new stroker in, but have problems!

[onetallmj]

Well I had a shop put my stroker(4.6) in my MJ and took it home today.
Its a basic 4.6 with the Comp cam and regular pistons( no dish) so the compression is probalby high. Anyway the problem is that on the drive home when the gas pedal is pressed there is a lull and it backfires but if you really give it the gas it goes fine.

I was planning on checking the MAP and all the other sensors to make sure their hooked up correctly. Anything else to check? It idles fine but took longer than normal to start up. Maybe build an ajustable MAP? How can I check the air/fuel ratio at home with no gauge?

thanks

 

[Dr. Dyno]

Check the distributor indexing. It may be a few degrees off.

http://www.angelfire.com/my/fan/dist_index.html

 

[old_man]

Backfire is virtually always a timing related problem. Either spark timing or valve timing. DrDyno is probably correct on the distributor indexing, but since it is a new rebuild, I wouldn't rule out the cam not being timed to the crank. An extremely long shot is the injector drives swapped on the injectors. This normally only causes a small hesitation and rough running, not backfires. Also just as a precaution, check the spark plug wire order as well. The firing order is on the intake manifold.

 

[onetallmj]

Check the distributor indexing. It may be a few degrees off.

http://www.angelfire.com/my/fan/dist_index.html

I read the article(thanks by the way for linking that). Can you pull the #1 spark plug instead of the valve cover or is it too difficult to verify the #1 piston at TDC that way? I always have a problem with the cover leaking after I pull it.

 

[frsno jeeper]

I had the EXACT problem with my stroker.
After reading the FSM AND the haynes, i decided to look at the original motor(i had a donor motor to stroke)and i think i remember that the books were wrong?????
Dont quote me on that though, its been a while

 

[old_man]

You shouldn't have to pull the spark plug or valve cover. You know it is not 180 out since it runs. Just turn the engine over to 0 degrees and make sure the rotor is pointing somewhat towards cylinder #1 and you can be sure it is on the compression stroke. You can then see the rotor position and make any adjustments required.

 

[NHxj4x4]

I just did mine as well, and I timed it correctly (I thought) until Dr. Dyno mentioned the compression/ exhaust stroke thing. Honestly, I'm not sure where my was when I indexed the distributer. I do not want to pull the valve cover (although I will if necessary) so is there in fact a way to look through the #1 spark hole and tell if your on compression or exhaust? Any other way possible w/o removing the VC?

Thanks!

Todd

 

[Cjmartz2k]

Timing notch on the fly wheel?

 

[NHxj4x4]

Timing notch on the fly wheel?

Flywheels not on, my engine is on a stand.

 

[Cjmartz2k]

I ment harmonic balancer--I don't know what the hell I was thinking. I thought when you line that little notch you put a chalk mark on when you doing your timing up to the 0* on the timing scale thingy, whatever it's called, #1 was TDC, but maybe I'm wrong.

 

[NHxj4x4]

I ment harmonic balancer--I don't know what the hell I was thinking. I thought when you line that little notch you put a chalk mark on when you doing your timing up to the 0* on the timing scale thingy, whatever it's called, #1 was TDC, but maybe I'm wrong.

Your half right, there are 2 cycles, compression and exhaust. I stupidly did not check which I was on when I dialed in the timing. I need to see if I can just look through the #1 plug and see which stroke I am on, does anyone know?

Thanks!

Todd

 

[Cjmartz2k]

If your doing it that way, no. You would have to be able to see the valves, which might be kinda hard through the plug hole. How many times does the harmonic balancer/crank spin around in relation to the piston going up and down?

 

[NHxj4x4]

2 full turns of the crank, and you get 1 full cycle, 1 for compression, and 1 for exhaust

 

[old_man]

OK, I will say it once again. If it is running, it is fairly close. It is definately not 180 out. You don't have to worry about what stroke it is on. Turn the engine over to where the rotor is close to the #1 spark plug position when looking under the distributor cap, then look down at the harmonic balancer for the timing marks. Then turn the engine slightly to get it to the timing you will be using for your setup. It will be on the compression stroke.

There is absolutely no need to pull a valve cover or even a spark plug.

 

[corbinafly]

OK, I will say it once again. If it is running, it is fairly close. It is definately not 180 out. You don't have to worry about what stroke it is on. Turn the engine over to where the rotor is close to the #1 spark plug position when looking under the distributor cap, then look down at the harmonic balancer for the timing marks. Then turn the engine slightly to get it to the timing you will be using for your setup. It will be on the compression stroke.

There is absolutely no need to pull a valve cover or even a spark plug.

x2. I agree with old man.

K

 

[NHxj4x4]

x2. I agree with old man.

K

right, I understand all of that, but it's on an engine stand right now, why would I want to install it with the timing f'ed up? If there is no way to see the position through the #1 plug hole, that's cool, just please tell me that, and I'll go take the VC off and make sure I set it right.

Thanks,

Todd

 

[old_man]

Looking through the #1 plug hole. Turn it to where both valves are closed. Bottom line is that everybody makes to much out of this. Just crank it to 0 degrees and index the distributor. If it doesn't fire and start, but instead does a little backfire through the throttle body. just pull the distributor and rotate it 180 and drop it back in.. You have a 50/50 chance and if it doesn't work, its a 5 minute job.

On an engine on a stand, I just put my finger in the #1 sparkplug hole and turn over the engine. If you feel pressure, you are on the compression stroke.

 

[NHxj4x4]

Looking through the #1 plug hole. Turn it to where both valves are closed. Bottom line is that everybody makes to much out of this. Just crank it to 0 degrees and index the distributor. If it doesn't fire and start, but instead does a little backfire through the throttle body. just pull the distributor and rotate it 180 and drop it back in.. You have a 50/50 chance and if it doesn't work, its a 5 minute job.

On an engine on a stand, I just put my finger in the #1 sparkplug hole and turn over the engine. If you feel pressure, you are on the compression stroke.

Cool, there's my answer, thank you Old Man

 

[Dr. Dyno]

You shouldn't have to pull the spark plug or valve cover. You know it is not 180 out since it runs. Just turn the engine over to 0 degrees and make sure the rotor is pointing somewhat towards cylinder #1 and you can be sure it is on the compression stroke. You can then see the rotor position and make any adjustments required.

That's right. Since the engine runs the distributor can't be more than a few degrees off so you can go through my distributor indexing procedure omitting step 3 (the removal of valve cover). As Tom said, just turn the crank until the notch in the crank pulley lines up with the "0" mark on the timing cover. If the rotor is pointing somewhat towards the no.1 plug wire, you'll know the no.1 cylinder is on the compression stroke so just rotate the distributor body until it's in the position that I described and bolt it down.
If the distributor was 180* off, the engine would crank but not fire.