88 van 350 tbi problems

I bought a 88 van with a 350 tbi.Ill get right to it, i have replaced the fuel filter plugs wires rotor cap oil filter ,there is a knocking in the motor not at idle when i changed the plugs there were 4 wires wrong one that was never pushed on the plug was soaking wet 3 plugs with the gap prong completly gone not even sure how it ran so i thought it was simply a bad spark knock after replacing all and setting the timing just reving it it knocks if i retard the timing and rev it it dont knock but when i drive it it barley goes you get in to it it tries but never has much power while driving i reach down advance the timing it picks up power but realy starts to knock???? What the heck I dont no what to do....


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The rod bearings are most likely worn out. You have a classic case of "rod knock", IMHO.

The crankshaft will need turned or replaced, depending on how much wear has occurred. And new bearings, of course. Rods AND mains.

Sometimes, an unscrupulous seller (or a driver trying to get the last few miles from their ride) will pull a wire from the cylinder w/the knock. This will lessen the knock a little.

You may have lots of carbon build up on the piston cause to have excessive hot spot.

I was thinking of that also as a possibility. You can try seafoam or the old water through the vacuum line trick to see if it clears up. If it is a rod knock it should sound much lower than a carbon ping.

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Chet

hi there,
too much timing advance is detonation knock

check fuel pressure. may be low, IE weak/dying pump.

You mean run it through the gas tank???

[QUOTE=fast68]too much timing advance is detonation knock

check fuel pressure. may be low, IE weak/dying pump.[

Do you have a check engine light on or any codes set? This engine should have a knock sensor. It does sound like you have carbon build up in the cumbustion chambers. Like you said someone had the ign. wires all jacked up so that might have done it. Set timing to specs. Run a compression test to see where it's at. Run high octane gas for now. And like was mentioned pour some seafoam in the throttle body slowly while engine's running and see if that helps.

Ok guys I have replaced the rod bearings and check clearance and shaft looked at crosshatching in cylinders all good added a high flow oil pump.Before this I tried a few other things that the forum told me to like gas pressure is at 10.5 lbs running ran the seafoam thruogh it.Same thing set the timing idles smooth slow rev seems fine get into it it knockes hard as it did before if I pull the plg wire off #3 and rev it it wont knock also if I retard the timing it wont knock???????? HELP HELP

Checked it 10.5psi while running could it be the regulator in the throttle body and can you check that?????

Ok guys I have replaced the rod bearings and check clearance and shaft looked at crosshatching in cylinders all good added a high flow oil pump.Before this I tried a few other things that the forum told me to like gas pressure is at 10.5 lbs running ran the seafoam thruogh it.Same thing set the timing idles smooth slow rev seems fine get into it it knockes hard as it did before if I pull the plg wire off #3 and rev it it wont knock also if I retard the timing it wont knock???????? HELP HELP

I'm sorry if my post caused you to spend time and money wastefully, and a bit surprised that the bearings weren't at fault. They say the road to hell is paved w/good intentions! me><the problem

That said, I would have checked the bearing clearances first before buying and replacing anything- plastigage is cheaper than bearings...

Please tell me you did the main bearings, or at least plastigaged them!?!

Yes I did they seemed fine but wouldnt the motor knock all the time wheather there is a load or not and why can i pull a plug wire drive it up the road and it not knock same if i drive it and retard the timing why does the knock go away.man im lost

About all that's left is a wrist pin or piston slap

Wrist pins can be caused by wear, detonation or pre ignition. You mentioned the wired being crossed up, this could have hammered the piston pretty good.

Piston slap is usually bad when first starting the engine cold and will lessen after it's hot.

A wrist pin will be there all the time.

The sound goes away because the force of combustion isn't happening- so the parts in that cylinder aren't being stresses.

You could try a mechanics stethoscope to see if you can tell if the noise is above the crank, but below the head. With plug wire connected.

cold or hot it knocks the same kinda like a spark knock you now the more you get in to it the louder it gets