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Engine surging/misfire/hesitation

25K views 12 replies 6 participants last post by  aofarrell2 
#1 ·
Lately the engine has been surging when idling, from 500-1500RPM, constantly, it's worse with A/C on. Also when driving, if it is cold it will knock really bad, and when warm it will hesitate and try to die at any RPMs below 2,000, so I have been running it in a lower gear to keep engine speed up...

So it's mostly a new thing, although it had a slight surging when idling, it got really bad lately. It's on the 2000 GC in my signature. It set codes for misfire on several cylinders, no particular pattern in which cylinders misfired. I tested the ignition coil and determined it to be out of spec, replaced it, and the misfire etc. did not go away, although I noticed a substantial increase in power. I recently did a tune up as well, all of that is fine, all injectors tested in spec. While it never got a code, my scantool revealed a jump around the board from rich to lean, in connection with the surging. Unplugging the IAC does not change it. I'm really at a loss as to what it is, it uses no coolant or oil. I am suspicious it is the catalytic converter, but not sure.

Any suggestions?

Thanks,
Alec
 
#2 ·
That tune up you mentioned, Can you be more specific on what you did/checked? To me reads like a vacuum leak, Has the MIL come back?, check all the vacuum hoses, slowly and carefully, if it is maybe you can hear it with the engine on although not always. PCV valve stuck open? or something like that, that up and down of the mixture definitely points to a vacuum leak.
 
#3 ·
...and using brake cleaner (leaves no film) spray around the intake manifold/plenum gasket with the engine idling. If the rpm jumps or steadies you may have found the vacuum leak.
 
#4 ·
Tune up: New spark plugs, wires, new air filter, new PCV valve, new breather hose, new PCV valve hose, 30-30-30 reset.

The CEL has not come back, *yet*. The MAP sensor reads in spec when idling.

A vacuum leak would make sense. I have replaced the upper intake manifold gasket, perhaps the lower one is leaking?

Any other alternatives to brake cleaner? I don't like the idea of running that through the engine, type I use is non-flammable.
 
#5 ·
That "knocking" still points me to lean mixture, Is your fuel gauge reading full or close to full or perhaps empty or almost empty? I'm asking because in those conditions the computer will not check for leaks in the EVAP system and you can have the EVAP valve stuck open and not have the MIL light up. Also an EGR leak will do that too, I don't recall right now the criteria for the system to check for performance, I'll try to check the FSM and get back to you between today and tomorrow. It has to be a big leak and any of these 2 can be big leaks and not be heard from outside, that is if the PCV valve is good (a new one can be bad) and not fitted backwards.
 
#6 ·
CEL came back today, haven't pulled it. Will check it in a day or two. It is not related to the level of fuel in the tank. I replaced all EGR components recently, helped some with the rough idling. There are no leaks from the EGR system. Both the intake and exhaust systems are coated in carbon, but moreso the exhaust. I'll have to check the PCV valve to make sure it is good still.
 
#8 ·
I'll use propane. Always what I've used. Won't hurt the engine and not terribly flammable.

Pulled the code today. P0304. Cylinder 4 misfire detected. Third time in a row that it's set that code now, but it doesn't set it regularly, but it is the only misfire code, besides multiple misfire, that has been set three times now.

I'll post MAP readings etc. later today, see if I can get it to do the funny things while I'm logging.
 
#9 ·
I think I've finally figured out what is wrong on the 2000 Grand Caravan.

Did vaccum leak tests, vacuum system is good... Ignition and injection timing is proper.

I had my OBD2 interface on it and was logging custom PIDs, noticed I could read torque converter slip. In park, it read almost 200RPM. Something didn't make sense. On the road it dropped to 0.

It finally dawned on me that the engine problems only cropped up after the transmission rebuild, and kept getting worse. Also, the transmission didn't respond to the quick learn I initiated. Guess what? It's the torque converter. Either the T/C is bad, or it isn't tightened. Feels locked up all the time, makes a horrible noise (like a bearing) when accelerating, but the engine is in fine shape, and it misfires, but mostly on cylinder 4 (weakest cylinder). The T/C is causing the engine to be overloaded, causing what the engine is doing! So mystery solved, now I've gotta get it up to the tranny place under warranty. This all explains why I can also spin my tires like I never could before, and why the transmission does NOT shift properly, and also why the TCU and the ECU readings for TPS and Engine RPM read 10-20% differently!

I'll let y'all know how it goes.
 
#10 ·
SOOOOOO your saying that your T/C is responible for the misfire on cylinder # 4????????:blink: i will say that makes no sense, those two systems are not even related, but one thing i have learned is that (do not rule out anything). You have got me interrested thats forsure.look foward to your findings
 
#11 ·
Yep that's what I was saying. I've seen it happedn before.

What happens is the T/C gets out of alignment and either locks up when it shouldn't or puts extra drag on the input/output shafts.

But I took it up yesterday to have the trans checked out, he said it was fine as far as he could tell.

Engine no 4 is missing really bad, so I'm out to do compression check. Any ideas on good values?
 
#12 ·
While I was dealing with a problem with engine stumbling and backfiring on my '99 GC, I read on a few threads here about the flex-plate cracking, and that resulting in the reading from the crank sensor being off enough to disrupt the engine timing. Maybe happened during the tranny swap??
 
#13 ·
Interesting thought, I'll check the camshaft vs CKPS sync values and see what it says, that'll tell me if the flexplate or timing chain are off.
 
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