knocking and pinging

=3D=3D=3D=3D=3D=3D=3D=3D=3D =3D=3D=3D=3D=3D=3D=3D=3D=3D jroy3@ snipped-for-privacy@jam.rr.com (Big=A0Dope)

I've got a 90 GMC with a 350tbi engine. When I'm driving up inclines or accelerating, I get a ping or knock.

To me it sounds like I've got bad gas, but I've run several different tanks of gas and the problem persists.

Yesterday I got an error code 43 - knock found for 5 seconds. I suspect this might be my advance in the distributor, but don't know how to confirm as the distributor is controlled by the computer. On the old vacuum HEI distributors, I could check the vacuum or advance unit. How do I fix this electronic distributor? Do I replace a module in the distributor or what??? HELP?!? =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D

How many miles are on the engine?

When was the last tune-up?

What do you consider a tune-up?

MarshMonster ~an old horse with a new bridal........is still an old horse~ =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D

you're using '87 Gas, huh?

I changed the plugs, cap, rotor, air cleaner, and fuel filter about 5k miles ago. The engine has 228k miles.

jroy3@ snipped-for-privacy@jam.rr.com (Big Dope)

I've got a 90 GMC with a 350tbi engine. When I'm driving up inclines or accelerating, I get a ping or knock.

To me it sounds like I've got bad gas, but I've run several different tanks of gas and the problem persists.

Yesterday I got an error code 43 - knock found for 5 seconds. I suspect this might be my advance in the distributor, but don't know how to confirm as the distributor is controlled by the computer. On the old vacuum HEI distributors, I could check the vacuum or advance unit. How do I fix this electronic distributor? Do I replace a module in the distributor or what??? HELP?!? ============ ============

How many miles are on the engine?

When was the last tune-up?

What do you consider a tune-up?

MarshMonster ~an old horse with a new bridal........is still an old horse~ ============ ============

yes. 89, and 91 didn't change anything.

Maybe the knock sensor is defective or disconnected

Re: "I've got a 90 GMC with a 350tbi engine. When I'm driving up inclines or accelerating, I get a ping or knock. To me it sounds like I've got bad gas, but I've run several different tanks of gas and the problem persists. Yesterday I got an error code 43 - knock found for 5 seconds. I suspect this might be my advance in the distributor, but don't know how to confirm as the distributor is controlled by the computer. On the old vacuum HEI distributors, I could check the vacuum or advance unit. How do I fix this electronic distributor? Do I replace a module in the distributor or what??? HELP?!?" =========================== I've noticed that a non-functioning EGR valve will cause knocking.This is the first thing to check.Try applying vacuum to the EGR diaphragm at idle and note if the engine RPMs come down and runs rough. Also check that vacuum is being transmitted to the EGR at part throttle by putting a gauge on the line. I would get a shop manual and check it out.It's not difficult.I would fix this before driving too far with that knocking going on.

Krikie!! Probably due for a timing chain and camshaft

=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D Concerning knocking and pinging underload or on uphill grades..... jroy3@ snipped-for-privacy@jam.rr.com (Big=A0Dope) offered this diagnostic input......

I've got a 90 GMC with a 350tbi engine.

When I'm driving up inclines or accelerating, I get a ping or knock.

To me it sounds like I've got bad gas, but I've run several different tanks of gas and the problem persists. Yesterday I got an error code 43

- knock found for 5 seconds. I suspect this might be my advance in the distributor, but don't know how to confirm as the distributor is controlled by the computer. On the old vacuum HEI distributors, I could check the vacuum or advance unit.

How do I fix this electronic distributor?

Do I replace a module in the distributor or what???

HELP?!?

I changed the plugs, cap, rotor, air cleaner, and fuel filter about 5k miles ago. The engine has 228k miles.

(87 Octane ??)

yes, 89, and 91 didn't change anything.

=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D

do this...... (each test drive should take less than 10 min)

Disconect the negative battery cable for a couple minutes.....have a bear. (Clear the Codes from the PCM)

Drive the truck. Downshift to a lower gear when the pinging starts. Stop, Clear the codes again.

Pop a vac line off and let it suck air. Drive the truck. Do the downshift deal again. Put the vac line back on. Stop, Clear the codes again.

Disconect the O2 sensor connector. Drive the truck. Do the downshift deal again. Stop, Clear the PCM codes again.

you could carry this proceedure down the line with all the sensors..... but lets jest start with the above. Darn shame you don't own a lab scope.

Post ALL THE RESULTS.

=3D=3DThings That Would Be Handy To Know=3D=3D

Why didn't you change the ignition wires?

What did the electrodes on the old plugs look like? carboned? oily? burnt? white?

What did the cap and rotor contacts look like?

Is the timeing mark jumping around or is it steady?

Are the O2 sensors carboned up on the ends?

WAS ANY WORK DONE JUST BEFORE THE SYMPTOM SHOWED UP?

Want to know what I would do first????? With a high mileage engine??? With CARBONED plugs???

I would pour me a dose of Marvel Mystery Oil down the intake, while running a 2500 rpm idle in Park.

but....I'm kinda brave, and don't overconcern myself with trivial little details. You may want to get a second opinion on that proceedure. :)

Fact, not Fiction

MarshMonster ~:~