Ok, so I've been having issues with my 89 backfiring through the intake. First thoughts were timing and ignition system. I replaced the injectors (bosch III's), cap, plugs, rotor, and wires. Everything pieced back together now and went to check and set the timing. For starters, the timing appears to be set currently at somewhere near 25 degrees BTDC and I know it should be somewhere in the 6-8 BTDC range. Problem is when it is adjusted downward, it runs horribly and the backfiring gets significantly worse, to the point that any throttle play and the car wants to stall out.
I've only had the car a few weeks and I'm slowly trying to fix the previous owners mistakes so I can enjoy this thing. Looking things over, I noticed a dent in the fuel rail of the passenger side, will this affect the pressure enough to cause a problem? Any other ideas or suggestions...???

Thanks!

 

other ideas? sure. Worn intake cam lobes or misajusted rockers/lifters. Worn timming gear/chain. Vacum leak. Thats just for starters.

 

Did you pull the control wire to the dis before trying to time it? Computer will advance it to in the 20's at idle. You will find a single wire, round plug almost behind the power brake booster. It must be unplugged. Once you do so, you'll see the timing now much lower and quite possibly where it should be. Adjust your base timing now, then reconnect this lead and let the computer do its job again.

Greg

 

Sandpiper - Did not know about the wire needing to be unplugged. Thank you!

Ok, so reset the base timing to about 8 BTDC and readjusted the idle. Seems to run fine at ide and revs for the most part with no problems. Once in gear, the mayhem starts again... Tons of backfiring and it doesn't want to run. There is a huge hesitation with the throttle. You can coax it into running and getting up to speed, but the problem gets worse as the car warms up (had to run get gas...). When I hit the gas station, it was smoking so up goes the hood, and it puked a ton of oil out of the dipstick tube. Is puked a little before under hard acceleration, but never as much as this.

I have gone over almost every single vacuum line and can't find any leaks. I did have a major leak at the brake booster and that solved a ton of the idle problems I had.

I'm stumped... Anyother suggestions or routes to try?

 

Yeah, follow the directions on the emissions sticker.
The harmonic balancer has been know to slip on the hub. Look carefully at the rubber ring inthe middle.

 

Wow, oil out the dipstick!?! Not good. That may or may not be releated but either way that sucks. Only severe blow by can do that. Between a vent tube (right side cover to throttle body) and the PVC tube (left side to manifold) all but a cracked piston can be vented without building enough pressure to blow out the dipstick.

Take off your oil filler cap and rev the engine up. Any misty looking air coming out means tired rings, outright pressurized high volume air flow means a short block in your immediate future. If blow by is really intense, which will be infinitly worse under throttle then you're stuffing your intake with blow by and oil vapor which will futz power and ability to fire big time.

 

Wouldn't there be signs of oil on the plugs if there was something else going on? It's got to be something overlooked. It's only got 100,700 miles on it, it could be going bad yet... When it does run and you can get into it without it backfiring, it runs great, tons of power and torque. If there were bad pistons or rings, or the cam was bad, wouldn't it affect the overall performance of the car?

 

There would/should be oil on one plug if a piston were broken. Also oil in the tail pipes (dry grey dust is dream come true, dry black dust more like normal and gooey black sime = crying time)..

You can pull 1 sometimes even 2 plugs on a Chevy V8 and hardly notice the change in idle.

That said, do the oil cap thing. Verify air can get through the right side vent and verify the PVC is sucking air and 'clicks' when shaken.

You need to sort out why you blew oil out the dipstick before you care about anything else.. Chasing 2 troubles at once will literally give you a splitting head ache!

 

both PCV valves are operating. There is a slight haze coming out f the oil cap when revving the motor, but not excessive. When I pulled the old plugs, they didn't show signs of anything being wrong. Normal wear and coloration, possibly a little lean, but no oil or carbon buildup at all. Tail pipes are dark, but no smoke or goo in them at all. There's no smoking from the tail pipes when its running either. Nothing I can see that would point to potential internal issues...

 

I did forget to mention that it threw a code the other day after replacing the plugs and such. It threw code 44 indicating a lean condition. Someone pointed to the O2 sensor, but Ive never heard of an O2 sensor causing this many problems...

 

O2 will effect warmed up running only (your issue). If it says too lean, it probably is reading too lean but reading wrong. That will make the computer richen the mixture, maybe a lot, to try to compensate what a bad O2 is telling it. So yes, can certainly cause your miss issues.

The oil out the dipstick though is still really bad. Maybe chock it up to a one time issue and chase your miss first, but if you keep getting oil out the dipstick you have to find out why!

 

I think I'm going to go ahead and replace the O2 sensor and see what that does and work from there. I can keep my foot out of it for a while. Like I said, it only pukes when you're really hard on it. Normally its not too bad, but this one today was pretty bad, which I think has a lot to do with the way its running currently. Who knows, one step at a time I guess...

 

I believe that you need to Start over with rechecking your spark plug firing order.
Something is amiss with ignition timing or the firing order is wrong.

That begins correctly by removing the #1 spark plug.
Have a helper tap - turn the engine over by the ignition key so the crankshaft or front balancer turns in 1/4 turns each time.

Dont forget to unhook the large 10 gauge Pink wire from the HEI distributor if you have the old large car style like my 87 has.
If you have the later small cap distrib., unhook the ignition coil connector or external HEI module.

Stick your finger in the #1 spark plug hole (driver's side very front cylinder by radiator),
Yell to your helper "Hit it"
When you feel a very large and powerful pulse of air rushing out yell "STOP".
You are very close to Top dead Center or TDC for #1 cylinder.
This is what you want!!
Note where the harmonic balancer timing mark is in relation to "0" degrees on the timing tab.
You want this mark as close to ZERO mark as possible if not dead on.
If You overshoot the timing mark,
Have the helper bump the engine over another 2 revolutions.
Do it in 1/4 turn crankshaft revolutions each time.
Makes it easier that way so you dont overshoot the "0" timing mark again.

When you have the balancer at the Zero / "0" mark,
remove the distributor cap.
Note the exact location of where brass electrode is facing or pointing to on the rotor.
Make a relationship indexing mark to the aluminum distributor base.
A RED SHARPIE Permanent marker works great for that.
Now reinstall your distributor cap loose but be sure it is seated 100 % flat and it locates on the locating tab.
Take your red sharpie marker and make a vertical mark on the distributor cap where #1 in the exact location where the mark is you made on the distrib. base.

If the marks line up that's great.
Chances are they wont.
Find out where you put the #1 spark plug wire at.
Move the #1 wire to the closest socket on the distrib cap that matches the red mark made on the distrib base.

Now route the wires in a Clockwise fashion in the exact firing order of your engine.
Its 1-8-4-3-6-5-7-2.

Double check the Ignition wire routing.

Loosen the distributor hold down clamp bolt slightly.

Set the base timing as directed on the tuneup decal on your Vette.
6 degrees BTDC with the engine fully warmed up to at least 190 degrees F and the thin tan with the black trace disconnected( spark timing connector).

Once timing is set, tighten down the distributor hold down bolt firmly to about 30 ft/lbs. Guestimation ok for torque.

Shut off the engine.

Plug the timing connector back together.

Unhook the battery on your Vette.
Negative cable works good.

Turn on the headlights to where they normally would open.
They wont of course.

You are resetting all the BLM's or Block learn values in your OBD1 C4 computer this way.

Connect the battery back up.
Shutoff the headlights.

Start your Corvette backup without touching the gas pedal at all.
Start by ignition key only.
It may take 2 or 3 tries but your Vette will fire up and keep running.
The IAC takes a bit to relearn or ZOOM IN where it needs to be for minimum airflow requirements at startup and engine idle position.

Let your Vette run for maybe 20 minutes, let the cooling fan(s) cycle at least once on an off with full engine warmup.

Don't Rev the engine any.
ECM is relearning BLM's yet.

Shut the hood and take your Vette for a ride and see if matters have improved or not.

If not you have too keep troubleshooting.

I am betting that your Vette will be OK.
And you will be smiling ear to ear with a chitten eating grin.

Brian

 

just for reference, here is a pic of the distributor control wire that must be disconnected prior to adjusting the timing. did you do any other work to the car, and did the problem start after you replaced the plugs, rotors and wires. by any chance, did you adjust the valves?

 

x3 strongly you do nothing until the timing is properly set.

 

87 Vette - Thanks for the information! It looks like a next weekend project... I went ahead and replaced the O2 sensor, just for the heck of it and changed the oil while I had the car on ramps. TONS of oil below...

After the sensor replacement, it runs a little better. There isn't as much backfiring, but the hesitation is still terrible and the motor wont rev all the way up without a struggle. Instead of moving the plug wires around, wouldn't it be easier to just pull the distributor and move the gear around so that #1 lines up where it should in the diagrams? I know I wouldn't be nearly as confused later!

I need to reset the computer again and see if that makes any difference after I replaced the O2 sensor.

 

Thanks! I did find the wire before I saw this post!

 

The rest of these guys posting back to you all have great ideas and contributions to help you also.
The job to repair is still entirely up to you complete and get things right & in working order.

I would buy a new set of spark plugs for your Corvette.
Gap them to factory specifications with a good spark plug gapping tool.

All 8 spark plugs are likely fouled out now.
It makes troubleshooting your car 10 worse yet.

Be sure not to drop a spark plug on the ground.
If you drop a spark plug, throw it away and get a new one.

I say this because the shock of a spark plug hitting the ground may put a near invisible hairline crack in the outer porcelain insulator.
This will cause a new ignition misfire that will make you BATTY/ crazy for a while to troubleshoot why or what is causing the miss.

All 8 cylinders must be hitting at the exact time needed with a hot blue ignition spark across all 8 spark plugs to have your Corvette purring away at idle.
Floor the gas in your Vette and it will Roar to Life with rewarding torque and horsepower to boot.

Brian

 

So many guys dig deep and skip basics. Never over look plugs and wires, so many part throttle stumbles and high rpm misses are just poor spark when it's needed most. You can google it, but you'll find it is harder to make spark in a lean load (part throttle accel) and high rpm (full throttle near red line). This is where bad plugs and wires show up.

If you're familier with resetting the gear alignment, in a heart beat yes! GM HEI's always have the plugs to the drivers side and #1 around from that and when timed right, that plug is almost perfectly to the side. Nothing spells rookie like seeing a plug cocked off at 30d or wires criss crossing the cap. Set right, only 1 wire from each side crosses over and it just plain looks right that way

 

Brian - Thanks again. All the plugs are new to begin with and I cant see how they could be fouled if running in a lean condition. Gaps are all correct and none were dropped. They are the NGK Iridiums. I have had a ton of success with these plugs in other more sensitive motors and I trust them.

sandpiper - All the wires are new MSD superconductor wires, properly crimped and I have gone over them and checked them countless times. I would put money on it that the problem is elsewhere... It has an Accel coil on it, could the coil be bad? I am not familiar with how to test it (or if you even can), but it looks relatively new as well.