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Dodgerench
Dodgerench, ASE Certified Technician
Category: Dodge
Satisfied Customers: 3109
Experience:  30+ years Dodge/Chrysler exp., ASE Master with L1 certification. Driveability/ combustion specialist
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1992 Dodge Dakota: is bogging down and backfiring..warmer..first start

Customer Question

My 1992 Dodge Dakota is bogging down and backfiring When the engine is cold. The warmer it gets the better it runs. When i first start it I can not drive anywhere as there is just no power. What is the problem ? I have had the fuel injectors cleaned, Have tried many gas aditives. Also if it bogs down when i am driving, i can just turn the engine off while i am coasting and then re start it and it runs fine. This will only happen ones it is warmed up. If it is cold it just plain old bogs down and back fires almost every start.
Submitted: 7 years ago.
Category: Dodge
Expert:  Dodgerench replied 7 years ago.
Customer welcome to JustAnswer!.

A couple quick questions...

  • Is this a 3.9 engine?
  • Is the backfire through the intake or exhaust system?
  • Is the backfire on lift-throttle, or while you are accelerating?
  • Have you noticed a clattering noise in the distributor area (3.9 engine)?
  • Do you ever have a CHECK ENGINE lamp illumination while driving?

That'll do for now. Write when you can.

Ed.

Customer: replied 7 years ago.
Hi Ed. Ok i am not sure If it is 3.9 but i think it is. It is the 4x4 LE version with a v6 in it . The Backfire is through the exaust system. and it backfires while accelerating. A bit more info sinse i was just down there warming it up. It can go into the bog down mode without even hitting the gas. It could be idoling then all of a sudden it goes into the bog down mode, and when i step on the gas this is when it does the backfire. I do not hear much clatter around the distributor. There is the odd clatter in the engine but does not seem to be out of the ordinary. The check engine lamp does not come on at all. But the Check oil light comes on when it is idoling , but not when the rpms are up. I have also had the oil flushed and there is new oil in it as well as a new fuel filter and oil filter. The oil light is on regardless of the level of oil.
Expert:  Dodgerench replied 7 years ago.

Thanks, Randy. I'm pretty sure I know what's going on.

You do have the 3.9 engine. Way back in '92 and '93 there were problems with soft distributor drive gears. The 3.9 and 5.2 were both included in the problem, but the 3.9 was over-represented between the two.

Get yourself a Phillips screwdriver and take your distributor cap off. You might need to take the plug wires off of one side (I work from the vehicle left and take that side off) to get the cap up and out of the way. Distributor firing order (clockwise) is 1-6-5-4-3-2.

Once you have a good clear view of the distributor rotor, check it for looseness by trying to rotate it both ways. If you see more than 5/16" of rotor tip travel, the distributor drive gear and block bushing are worn out. Your travel will probably be much greater than 5/16" (8 mm).

This condition and the repair are detailed in Chrysler TSB 18-08-93. Oddly, it says nothing about the driveability aspects, describing it as a noise in the distributor area.

What happened is that the softer distributor drive gear wore heavily in its contact points with the camshaft drive at the rear of the engine. Also, the block bushing that supports the drive gear will be wallowed out, allowing the gear to retreat from the camshaft. Camshafts are never hurt.

All this adds up to a condition where the distributor timing becomes retarded. The rotor tip lags behind where it should be, in relation to the distributor cap. That leads to cross-firing, where the spark jumps to another location that becomes electrically easier... The previous cylinder.

When that happens, you've lost the performance that cylinder normally contributed, plus the air/ fuel mixture is being lit as the exhaust valve is opened by the NEXT cylinder in the firing order. Backfire.

A sensor lives in the distributor, the cam sensor. While it has no effect on ignition timing, it needs to produce its signal within a narrow window of opportunity in relation to the crankshaft position sensor. If they don't fire within that window, the engine becomes out-of-sync and may not start.

If the engine starts, the cam signal is no longer needed to keep the engine running. The odd thing is that an out-of-sync signal plays havoc with the way the engine runs. This is especially true when the engine is cold.

That's because the distributor drive gear does more than just drive the distributor. It also drives the oil pump. Cold engine oil is thicker and harder to pump than later when the engine heats up. During these times, the extra resistance on the worn drive system tensions and stretches all operating clearances to the full-retard position. This is the time when the distributor drive is most-behind in its operation and when it runs the worst.

As a diagnostic aid, you could unplug the cam sensor after starting the engine from cold. If it was acting up just prior to then, it will probably clear up somewhat. Part of the problem is with the cam sync and the other is with cross-firing. Cam sync seems to be the bigger problem at cold engine idle.

You could also rotate the distributor housing a bit to the counter-clockwise position. This would bring both tolerances back into something more like a normal relationship. There is an actual procedure for this, but if you have a worn gear, you'll need to get the gear and bushing replaced anyway and they'll be reset at that time. The procedure is detailed in the TSB.

So just rotate the distributor a bit (if imagining a clock face, make it about 2 to 3 minutes of travel). At that point, most if not all of your driveability should return.

I wish I could tell you the oil light problem would disappear with it, but it seems doubtful. You would need to have your oil pressure checked directly to see what the actual pressure is (could be dangerously low) or you could gamble and just put in a new pressure switch and see what happens.

I'd like to send you the TSB, but I have to confess to being computer-challenged. If you go to the Internet and do a search, I think you could get to a site hosting Chrysler TSBs, if not the Chrysler site itself. TSB 18-08-93.

Let me know if there's anything I can help with, Randy. Good luck with your Dakota!

Ed

Dodgerench, ASE Certified Technician
Category: Dodge
Satisfied Customers: 3109
Experience: 30+ years Dodge/Chrysler exp., ASE Master with L1 certification. Driveability/ combustion specialist
Dodgerench and 5 other Dodge Specialists are ready to help you
Customer: replied 7 years ago.
Thanks a bunch for the info. I will take your advice and check out TSB. One more thing. If i put in a new distributor would this help. Or should i just stick to adjusting this old one ?
Expert:  Dodgerench replied 7 years ago.

I'd check the old one first. They typically aren't hurt by the problem I mentioned. You just need to check the distributor shaft to see that it isn't sloppy or worn. Besides that, there really isn't much that can go wrong with them.

Be sure and write back if there's anything I can help with. Thanks, Randy!

Ed.

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