the starter relay in the power distribution box under the hood.. pull the relay.. use 2 small screw drivers to pull the guts out of the cover.. reinstall the bare relay frame.. when you push the contacts closed. the engine should crank... ...

pull the distributer cap...  note which position the #1 spark plug wire goes to...

using the relay, a remote starter button .. or a 15/16 socket on the alternator pulley nut.. to bring the rotor around to get close to where the #1 spark plug wire is in the cap...
now.. align the teeth of the reluctor and pick up coil without going past by turning the crank. this is where the 15/16 comes in handy...  

once you get the rotor lined up and the pickup coil and reluctor lined up..  look down at the crank damper timing marks..  the crank damper marks should line up with the pointer mark to match the base timing on the sticker....

... it is does..  you might want to pull the #1 spark plug..  stick either a compression tester hose into the hole.. or your finger over the hole... use the relay or the remote starter to crank the engine while you watch the rotor tip.. does it aim toward the #1 position when you are feeling the compression in the cylinder..   the crank rotates twice to one turn of the distributer..

distributers have been installed wrong in chevy's for decades...

when the cam sprocket is down.. the cam is set to fire the #6 cylinder.. when the CAM sprocket timing dot is at 12 o clock. its set to fire the #1 cylinder..

Sbccamtiming

now that we know the distributer is aiming the proper direction..  and on the proper stroke..

grab the ignition rotor.. wiggle the shaft side to side.. there should be NO clearance...

twist the rotor.. there should be NO rotational play in the distributer shaft..

pull the rotor...   take a good look down at the second layer of the reluctor.. is it showing cracks.. ...  cracks are bad,,  they will create GHOST patterns in the nice clean sine wave causing the ignition system to freak out..

Smallcapheicracks


this is a reman distributer that works better than the GM design..

V8smallcapheicardonereman


i have found the wiring connectors to the coil.. and from the ignition module to the coil bad...

you might want to pull the pair of connectors out of the coil..  or probe the thick red wire with a test light.. have somebody work the ignition key from the OFF position to ON.. cranking and back to ON. then off.. once it reaches ON.. till you turn it off. . you should NOT have any interuption in the power.. if you do.. you could have a bad ignition switch.. something that does happen...

~~~~~~~~~~~~~~~~~~~~

now that you have verified that the  ignition system is sparking...

lets look at the fuel system...

when somebody turns the key on... do you hear at the fuel tank.. the fuel pump run for 2 seconds????  you can listen .or you can probe the fuel pump fuse with a test light.. that fuel pump fuse is after the fuel pump relay and oil pressure switch contacts...

you should have power there for 2 seconds when you turn the key on.. and power while cranking.. .  this proves the power it getting to the fuel pump circuit..
as both the fuel pump relays in the relay box under the hood have been found to be bad.. the 3 wire oil pressure switch has been known to go bad..  the oil pressure switch and the fuel pump relay are wired in parallel... but both have to work or it will burn out the fuel pump relay...

i have also found the fuel pump relay really easy to install.. so i used a sharp tipped scribe to tighten the wiring terminals grip on the relay..

if you have good power at the fuel pump fuse..  but the pump does not run...  check the ground connection at the top of the frame rail inside the left rear tire...

Chevypickupfuelpumpgroundframe

in addition.. get under the front of the truck.. passenger side front.. battery disconnected..

on the bottom front of the block is a stack of ground wires .. take the nut off.. count the wires as they come off.. wire brush each one..  wire brush the stud..  wire brush the back of the nut.. reassemble..  i have found a LOT of GM trucks with this ground connection dirty...

way too many actually..

more to come...  

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waynep712222
I have an SS396 tatoo
Posts: 251
Joined: 03/13
Posted: 04/11/13 09:57 AM

another thing..

do you own a timing light... hook it up to one of the spark plug wires...

but don't worry about setting the timing..

i want you to aim the flashing light at the cone of spray from the injectors while the engine is cranking..  is it a NICE CRISP cone..  or a weak off center cone that would show lack of fuel flow and pressure??  

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waynep712222
I have an SS396 tatoo
Posts: 251
Joined: 03/13
Posted: 04/11/13 11:48 AM

after the call...

this is the ignition switch for the 95 model year..



Gmmusicboxignitionswitchcontacts

Gmmusicboxignitionswitchspool

Chevyignitionswitchcontactsopenclosed


Chevyignitionswitchtornapart


you will need on a 95 chevy ... your external torx socket set..


E4 thru E8    its mostly going to be E4 and E5... perhaps an E6 i was not paying a lot of attention to the sizes i used..



please also print this voltage drop test and run it...

i have found lots of issues on these trucks... where the ground connections at the engine block.. passenger side front..  are corroded...

VOLTAGE Drop Testing



lastly... set the harmonic damper to the base timing mark shown on your emission label on the core support...

rotate the distributer housing to  align the teeth of the pickup coil and the reluctor.. till they line up perfectly... then lock the distributer down.. this will get you base timing..  and allow you to start the engine and get it running so you can check it with a light when you find the disconnect to turn off the electronic spark timing ..  

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waynep712222
I have an SS396 tatoo
Posts: 251
Joined: 03/13
Posted: 04/11/13 12:08 PM

during on talk.. you described several issues.. and at over 230,000 miles..  the ignition switch is suspect... big time..

but it also sounds like the timing is not set properly..  




0996B43f80219b6e


Remove the column shroud halves.
Remove the column-to-dash attaching bolts and slowly lower the steering column, making sure that it is supported.
Remove the multi function switch if necessary.
Remove the key alarm switch, if equipped by gently prying the alarm switch retaining clip with a small screwdriver. Rotate the alarm switch 1 / 4 in. turn and remove.


WARNING
Extreme care is necessary to prevent damage to the collapsible column.

Make sure that the switch is in the Lock position. If the lock cylinder is out, pull the switch rod up to the stop, then go down one detent.
Disconnect the actuating rod from the switch.
Remove the two screws and the switch.

To install:
Before installation, make sure the switch is in the Lock position.
Attach the actuating rod to the switch.
Install the switch using the original screws. Tighten the screws to 12 inch. lbs. (1.4 Nm).
Install the key alarm switch, if equipped . Make sure the retaining clip is parallel to the lock cylinder. Rotate the alarm switch 1 / 4 in. turn until locked in place.
Install the multi function switch if removed.
Replace the column. Tighten the nuts to 22 ft. lbs. (29 Nm); the bolts to 20 ft. lbs. (27 Nm).
Install the column shroud halves.


this is the turn signal combo switch.. you will probably need to remove this also..

0996B43f80219b6d

this is a 93 emission label.. looks like timing on the 93 is 0  TDC...

0996B43f8020d651  

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