97 tahoe backfires when cranking, no start


steve porter
04-23-2011, 11:00 AM
bought a 97 tahoe for a killer price. the guy was no mechanic. said that it was running fine. the next day whent to start and nothing. all he did is replace plugs and wires and fuelfilter. i towed it home and procedied to fix it. i have rebulit one of these engines before in my 99 suburban, so i am familair with working on it. when you try to start it it will turn over fine for a min and then act like it is out of time and backfire from the intake, and also load up and not turn over. i have replaced the cam and crank postion sensor, and nothing i unpluged the ingtion module and it turnover just fine no problem just would not start. i replaced that and it did the same as before . so im lost now i have cleared codes, it has blue spark , fuel, not sure on pressure yet im checking now. i try to spray starting fluild in to intake and it just backfires and starts a flame. need some info please ty. i need the tahoe for school ty again

mcmalloy
04-23-2011, 11:51 AM
Is it a vortec engine,

j cAT
04-23-2011, 12:26 PM
bought a 97 tahoe for a killer price. the guy was no mechanic. said that it was running fine. the next day whent to start and nothing. all he did is replace plugs and wires and fuelfilter. i towed it home and procedied to fix it. i have rebulit one of these engines before in my 99 suburban, so i am familair with working on it. when you try to start it it will turn over fine for a min and then act like it is out of time and backfire from the intake, and also load up and not turn over. i have replaced the cam and crank postion sensor, and nothing i unpluged the ingtion module and it turnover just fine no problem just would not start. i replaced that and it did the same as before . so im lost now i have cleared codes, it has blue spark , fuel, not sure on pressure yet im checking now. i try to spray starting fluild in to intake and it just backfires and starts a flame. need some info please ty. i need the tahoe for school ty again

USING STARTER FLUID UNLESS YOUR A PRO CAN BE DANGEROUS ! only a 1 second spray no more.....

since the plugs/wires were replaced then it would not start remove the wires/plugs inspect for defects including resistance of the wires..then using a diagram reinstall the plug wires correctly..this is a 5.7L engine correct ? remove distributor cap at this time and check for defects and the distributor for defects like the cam gear or the distributor bearings.

cold start you need 62-65 psi of fuel pressure use a guage.

if 58 psi it may not start ..............

steve porter
04-23-2011, 12:57 PM
it is a vortec model. i tested the fuel pressure and at key on it went to 65psi and bled off to 0 fast. at cranking it is fine but when you stop it bleed to 0 fast. i pulled # 1 plug and it is fuel fouled. as i had the #1 plug wire off and was cranking it was cranking fine with no backfire from intake. put on plugwire and it started to backfire from intake again going to put a new cap and rotor on and new plugs also. any suggestion on the fuel leak down ty

777stickman
04-23-2011, 05:44 PM
Fuel press bleed off could be the press reg or the check valve in the tank sending unit.

Back firing could be improper plug wire routing, cracked dist cap, bad rotor, ign timing off, valve timing off, valve adjustment off, etc, etc.

Too bad you cleared the codes. Would be nice for us to know what they were. For future reference, clearing the codes does nothing to make the motor run better.

Stingray11
04-23-2011, 06:46 PM
I would start with a new cap and rotor. I have seen a lot of those on both the V8 and V6 Vortec engines cause no starts with your description.

David

j cAT
04-23-2011, 06:59 PM
it is a vortec model. i tested the fuel pressure and at key on it went to 65psi and bled off to 0 fast. at cranking it is fine but when you stop it bleed to 0 fast. i pulled # 1 plug and it is fuel fouled. as i had the #1 plug wire off and was cranking it was cranking fine with no backfire from intake. put on plugwire and it started to backfire from intake again going to put a new cap and rotor on and new plugs also. any suggestion on the fuel leak down ty

if the engine is getting flooded the loss of fuel pressure with shut down of fuel pump to zero fast maybe injectors/regulator leak...check these out first. then going to the fuel filter hook up pressure guage. with no injectors or regulator with key on then off fuel pressure should hold ..if it rapidly falls then you know fuel pump check valve is defective..NEED NEW PUMP..

MAKE SURE THE PLUG WIRES ARE CORRECTLY INSTALLED..ETC..

steve porter
04-23-2011, 07:44 PM
well when i ran the scan there was no codes so i took back the $300 CODE READER and got my money back. went and bought a new fuel pressure reg. and gaskets to take the inlet plentum off after taking that off i found that the spider was burnt on a couple of the arms so i replaced it and a new reg. also bought new plugs , cap, and rotor. getting ready to finish it up now will post what happen. im also going to reset the timing in it again or see if it is off or not. ty

steve porter
04-23-2011, 10:21 PM
got it running now thanks for all of your help out there now i need to relearn the crankshaft postion sensor and reset timing. runs great thank again

j cAT
04-24-2011, 08:56 AM
got it running now thanks for all of your help out there now i need to relearn the crankshaft postion sensor and reset timing. runs great thank again

good troubleshooting ! you should be fine with what components you replaced for a long time.

I would change the oil very soon...get all that damaged oil out of the crankcase..even do a 2x oil change just to be sure you get all the sludge out of the engine, fuel will break down the sludge as well as damage the oil with poor lubrication.

Stingray11
04-24-2011, 09:41 PM
good troubleshooting ! you should be fine with what components you replaced for a long time.

I would change the oil very soon...get all that damaged oil out of the crankcase..even do a 2x oil change just to be sure you get all the sludge out of the engine, fuel will break down the sludge as well as damage the oil with poor lubrication.
+1 on the oil change!

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