odee

I have a buddie with a 283 that has a tbi on it in a jeep. He he put a body lift on it in the process the distributor got broke so it was replaced with the msd unit. The motor backfires thru the tbi now. Could the engine be out of time or has something else go wild on this thing?

snflupigus

could it have something to do with the ecm controlling timing and now he has replaced it with a dist that is not computer controlled?

Therefor the ecm is giving only so much gas assuming a certain timing and now that certain timing is no longer there because it has no control over it?

We need more info.

NJ SPEEDER

if that is the onlything that has been changed then it is a sign that the timing is severly out of time. the only two ways to make the engine fire out the top are for the timign to be way early or the fuel to be very lean.
does it do this at idle? what reved? hard start? run rough?

later
tim

odee

the engine has the complete setup from a 88 model truck on it using computer to control timing. We swapped plugs, wires, coils,cap &rotor same problem. It will idle good then when you give it gas it spits back thru the tbi. We set the time to 0 like the trucks set to same problem. Timing was about 10 degrees before tdc before we reset it. Could the engine have a burnt valve or a intake valve trying to stick and hang open? The problem seems to get somewhat worse as the engine warms up. Thanks for the help, he is wanting to ride this thing on a jeep ride soon so any ideas would help me alot.

iroc22

Backfiring through the intake is usually the sign of a bad ESC, or timing way off.

91Bird305

Mine did that and I checked my timing and for some reason it was retarded 4 degrees! I never even messed with the timing before then so I have no idea what could have caused it. But I set it to 6* now and it is running fine.

TBI305Camaro

you have to disconnect the EST when you time our cars (or TBI units for that matter) i found if you turn it to 6 degrees with the EST hooked up when i turn the car off and back on its retarded about 6 degrees...disconnect it then bump it up (im running 93 octane) and then rehook it and restart the car and it will be at like 20 degrees...sounds like alot to me but i guess the computer has an idea of what its doing at least i hope so

odee

we reset timing to 0 on the engine was running about 8-12 degrees before tdc. We unplugged the tan wire going to the distribitor reset timing same problem. Put in new set of plugs and swapped plug wires out with another set. Could it be the knock sensor is pulling the timing back to much? I don't know to much about the bottom half of the engine, I was told that it has forged pistons in it. I have the knock sensor mounted by the oil filter the headers wouldn't let me mount in the stock place. What about the camshaft are the tbi engines really sensestive to cam changes? How much vaccum should it be pulling? Could the engine have a burnt or not seated intake valve? Sorry for so many questions this is just driving me insane. I'm goning to try the esc this evening, hopefully that may fix it.

JokerRS

Double check the spark plug wires for firing order. Might of cross wired it when putting on the MSD. Its easy to mix up #5 and #7 when your in a hurry.

odee

rechecked timing and the plug wires for the 5th or 6th time. Today got the new cooling fan wired into the jeep and mounted. Unplugged the knock sensor and the engine runs fine no backfiring thru the tbi. So could the knock sensor be bad or could it be the way it is on the motor? Does it have to contact a water jacket to work right? I think we will leave it this way for know the when his trip is over check things out again.

Snowdog 91 Formula

Your timing is way off. Mine backfired and protested all the time. Another thing you can check is your fuel pressure. It might be a little high (or low) depending on your idle.

JuGrNuT350

Me & buddy just put my engines back together and, mine backfires fuel back up through the TBI, we're going to keep messing w/ the timing & check the distributor, I'll check the firing order again... Is there anything else I should check, engine was running fine when we took it apart to do the cam swap

Thanks,

-Timbo-

snail988

I am having the same problem with a 350 tbi in a truck. The fuel pressure is steady at 10 psi, but drops off quickly. The timing I have adjusted several times properly, but I don't have a light so I don't know where it is at. It won't run with the brown wire disconnected. It will backfire alot when it is. It stumbles at any quick throttle and gets worse when it is hot. Actually the problem is barely noticeable when cold. It is showing knock just pressing the gas in idle at like 2k rpms. Compression test shows all cylinders at 150. I was thinking a crack in the head, but I don't know why that wouldn't have shown up in a compression test. Any ideas?

Thanks

Mike Gloff
mgloff@hotmail.com

JuGrNuT350

We got my truck running right last night...guess our tired @$$e$ stabbed the dist. 180# around, so we re-stabbed it & played w/ the timing up to 4# adv...I'm going to bump that up a little more, I have a small vacuum leak just a slightly frayed vacuum hose, we had to reroute my vacuum lines & just to be safe JB welded a hole on the back of the TB, my MAP sensor is just kind of hanging by the TB because the vac. hose was too short but I'll get a longer one tomm...I don't have a FP guage right now so I'm adj. the pressure a little at a time seeing what runs best but I'll be sure to not go to high. I need to start burning my own chips & get a FP guage but it runs real good, got quite a lot more power especially on the low-end & sounds bad @$$.

-Timbo-

Snowdog 91 Formula

Your cam sounds similar to mine. You might need to bump up the idle to around 800 rpm so your stock computer won't freak out on your engine.

dimented24x7

iTrader: (2)

i think the older computers had the timing curves set to 6 deg. BTDC. Try that and see how it works. My 88 camaro was set to 0 deg. BTDC and it did the same thing.