95 K1500 Ruff Running & Intake Backfire

[CARDOC340]

I have a 1995 chevy k1500 pickup with 350, it is running ruff when driving or idling in gear, and has a intake backfire when accellerating.idling in park is fine. compresion test is fine in all cylinders. replaced cap, rotor, plugs and wires. replaced ignition module. replaced timing chain and gears. replaced fuel pump and pressure regulator. replaced cat. converter and o2 sensor. there are no codes. can anyone point me in some direction. help.
thanks

[bigj-dog]

I had a truck with this condition and the cam was worn out, but if your compression is all high enough and w/in 10% of eachother then I'd lean towards a vaccuum leak, causing a lean condition (no pun intended). You might also consider installing a new tbi base gasket.

[CARDOC340]

there is also a strong of gas coming from the exhaust when running.

[2000CAYukon]

Originally Posted by CARDOC340

there is also a strong of gas coming from the exhaust when running.

What is the fuel pressure?

Are the injectors leaking or do you have a nice cone pattern from the spray?

Unfortunately, it is hard to check the fuel pressure regulator for leaks since the vacuum source is internal to the TBI. A fuel pressure test may help determine if it is leaking or not functioning.

Check the vacuum line to the MAP sensor and make sure the MAP sensor holds vacuum (need a vacuum pump).

With engine off, apply vacuum to the EGR valve. It should hold vacuum. Apply 20 inHG and then start the engine, the vacuum should drop to zero.

//2000CAYukon

[jocat54]

You might want to pull the valve covers and check that all the rocker arms are moving

[fuzzypuppy]

I can lead you to this, there seems to be a problem in your valve train that is produced under load.
Your compression test is a good sign but cannot speak to your problem "as you have learned" because your problem happens under load.
One thing to keep in mind is, if your valve train is working properly it is impossible to get backfire up through your intake, this because your intake valves are closed for combustion.
If your cam is worn your valves may not open fully and cause the rough running but does not explain the backfire,
a burned valve would explain the backfire and rough running but would show on your compression test,
Sticking valves due to wear or bent valves and/or weak valve springs would explain every symptom you gave including un'burnt fuel smell in the exhaust because without proper compression your not getting proper combustion.
If you sit and think about all the symptoms with the one big key of backfire through the intake under a load, valves are the only thing that makes sense.
A vacume test will help in your determination of this, it's the only way to test for sticking or bad valves under a load.
Good luck, hope this helps.

[sreve]

i'm with fuzzy puppy on this. one exception to it (if your valve train is working properly it is impossible to get backfire up through your intake, this because your intake valves are closed for combustion.) is ingnition timing, but it's got to be way retarded.
cams that are damn near round can show some decent compression numbers cranking. doing a cylinder cut out test remove a plug wire at a time while brake torqueing could tell you which cyl to look at. problem is most likely on the exhaust ie: cracked rocker arm, they like to break on the bottom. busted spring. flat cam.
hey
fuzzy puppy you are also correct. i am am not trying to start a pitching war
peace.

[pop826]

Try Distributor Pickup Coil My 93 5.7 Was Doing Exact Same Thing 12 Bucks An 3hrs .it Worked 4 Me Good Luck!

[Elbert]

if no other issues.... backfireing through the intake is a classic sign of camshaft issues, assuming no other problems.

[mrbee]

Check and see that your valves are set properly.

[97cavalier]

is it all in time? don't retard it to much nor advance. But the way it is running you might want to advance it a tiny bit.