roadrunner_70

Backfired through TBI once. It seemed to run okay after but thought I'd change the plugs, wires, distributor and rotor. I just bought this truck a month ago for the winter. Existing wires were on backwards(plug end on distributor), and I couldn't believe it, but the wires were mounted wrong on the distributor (5,6,3,4,1,2), starting from the normal #1 position. I installed the new wires in the proper order (1,6,5,4,3,2) starting from the #1 positon (approx. 5 o'clock position on distributor). Truck ran really rough, missing, backfire through TBI when revved. Returned wires to original order, same thing. Then checked timing, using timing mark on crankshaft at 0 degrees, lifted distributor cap, and noted position of rotor. It was near the #1 position. I got the truck started and timed it to near 0, after removing the EST wire on the firewall, but still runs like crap, after reconnecting wire, resetting computer. No engine codes showing. I'm stumped! Has the timing jumped? Is it fuel related? Perhaps the fuel pressure regulator. I've changed the fuel filter since I got the truck. Old plugs turned black very quickly once I started this. I'm looking at a dealer trip in two days if I don't solve this. Checked coil with multimeter and it checks out. There is good spark at each cylinder.

broughy84

take the cap off and the number 1 spark plug. Run the engine to TDC. note the location of the rotor. This will tell you weather the distributor is in right or it is 180* off.

The wires were wrong and it ran right????

__________________
Matthew Brough
1998 Chevrolet Venture -- 104,000 miles
1988 Chevrolet Silverado -- 156,000 miles
1996 Chevrolet Cheyenne -- 107,000 miles

roadrunner_70

I'm factoring in my own human error...I might have mislabelled the wires when I took them off. Nonetheless I did put them back in the right order eventually. Could backfires through TBI have caused problems in EGR, or TPS, or other areas?

roadrunner_70

Checked rotor position at TDC and it was right where it should be. Vacuum checked and it seems normal (solid reading at idle, drops on acceleration to about 5 then shoots to above idle reading). Anything more than a slow movement on the throttle brings a backfire through the throttle body. Exhaust smells like sulphur when it warms up. Engine has a pronounced lope or miss.

rpreston

Could be still off 180. Need to make sure your on the compression stroke for setting the distributor. Pull plug from no. 1 cylinder. Pull cap off distributor. Hold your thumb in the empty no. 1 spark plug hole. Have someone bump the ignition slowly. When number 1 cylinder hits the compression stroke, it will blow your thumb from the hole and timing mark should be close to TDC. Move crank by hand forwards or backwards to timing mark. Now check to see where the rotor points to as compared to the cap. With what you've described, its sounds like someone could have put the distributor in wrong and then moved the wires to match instead fixing problem. You could also have a plugged up cat if your getting a rotten egg smell from the exhaust. That'll make it run god awful too. Good luck!

__________________
[SIZE=3]"How do you feel about Women's rights?" " I like either side of them."[/size] - Groucho Marx

Fireplug

Check the fuel pressure you might have been chaising a ghost

roadrunner_70

Thanks for the posts. I'm taking it into the dealer tomorrow since my mechanic is too far away to drive the way it is. I'll let you guys know the verdict.

cf1

roadrunner 70.. what was wrong with your truck? i have a 93 cheyenne4.3 new cam lifters all new sensors and new dist. does exactly as your truck. did you ever get it fixed??

roadrunner_70

I still can't believe it, but after $200(2hours labor), they told me that two wires were crossed. I was spent trying to solve this on my own, and am willing to accept that under the -14 celsius conditions that I was working under, that I might have consistently misread the wiring through the loom. It has been running fine since. If you've just replaced the cam as you've said, the lifters need time to pump up, and it'll run like crap. I found this out recently when I had the valve seals replaced. Make sure you're timing chain's installed properly, and that the marks on the sprockets line up according to the manual. Other than that, you might consider your valve adjustment. It depends on whether your rocker arm studs are pressed in or screwed in. Pressed in are adjusted like so: Mark on crankshaft damper at "0" mark on timing cover. Engine in the #1 firing position. In this position you can adjust; Exhaust valves 1,5,6. Intake valves 1,2,3. Back out the adjusting nut til lash is felt then turn in til all lash is removed. Rotating the pushrod while tightening the adjusting nut.When all play is removed turn one full additional turn to center the lifter plunger. Turn the engine over one revolution(#4 firing position), and adjust: Exhaust valves 2,3,4. Intake valves 4,5,6. There you have it. Hope this helps. Golden Rule: start with the easy stuff first.

cf1

thanks for the fast reply... i took the truck to the garage and was told it was fixed the mechanic said he timed it and adjused the rockers,, i drove the truck less than 1/4 mile and had to return to the garage it wouldnt take fuel and kept back fireing, the mrchanic said he will look at it again but it has him stumped... i think its in the throttle body pessure regulator.. ill let you know..