94 Lumina backfires through throttle body

[leicam45]

I own a 94 Lumina APV, it has 163,000 miles, recently stalled and wouldn't start, taken to mechanic and later after being able to start van, developed severe piston slap and extermely loud lifter noise, now the van backfires through the throttle body upon acceleration, and when cruising along at any speed attempting to accelerate or climbing any grade will bring on severe clatter from the engine and no power, almost as if the timing is out, and it backfires constantly through the acceleration, took it to another mechanic he said the oil pump was faulty and replaced it, this did nothing to cure the problem, he also said that the engine threw a rod or something to that effect and the engine was shot, but I can get it going to 80MPH, it takes a while even with all the clattering, had a code pulled on it and a code 54 low fuel pump circuit voltage came up and it is running real lean. I am not going to dump a motor if it is something that can be repaired for about the same cost. Also had a problem with disappearing antifreeze, never could figure out where it would go, the temp would spike up I would add antifreeze and again it would disappear no white smoke or milky oil though, could all these things be related somehow?? any help or suggestions would be appreciated Thank You

[NeonKnight]

fuel pump is bad, the code shows you that, along with the fact that you are running lean. stop driving it and replace that fuel pump. as far as antifreeze you might have a leaking radiator. i remember something about the 3.8 about a weird antifreeze leak, where it pools up somewhere on the engine and burns off.

I am assuming this is the 3.8 litre V6 im sure all the APV vans had those. i highly doubt the engine is shot, you just done have the fuel to run, and the car is missing and backfiring because of that.

[corning_d3]

Backfiring thru the intake and a severe loss of power, actually all your symptoms point to slipped timing..

[leicam45]

Thank You for the info, this is a 3.1 with throttle body injection, someone told me that the antifreeze leak could be from the intake manifold??
I don't know how to verify that the timing has indeed slipped, I have a timing light but am not sure of the procedure for this vehicle.

[corning_d3]

Just hook up the positive and negative clamps to the battery, and the pick-up clamp to the number 1 plug wire. Start the engine and let it warm. Your timing specifications will be on the emmisions label under the hood. As far as the antifreeze leak.. I also have a 3.1 ('96) and it used a slight amount of coolant too. I eventually found that my thermostat housing was seeping (poor engineering) but never running on the ground. If you find no leak here, try inspecting the freeze plugs in the ends of the heads. These tend to leak sometimes. Let me know how the timing check went..

[jeffcoslacker]

Originally Posted by corning_d3

Backfiring thru the intake and a severe loss of power, actually all your symptoms point to slipped timing..

Yup. Your timing set ist kaput.

New chain and gears time. If you roll the engine one direction with a breaker bar on the crank, then have someone watch in the oil fill hole as you roll it back the other way, I bet you get 10-12 degrees of crank rotation before the valvetrain begins to move, it's so slopped out.

Any more than about 2-3 is replacement time.

[botteman]

Originally Posted by jeffcoslacker

Yup. Your timing set ist kaput.

New chain and gears time. If you roll the engine one direction with a breaker bar on the crank, then have someone watch in the oil fill hole as you roll it back the other way, I bet you get 10-12 degrees of crank rotation before the valvetrain begins to move, it's so slopped out.

Any more than about 2-3 is replacement time.

I have the same symptoms - rattling, sputtering, loss of power, especially with more throttle ... and now it won't start - on my '90 APV 3.1. It just died last week with code 43. And now the TBIs are dumping way too much fuel into the engine while cranking.

Just how does one tell precisely when the cam is moving while the crank is being turned a mere 3 degrees? Surely you don't expect to see or feel it?

[leicam45]

Heloo sorry I have not responded sooner, I ended up taking the whole top end of the motor apart, Intake, heads etc... I am awaiting parts to re-install, I found that apparently the lifters had collapsed, this vehichle had lost oil pressure and the oil pump was replaced, one of the pushrods was embedded into one of the valve lifters and cannot be taken out, I found upon removal of the Intake that 8 of the 12 lifters had run dry and the retaining clips to hold the pushrod seat were missing and these seats were flipped up allowing the pushrods to slide directly into the lifter some of the pushrods had grooves in them from becoming stuck in between the lifter and the seat. I hope that since the oil pump has been replaced and that after I install and replace all these (all new pushrods and lifters) that this cures the problem, I also noticed that the anti freeze looked like coffee with just a touch of milk, the intake gasket was toast. I am now lookin for a diagram for the vaccuum line to this vehicle any help there would be appreciated you can email them to me or tell me where to look. Again thank you for all the resposes they were quite helpful in troublshooting but the vehicle eventually just wouldn't move without some effort and lots of luke to go 10 feet. Thank you and sorry for the long thread I just hope that this can help someone else out there. If your engine runs dry and the lifters don't get oil they will collapse and the pushrod will eventually either break or drive into the lifter via the pushrod seat. Gonna flush the block found lots of crud under the intake add seafoam and Marvel Mytery oil run about a week and dump oil and filter and do all fresh iol and filter gonna flush colling system as well hope this hels someone else.!!!! Good luck everyone needing help!

[botteman]

And I finally discovered my problems... After a month of work on it, the shop replaced the electronic computer module (which was causing the flooding), the timing sprockets and chain (which had jumped eight teeth on the sprocket), and the distributor (which I'm told had a bad circuit inside it ... don't know what it could be). It's now running better than it has in years! Today it turned over 424000 miles. Botteman

[leicam45]

Thank you for all the help, I am almost completed getting it all together, I have the heads back on and the push rods and lifters, I also have been delayed by the snow we got today, we really got walluped, now I just need to know what the torque settings are for the heads, rockers, and intake. I also think that I should replace the timing chain before I button up everything, is this difficult to do?, would this be a good idea or do it only if I need to?? Again I thank everyone that posted help.

[corning_d3]

To replace the timing chain and gears, you'll need to remove the timing cover/waterpump housing and the crankshaft pulley. If it's a high mileage engine, it may not be a bad idea and it's fairly easy to do with a good book and the right tools..

[leicam45]

Hello again I need some help again I have everything back together, less the valve covers, I wanted to start it up before putting them on I can't get any help on torque settings for the rocker arm nuts, this is a 3.1 with the lifters that have the bottom 3/4 of ths lifter ground down, for added lubrication, nobody even the dealership can help with this torque setting, I could really use some help on this one, I tried to torque the rocker arm nuts to the last suggested setting of 13ft. pounds and this bottoms out the lifter, and the van won't start, it just floods the throttle body with fuel and if it sits for a while and I try to start it it backfires through the throttle body. Please someone help!!!!!!!!!

[maxwedge]

Can we assume you knew there are 2 different length pushrods.

[richtazz]

Like Max said, did you put the pushrods back in the proper locations? The intake and exhaust push rods are different lengths, and may be your issue. Because your van has the distributor engine, it may not be a "zero lash" design. Also, in order to set the static timing, you need to ground the EST circuit to disable the ECM from adjusting the timing until you get the timing set. Check your underhood emissions label for the location of the EST ground terminal wire, as the location differs from year to year. Failure to ground this terminal will make initial timing impossible to set, and throw off the entire advance curve.