Diagnose engine misfire problem

This is a Town and Country 2003 van (3.8L). It ran fine then the next day when I started it, it didn't run smoothly. The car shakes a lot. Check engine line came on and I smelt gas. So, I shut down. I read the code and it has 3 codes. 1 code is random engine misfire. The

2nd code is cylinder 3 misfire and 3rd code is cylinder 4 misfire. So, I disconnect batter and replace all the spark plugs with a platinum (2 prongs) spark plug. The service manual says platinum type is the one, but the old spark plug from the car is coper type (I believe, based on the look of it). Put everything back and starts. The car no longer shakes, but the engine is not smooth. I plugin the code reader and get a check engine light is on, but no code. So I press clear on the code reader, which said it can't do that. But read again, there is no code and check engine light is off.

I unplugged the wire to the spark plug of cylinder 4, and plugged it into a test spark plug. Started the engine. Sparks came out of the thing.

Plugged back and I drove around a couple block to see if the problem goes away. Engine still rough, not smooth, and still no code when read. I no longer smell gas.

How do I go from here for finding out what the problem is? What's the most likely cause for this? Fuel system? What would a mechanic do from here?

Reply to
vd
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Reply to
philthy

Take the vehicle out and get it hot, going about 40mph come to a coasting roll for about 20sec and then check to see what the engine fault code says. Chances are the plug wires are bad. The adaptive numerator may have to be learned in order to detect what cylinder is misfiring. and coming to a coasting stop will learn it

Glenn Beasley Chrysler Tech

Reply to
maxpower

I got the check engine light on again. This time, the code is cylinder 3 misfire. How would I go about to trouble shoot this? I am thinking of measuring the resistance of the cord connecting to the spark plug. Is this the way to do it?

Reply to
vd

By disconnecting the battery you erased the learned adaptive numerator memory and all the rest your monitors. Therefore it would not show you what cylinder was misfiring. That's why you should not do a battery disconnect!! More then likely you have a plug wire that is causing the problem. you can either go out and purchase a good set of wires to see if that takes care of the problem or try switching number 3 wire with number 4 wire. If the misfire now shows number 4 cyl misfiring then you know for sure the plug wires are at fault.

Glenn Beasley Chrysler Tech

Reply to
maxpower

Reply to
philthy

Reply to
philthy

You don't need to take the wiper module out to access plugs and wires on this vehicle. Just swap the plug wires and you will more then likely see the misfire went to the other cylinder. DO NOT disconnect the battery

Glenn

Reply to
maxpower

Thanks for the suggestion.

I have swapped the wire, same problem. The same thing happens when I swap the spark plug. The cylinder 3 still misfire. I also put in a brand new Mopar ignition coil. The problem still persist. I notice that after running for a while, when the temperature stabilized for awhile, the misfire appears to be gone.

I even brought to a local shop. They asked me to replace the ignition coil, the spark plug, and the wires, and air filter, and gas filter. I thought to myself, I can do all that. The point is that they must know which is the bad one, and replace/fix that, not just replacing everything. From the test, the wires appear to be good, same for the spark plug. I can't imagine the ignition coil is bad, given it's brand new. So, these mechanics doesn't know what they're doing, or they're trying to fool me.

I took the car back. Now, I want to give it a last shot before bringing it to another autoshop. I want to go by the book. I have the diagnostics book from the manufacturer.

It appears that other problems could be gas related. Some of the steps (about 18) asks me to check the pressure of gas, which means I have to access to the fuel rail (do I?).

The diagnostic book doesn't say this, but I imagine that swapping the fuel injectors would give me some indication too, is that a correct assumption?

I already bought the pressure gauge.

The question is do I have to to take out the upper manifold to do this? How about the lower manifold? Taking out the lower manifold is very tedious. I have to drain coolant. It (the book) asks me to replace the gasket everytime I do this. Sure, I can replace it, but for diagnostics?

Also, if the fuel injector is the culprit, then do I have to take out both manifolds?

Please help.

Reply to
vd

First of all, are you the same person I replied to a month ago or are you just replying to this thread? what engine? Fuel pressure wont cause a cyl misfire on one cylinder!! Go back to basics......you have to have fuel pressure, I assume you do because the vehicle runs and you aren't getting a multiple cylinder misfire. assuming that you have spark on all cylinders because you aren't getting a primary ign fault code. the next step before throwing any other parts at this would be to check compression on the effected cylinder. If I were to bet I would say you have low compression.

Glenn

Reply to
maxpower

I have a 98 caravan with the 2.4l 4cyl. I was getting a random misfire and I put di-electric grease in both ends of the sparkplug wires and that stopped the misfire.

Reply to
jcs444dixmyth

Yes, it's the same me.

The first time I got the problem, use the OBD to read, I got multiple engine misfired, cylinder 3 misfire, cylinder 4 misfire. Now, I got cylinder 3 misfire.

I'll check the compression on the cylinder 3. But first, I have to learn how to do that. Below is for your reference of the steps the diagnostic book said. It applies to all P030x misfire problems.

1) Visual check: worn serpentine belt, binding A/C compressor, P/S pump (I just replaced this a while back, wonder if the rebuilt part is bad, not problem with steering power though), water pump. Misalignment water pump, P/S pump, A/C compressor pulleys. Corroded PCM power and circuits. Improper CKP, CMP, MAP and TP Sensor mounting. Poor connector for CKP sensor, fuel injector, ignition coil, etc. Vacuum leaks. Restricted Air induction system or exhaust system. 2) Ign off, disc ign coil connector, disc the fuel injector connector, ignition on, engine not running, use test light probe A142 ASD relay output circuit at the ign coil connector and fuel injector connector.

I can see the ign coil connector and probe that. I think with just cylinder 3 problem, it can't be this. I don't know how to probe the injector connector as yet. I wonder if I have to take out the manifold(s) to get to that.

3) Ign off, disc. ign wire from spark plug. Disc fuel injector connector of the cylinder being tested. Install a spark tester on the ign wire. Crank engine, observe the tester. 4) Ign off, remove spark plug, visual check spark plugs.

5) Release the fuel system pressure. Install fuel gauge to fuel rail, start engine and observe the gauge reading. (334 KPa +/- 34 KPa)

6) Release the fuel system pressure. Install fuel pressure gauge, start engine until max pressure. Ign off, use clamp to pinch the rubber fuel line between the fuel pressure gauge and the engine. Monitor the pressure gauge for > 5 minutes. Replace the leaking fuel injector(s) if pressure is below spec (400KPa +/- 34 KPa)

7) Release the fuel system pressure. Ign off, connect fuel pressure gauge to fuel rail. Start engine until max pressure. Ign on, engine off, use DRBIII actuate the fuel injector for cylinder misfired. Check for drop in pressure.

8) Check: engine vacuum, engine valve timing, engine compression, engine exhaust system, engine PCV system, torque converter stall speed, power brake booster, fuel contamination, cam lobes, cylinder leakage test, valve springs.

These are a lot of checks. I don't know how to do most of them.

9) Ign off, disc the fuel injector connector, ign on, engine not running. Use DRBIII erase DTC. Use 12 V test light connected to 12 volts, probe the injector control circuit. Use DRBIII actuate the fuel injector. If test light blink/flicker, replace the fuel injector.

10) Ign off, disc fuel injector connector, disc PCM harness connectors. Check injector control circuit for open, short.

11) Ign off, release fuel pressure, raise vehicle, disconnect the fuel pressure line at the fuel pump module, install fuel line adapter fuel pressure gauge between fuel supply line and the fuel pump module. Ign on, engine not running, use DRBIII actuate the ASD fuel system test, observer pressure gauge. Is within 400KPa +/- 34 KPa? Repair fuel supply as needed.

12) Ign off, release fuel press., remove fuel pump module, check fuel inlet strainer for plugged. Replaced if so.

13) Ign off, measure resistance of ign wire. Is it below 10K ohms? Replace if above

14) Ign off, disc ign coil harness connector. Remove the fuel pump relay or ASD relay. Use 12 v test light connected to 12 volts. Probe the ignition coil control circuit. Crank the engine for 5 seconds while observing th test light. If light brightly blink, replace the ignition coil.

15) Ign off, disc ign coil narness connector. Disc the PCM harness connectors. Check the coil control circuit for open, short to ground, short to voltage. Repair as needed.

16) Inspect wire, repair as needed. Replace and program the PCM.

Reply to
vd

compression.

You have pulled this test from a Chrysler Diagnostic Manual and without the DRB it is useless. Perform a compression test on the effected cylinder(s) The only way fuel pressure would affect one cylinder would be a stopped up/inop injector.

Glenn

Reply to
maxpower

The passed weekend was hectic for me. I had to work in the weekend. A few errands turned up. A loss of a family member. I couldn't get this done, other than got my self a real compression test kit (I thought I had one, but it's a fuel pressure meter).

If I have time tonight, I'll do that (besides changing the oil on the other car). I have a few questions though. The factory service manual said to test while hot. This means, I probably needs to take the wiper module off, right? Because I'll get burnt taking out the spark plugs with little space. Is there a better way to do this?

The more important question is that every guide I read, it says if the pressure is low, "squirt" a tea spoon of engine oil into the spark plug and test again. What does "squirt" mean? Like spray with some kind of pressurized bottle, or with a hand lever? I called advance auto parts, and they don't know what I am talking about. I don't think "squirt" means just pour the liquid in. What do DIYers use for this and where do I get it? Thanks.

Reply to
vd

I would do the test on a cold engine just so I didn't burn myself. While you might be a more accurate number on a warm engine in the big picture you are more concerned about differences between the cylinders than the actual number.

Make sure you disable the ignition system and block the throttle open to run the test. Keep the battery charged up so that the engine is spinning at the same speed for each cylinders test.

Just get the oil in there. You can squirt it in using an oil can if you have one available and are able to get it in there. I usually use a piece of clear hose and a funnel... Stick the end of the hose in the sparkplug hole then pour a little oil in the funnel. You want to give it a little crank to distribute the oil before you test again. Basically you have a big empty hole and you just need to get some oil in there.

In case you aren't aware... You put the oil in and test again if you have low compression to test the rings. Oil will help seal worn leaky rings so the numbers go up. If the numbers don't go up with the oil then you have a valve problem or a really big problem with the rings.

Steve B.

Reply to
Steve B.

Thank you Steve. That was helpful. Reading your post, I feel like listening to my older brother in a good way.

The results are in. The compression test passed. Here they are:

Cylinder:Pressure (PSI)

1 : 192 3 : 195 5 : 200 2 : 190 4 : 190 6 : 180

The trouble cylinder 3 has 195, which is within 2.5% of the highest cylinder 5 of 200, and the cylinder 6, with the lowest pressure has

180, which is within 10% of the highest.

This is cold engine test.

So, what could be the culprit here? Is it the bad fuel injector? If that is the case, do I just remove the upper manifold (not the lower manifold) to replace this?

Thanks all.

Reply to
vd

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