Missing back fire

[Holt50]

asking for help with missing back fire on my 97 gmc Yukon
370,000 miles 4x4 tried new fuel pump and filter no help also there is no engine light coming on. Fuel pressure is 50 to 55 . My next move is to replace plugs wires and cap .
It starts up perfect and ideals prefect and while in drive I can floor it and there is no mud or back fire but when I put her into gear and drive and go it’s horrible missing back fire it’s really got me scratching my head any help would be appreciated.

 

[Holt50]

I meant while in park not drive

 

[iamdub]

Clogged cat?

Have you checked the crankshaft sensor? Pop it out and see if there's any damage to the tip.

 

[OR VietVet]

More Information for DELPHI CV10011

More Information for DELPHI EG10026

What @iamdub said and I would suspect either of these as well. Both of these have passages that need to be free and clear. The IAC helps with load conditions and where either of these are bolted down, there is a passage where the flow needs to be open.

 

[Holt50]

I will check that out tomorrow thank you

 

[Hoesgottaeat2]

Before the parts canon comes out...
Check for excessive play in the distributor by twisting it back and forth. A worn distributor gear caused similar issues in a '98 I had several years ago. A simple swap from a donor 5.7 cured it.
But it may be as simple as replacing the D-cap and rotor here.

 

[Holt50]

yup cap rotor plugs and wires and she is back to normal thank you everyone

 

[Holt50]

The problem is back starts right up a slightly rough ideal can drive it erring until I try to give it a little more throttle then normal and states missing

 

[exp500]

Try a fuel pressure check. Key on eng off, running idle, running hiway.(long hose on guage under wiper on windshield) Also time on leakdown. Fuel pressure spec 60-66#.
Another place to look is fuel trims with scanner. Check steady state hiway. Report findings.

 

[Holt50]

I’ll try that tomorrow thank you

 

[Holt50]

Try a fuel pressure check. Key on eng off, running idle, running hiway.(long hose on guage under wiper on windshield) Also time on leakdown. Fuel pressure spec 60-66#.
Another place to look is fuel trims with scanner. Check steady state hiway. Report findings.

Did fuel pressure test idle running but not driving need to find a longer hose also checked every spark plug with plug tester and all is well there man this is frustrating oh and fuel pressure stayed at52 for awhile before going down 52 at idle and 61 when wide open

 

[Eman85]

370,000mi, stop throwing parts at it. First basic test is a compression test then go from there. Put a vacum gauge on it and see what the reading is, is it steady? Have you had it scanned for codes?

 

[strutaeng]

You either need to invest in a scanner that has live data and watch a few hours on basic diagnostics on YT on how to interpret the data, then look into what has been suggested in previous posts,

OR, just bite the bullet and take it to a real mechanic and let him figure it out.

Unfortunately, the parts changer approach sometimes doesn't work because you may wind up replacing otherwise good parts with (sometimes) inferior parts from the parts store. Now you are out of ideas, out of patience, out of money, you have introduced more unknowns (even new parts are bad out of the box!), and you still have a vehicle that's broken.

 

[exp500]

Did fuel pressure test idle running but not driving need to find a longer hose also checked every spark plug with plug tester and all is well there man this is frustrating oh and fuel pressure stayed at52 for awhile before going down 52 at idle and 61 when wide open

Fuel pressure is a definite suspect, range is 60-66. My experiences are some may miss at 60# slightly.
Put a cheap scanner on it and monitor fuel trims to decide whats next. Fuel pump, relay, oil pressure switch are usual suspects here. Show key on eng off/ at idle /at speed and leak down time 5#.
The Service manual has very good troubleshooting charts.
Look here- https://www.tahoeyukonforum.com/threads/helpful-links.131971/