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Dodgerench
Dodgerench, ASE Certified Technician
Category: Dodge
Satisfied Customers: 3407
Experience:  30+ years Dodge/Chrysler exp., ASE Master with L1 certification. Driveability/ combustion specialist
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This question is !! I have a intermittent problem with a

Customer Question

This question is for dodgerench only !! Hi I have a intermittent problem with a ramcharger 1992. It looks like a missfire on some cylinders. Most of the time it does it when the motor is cold at 2000 2500 rpm but it continues to do it randomly when the motor is warm ( every 15 to 30 min). When the trouble happens, I accelerate , I can hear some back fire and I look like a guy who is learning to drive with a manual transmission. I changed the spark plugs, the wire set, the pick up coil, distributor ,the crank sensor,the ignition coil, the m.a.p. sensor and I checked the fuel pressure, 37psi. I verified the injection timing with a noid light, was ok, I cancelled the egr valve and the vaccum selenoid. I also tried to unpluged the oxygen sensor and it made no difference. I dont have any trouble code, I pluged a scope on the crank signal and it seems ok.
Can you help me please
Submitted: 1 year ago.
Category: Dodge
Expert:  Dodgerench replied 1 year ago.

Hi, this is Ed. Welcome to JustAnswer!.

Bucking as violent as you're describing makes me think you have an ignition crossfire or out-of-sync sort of problem. To start, take your distributor cap off and turn the distributor shaft forward and back by hand, making note of the swept area at the tip of the rotor. If it sweeps more than 1/4" (or about 5mm), you'll find that the distributor drive gear and block bushing are likely worn out. This is much more common on the 3.9 (V6) engine than 5.2 (V8), but it happened to both engines in this model year.

Wear causes lots of variation in rotor position when spark is generated and sent to the distributor and cam-crank sync is also affected. I've found that disconnecting the cam sensor -- the pickup plate in the distributor -- after engine startup will eliminate the conflict between out-of-sync signals and if it smooths the engine out under the circumstances you know it acts up, we need to look at that drive gear and block bushing. It's odd, but the SBEC2 engine system on your RC only needs to see the cam signal once and then it can keep count mentally. Removed... it's not noticed, but if the signal is out-of-sync, it causes all sorts of mayhem.

If the rotor swept area is OK, a distributor adjustment is probably all it needs. It's a manual adjustment in this model year, requiring precise crankshaft alignment... but I'll describe that later if needed.

Check it out and let me know what you find. Talk in a bit.

Ed

Customer: replied 1 year ago.
Hi Ed, so i looked at the back lash of the rotor and i have 4 mm and i also tried to unplug the pick up coil and thers no difference ! To do the ignition timing , on the mitchell ondemand 5, they talk about a spécial tool (7558) ( exerciser tool) and i dont have this equipement. Is there another way to make the correct ajustement??
Expert:  Dodgerench replied 1 year ago.

Oooo... your gear's getting sloppy, but we should be able to get a workable adjustment for at least the short term. I don't know what that 7558 tool is, but the good news is we won't need it. All you need are sharp eyes (to read the balancer markings), a digital voltmeter and some hand tools for manually positioning the crankshaft. You never mentioned which engine you have, but I'm going to guess it's a 3.9 or 5.2 Magnum (multipoint injection). If you have a 5.9 engine, disregard everything I say from this point. The 5.9'er is a TBI engine and doesn't use a cam sensor.

What we're going to do is to position the crankshaft so that the V6 or V8 (depending on engine type) mark on the harmonic balancer is aligned with the TDC mark on the timing cover scale -- just like setting timing on an older engine, except we won't be using the easy-to-find slots cut in the balancer. You have to find the one that says V8 if you have a 5.2 engine. For confusion, there is also a V6 marking and since they're etched with a scalpel, they will appear very similar and can easily be mistaken for the other. Your adjustment will, of course, fail if the wrong marking is used. For reference, the V8 marking is very near a heavy-cut slot in the balancer, but the V6 scribe is way off by itself -- no mark near it. Once found, mark it with chalk or something to make it easier to see.

Rotate the engine by hand in the clockwise direction (as you stand in front of it) until the proper mark aligns with TDC. If you happen to go too far, back the engine up a quarter-turn and try it again. You want to stop with all your timing chain and gear slop trailing, not on the forward end. This will compensate somewhat for wear and tear on the entire timing drive system, including the (probably) worn drive gear and block bushing at the back end of the engine.

Now that the crank's set, we just need to adjust the distributor to the switch point of the cam sensor inside.

Locate the tan-yellow wire on your cam sensor pigtail and backprobe it with your digital voltmeter, set to 20 volts DC. Ground the black test lead and probe the connector with the red one.

Loosen the distributor hold-down (13mm) just enough so that the housing can be rotated by hand, but will stay put when you take your hand off and tighten it.

Turn the key on, being careful to avoid bumping the starter and messing up your earlier adjustment.

Now rotate the distributor clockwise a bit while watching your voltmeter. I like to shift the distributor to the right first and make the adjustment to the left because this would duplicate the operating relationship within the distributor as the shaft rotates clockwise. It keeps all slop on the trailing side of the distributor drive as well.

Now rotate the distributor counter-clockwise (left) and watch your cam sensor signal. If it was formerly reading 5 volts, stop when it switches to zero volts. Conversely, if it first read 0v, stop when it switches to 5v. Either one works. The instant signal voltage toggles, stop and lock it down. Once again, if you go too far or just think you could do better, roll the distributor far right and work your way back to the left. Absolute precision is great, but not essential because the operating range for cam-crank sync is ten degrees. I expect we can do much better than that, but that's the window we have to work with.

You'll notice that the ASD and fuel pump relays will fire momentarily as you reach the cam switch point, but it happens only once per key cycle. I no longer use the voltmeter for these adjustments, opting to just listen for the click-whirr of the relays and fuel pump. It's quicker and I don't have to probe any wires that way, but I thought I should tell you the recommended way to do it first.

If you happen to have the 5.9 throttle body injected engine, check to see if one of the two injectors firing in the throat of the throttle body skips a beat now and then. These injectors have historically had problems primarily on cold engines and since you have a pair of injectors, you can compare their actions to each other. They should look exactly the same, so if one skips a beat now and then -- or quits altogether -- it means that injector is bad. They're driven by the same timing signal, so there's no reason why one should work when the other doesn't.

Aaaand that's it. Lock that sucker down and let's see how it runs!

Ed

Customer: replied 1 year ago.
Hi ed, it s a 5.2 l , i did exactly what you said for the timing but still do the same. The only thing is that i have only one mark on the timing cover ( 5-tdc-5) but all the rest was good. I saw the 5.0v on my multimeter and i hearded the fuel pump relay at the same time. When i start the truck , he ad litle dificulty during the crank so i turn clockwise the distributor 1/8" and after it crank ok. What is the next step??
Expert:  Dodgerench replied 1 year ago.

Well, since you had to do a custom adjustment after precisely setting the engine up, I'm wondering if you should continue moving the distributor and retrying it. The crank balancer outer surface might have shifted, rendering those V8 and V6 marks irrelevant. You really have nothing to lose at this point, so continue turning the distributor clockwise until it won't start or runs worse. Maybe we'll get lucky.

Expert:  Dodgerench replied 1 year ago.

Been a while. Any news?