97 yukon backfireing thru intake.

[nokuy97]

Hi,
I have a 97 with a 5.7 with 145,000 on the clock. I let a friend use it for the last couple of months, next it gets droped off in my yard by a flat bed. He tells me it's been running fine until he went out one morning and it just cranked and almost started and then he killed the battery.
I went out and checked the fuel pressure and when I turn the key on the gauge goes up to 60psi , so then I am thinking spark problem. I took off the dis. cap and rotor and they don't look bad and put them back. Then I checked for codes and there are none. SOOO what do you think , the coil maybe. If you let it sit a day and try to start it wants to but it just acts like it is flooded and keeps back fireing out the intake ?

Any ideas ?

 

[retorq]

Back firing thru the intake is a timing issue ... check base timing, verify TDC and that the distributor is actually turning when the engine is cranked ...

 

[bowtiefreak]

^^^timing

 

[black95]

+1 timing

 

[nokuy97]

So in other words it may have jumped time in some way. I will check that the dis. is turning and make sure the timing is correct.


Thanks

 

[SunlitComet]

Try this:


DEFINITION
The fuel ignites in the intake manifold, or in the exhaust system, making a loud popping noise.

PRELIMINARY CHECK
Refer to Important Preliminary Checks . See: Computers and Control Systems\Testing and Inspection

IGNITION SYSTEM CHECKS

* Check for the proper ignition coil output voltage with the spark tester J 26792 or the equivalent.
* Check the spark plugs.
* Remove the spark plugs.
* Check for the following items:
* Wet plugs
* Cracks
* Wear
* Improper gap
* Burned electrodes
* Heavy deposits
* Check the ignition system. Refer to Enhanced Ignition System . See: Computers and Control Systems\Testing and Inspection\Component Tests and General Diagnostics\Enhanced Ignition System Check
* Check for crossfire between spark plugs (distributor cap, spark plug wires, and proper routing of the plug wires). Refer to Engine Electrical.

ENGINE MECHANICAL CHECKS

* Check the engine for the following the items:
* Engine compression
* Improper valve timing
* Intake manifold gaskets, refer to Engine Mechanical .
* Sticking or leaking valves, refer to Engine Mechanical .
* Check the EGR operation for being open all the time. Refer to EGR System Diagnosis . See: Computers and Control Systems\Testing and Inspection\Component Tests and General Diagnostics\EGR System Check
* Check the intake and exhaust system for casting flash or other restrictions. Refer to Engine Mechanical .

FUEL SYSTEM CHECKS

* Perform a fuel system diagnosis. Refer to Fuel System Diagnosis . See: Computers and Control Systems\Testing and Inspection\Component Tests and General Diagnostics\Fuel System Diagnosis
* Perform a fuel injector coil test. Refer to Fuel Injector Coil Test . See: Computers and Control Systems\Testing and Inspection\Component Tests and General Diagnostics\Fuel Injector Coil Test
* Perform a fuel injector balance test. Refer to Fuel Injector Balance Test . See: Computers and Control Systems\Testing and Inspection\Component Tests and General Diagnostics\Fuel Injector Balance Test Procedure

ADDITIONAL CHECKs

* Check the EGR gasket for a faulty or loose fit.
* Check the EGR Valve operation for being open all the time. Refer to EGR System Diagnosis . See: Computers and Control Systems\Testing and Inspection\Component Tests and General Diagnostics\EGR System Check

 

[99Yuk]

My bet is on sheered Distributor Gear Teeth. I know, I just went through this before the new motor. Same symptoms. And I know how it happenes too. Buddy was driving it like it wasn't his. Tromping it at every light. That's how mine sheared. Stomped on it, and got up to 80kph, then nothing, it just died on the spot. Same flooding, backfiring as you. Needless to say, I don't do that any more on my new motor. Just saying, it's probably the dizzy gear teeth, which means buddy was abusing your rig.

 

[SunlitComet]

I want to check mine but I am not taking anything apart until I have my diag interface to realign the timing and get some live data feedback. I am tired of other mechanics giving me different explanations as what codes show up.

 

[ezdaar]

It's simple, it jumped time .
On a 145k 5.7, first thing I would do is pu a timing light on it and watch
The timIng marks closely. If. The mark wobbles back and forth constantly it's your timing chain.

5.7's are notorious for wearing out the chain and gears and jumpin time.
Buy a dbl roller timing chain. They like 30-45$ and you caneSily replace it in like 2 hours.
A 14, 10 and 12 mm socket wrench, pry bar and 3 jAw gear puller.
I've done so many it's ridiculous. You will need waterpump and timing cover gaskets aswell.

 

[nokuy97]

Problem is that it won't run at all to check the timing.

---------- Post added at 03:56 PM ---------- Previous post was at 03:52 PM ----------

Would a weak coil cause the same problems , say the spark just ain't there to fire the fuel enough ?