megtom2

This is on my 1989 Formula 350.
Cylinder #3 was dead showing 20 on a compression check so I took everything apart to check out the head on that side. I found a burned exhaust valve that wasn't closing so I change it out. Lapped the valves good and started putting everything back together. Once I was finished I checked compression on the driver's side(one I worked on) and all had 145 compression.
When I went to crank it up it died within a second of running. Only way to get it to run is to pump the gas and if I try to run it around 1k rpm it backfires into the intake.
I changed out the MAF with a brand new one I had sitting around with no change.
I have gone over all the wires and they are hooked where they are supposed to be. Sensors and spark plugs.
Fuel pressure sits on 43 when I turn the key.
Any ideas on what this could be?
Thanks

Midnight 85

Did you check to see if the new valve traveled in the guide freely? It may be hanging up. First thing I would check is the lash setting, maybe you have one too tight. Did you check the pushrods for straightness?

RLG

check the timing/Dist. 180 out?

WW7

My thoughts exactly.As long as your positive the wires are on correctly..WW

CorvetteMike2024

If your timing is correct, and its backfiring thru the intake, could be caused by a lean mixture. Running lean makes your car run hotter. Possibly a lean mixture could have caused your problem with the exhaust valve. I am no expert. Just trying to help. Good luck. Any codes?

megtom2

All the pushrods rolled true and are not even that old. The guides seemed fine and allowed the valves to slide but were not too loose.
When I took out the distributor I had the engine at 1TDC and reinstalled it in the same location. I thought that was the problem also so I loosened the distributor hold down and rotated it back and forth but it didn't seem to make much of a difference. The rotor was pointing to #1 when #1 was TDC.
I got it to run long enough this morning to throw a code 33. Manifold air pressure. Geez, am I going to have to take everything apart again?

CorvetteMike2024

Are your rockers set properly? How did you ajust them? Maybe too tight?

CorvetteMike2024

Ck the connection to the sensor for good contunity. Sometimes the wiring plugs can have corrosion.

megtom2

When I adjusted the rockers the first time I just did the 1TDC/6TDC method since the engine was already at #1 and it is faster. Once I cranked it and encountered this problem I went back in and did the "Feel the exhaust pushro move up, adjust the intake" method which takes longer but is about as exact as you can get. I tightened the nuts until I couldn't move the pushrod up and down but could still spin it then gave it another 3/4s of a turn.

ddahlgren

I would unplug the injector for fun and see if the backfire goes away. Obviously it wil stil miss running on 7 rather than 8 cylinders. Something burned the valve in the first place.

kenmohr

Check your wires. You may have switched them. The firing order may be wrong. If this problem started after your work it may not be major and something you did or missed.

megtom2

I have checked the wires twice and they are correct. I am going to go through it again today. I am starting to think the cam might have a worn lobe. Stinks to be brought back down from being so happy when the compression showed 145 on what had been a dead cylinder.

desertmike1

The fireing order might be correct, but are they "in the proper rotation" at the distributor cap. I have seen this problem many times.

Your symptoms sound like an ignition problem..

SunCr

Sure sounds like the Distributor is off a tooth. Easy enough to do - well at least for me anyway which is why I took a Dremel and made a small mark on the intake to show me where the rotor needs to be. Verify TDC with an appropriate tool so that you can also make sure the hub didn't slip at sometime in the past - and then see where that rotor is in relation to the plug wire. My guess is that's a one over or back.

pcolt94

I agree with the ignition timing theory as stated above several times.

No matter what you could have done wrong, it will run even on 6 normally operating cylinders. The problem is global, affecting entire engine. I think your work is probably fine.

Having said that;
However, I would give a check to fuel pressure. There is also some merit to what CorvettMike indicated in reference to a lean condition. I have seen low fuel pressure do similar things and can cause backfiring also.

Always check where you have been to see what is not connected or got broken.

Calderone

plus , reinstall the dizzy just to make sure !

megtom2

I have reinstalled the distributor. It is spot on or damn close. I did that yesterday and cranked it up. Started then died. Same as before. I did another compression check on 1,3,5 and 7 and they all were 135 or over. Starting to run out of ideas as to why it won't run. At least get it going so I can put a timing light.
Driving me nuts.

Muffin

When you run completely out of ideas back out the 3/4 turn you gave each valve when you did your adjustment. Once I over did my valves, had exactly the same condition you now have.

megtom2

I think the last thing I can try is tightening the valves less. So loose I hearcem clacking. Back in the fall that is about what I had to do to get our 86 corvette to run right.
Argh!

Calderone

i had a problem like that in a 89 Formula, it was a faulty ignition module or coil
we never knew which of them because we replaced both !