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I have info regarding my misfire issues in multiple threads and its time to consolidate it in one place so some sense can be made.
The vehicle in question is a 1999 Dodge Ram 1500, 5.2L V8 4×4 Automatic, with 260,000 miles.
In November I had the plenum gasket replaced with a Hughes plenum kit. This ended about 6 months of misfiring, extreme oil usage, and bad mileage. I got 18 mpg after the fix as opposed to 16 before the gasket went bad, and 11 directly before the repair.
A few weeks later it began performing poorly again. It would knock at idle and flash the CEL under heavy load. I discovered that the wires, cap, and rotor were in need of replacing and this fixed it.
Roughly a month ago, the idle knocking returned. It got progressively worse, to the point of shaking the vehicle in park. I replaced the spark plugs, and this time it got worse instead of better. About a week after, I got a constant CEL with misfire codes for 6 out of 8 cylinders. It almost wants to stall when idling in drive or reverse. The RPM drops from 600 to 400 and there’s an audible “tick” and pronounced shake when it happens, which is every few seconds.
Realizing that the coil was the last old part of the ignition system, I tested it, and it’s within spec. We know this doesn’t mean much though, so I went to the U-Pull-It and got one off an 01 V6 Dakota with 2013 inspection stickers that wasn’t wrecked. (not sure why it was even there) It was the only one out of all the Rams, Durangos, Dakotas, and Magnum-engine Grand Cherokees that I was able to remove. (they all share a coil)
I have not seen a noticeable improvement with the “new” coil. I can’t remove the old coil because the screw heads are stripped, so until I can get a screw extractor, I won’t know how it handles actually being driven with the replacement coil. But at idle, I noticed no improvement.
To clarify, All of my symptoms:
1. Somewhat poor mileage (14 mpg)
2. Knocking at idle in park/neutral, felt in steering wheel especially
3. Shaking at idle in any gear
4. Almost stalling in drive/reverse, with a “tick” sound (like a relay) when it misses and the RPM falls by 200 accompanied by a shake
5. Noticeable exhaust smell inside and out when idling
6. Noticeable dead misses in exhaust note at idle
7. Jolting when TCC is locked up (normal for misfire, as it happened before when plenum was bad)
8. If you spray carb cleaner in the TB, it will run absolutely perfect for a few minutes
9. CEL with misfire codes P0300-307, but not 08. No other codes, and most are pending.Relative compression test sounds good (aka clear flood crank). I have fuel pressure. Coil does not appear to be the issue, but I will know more about that next week. I am not burning excessive oil. (but at 260k without a rebuild, I am burning some, no doubt)
I really am at my wits end here, and I need to get this thing running right. The 4 mpg I’m losing is enough to hurt the wallet, and it isn’t very enjoyable to drive since every time I stop, it shakes enough to drive me crazy and every time I get up to speed it kicks me in the rear.
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[quote=”LJ11194″ post=49221]Yeah exactly. The Hughes plenum kit is rumored to improve highway mileage somewhat but as poorly as this is running, I never expected to even see double digits.
So what does the rapidly changing LTFT mean?[/quote]
From http://www.obd-codes.com/faq/fuel-trims.php
[i]….change in fuel being added or taken away is called Fuel Trim. Really, the oxygen sensors are what drive the fuel trim readings. Changes in o2 sensor voltages cause a direct change in fuel. The short term fuel trim (STFT) refers to immediate changes in fuel occurring several times per second. The long term fuel trims (LTFT) are driven by the short term fuel trims. LTFT refers to changes in STFT but averaged over a longer period of time. A negative fuel trim percentage indicates a taking away of fuel while a positive percentage indicates an adding of fuel.
Think of it like this: You’re driving from the beach at sea level into the mountains. On a short-term basis, you may go up and down several hundred feet at a time as you ascend the mountainous terrain. But, over the long-term, you are actually ascending from low to high altitude several thousand feet, gradually. It’s similar with short and long-term fuel trims. STFT are immediate ups and downs in fuel, while LTFT are what is occurring over a longer period.
A normal STFT reading will generally fluctuate between negative and positive single digits 2-3 times per second. Usually they’ll stay around positive or negative 5%, but they may occasionally go up towards 8 or 9% depending on the efficiency of the engine, age of the components, and other factors. A normal long term fuel trim reading will appear to stay the same, giving a long term average of fuel added. It, too, should be close to zero, positive or negative single digits under normal circumstances. It will fluctuate much slower, possibly appearing static.[/i] (Emphasis mine)
Something isn’t quite right with the LTFT. It should change slower and appear more stable than STFT. This almost sounds as if the LTFT and STFT readings are reversed.
Rereading this thread, I noticed this “….when you floor it and the PCM abandons stoichiometric, it has plenty of power and usually doesn’t miss.”
The PCM is in open loop (not using the O2 sensors for feedback) when starting the engine, the engine is cold, hard acceleration or wide open throttle. From that it sounds as if your miss is mainly happening in closed loop. This says to look at anything disrupting the air/fuel ratio. That means look at the O2 sensors (they’ve checked OK with scanner), air/fuel sensors, or an inaccurate PCM air/fuel map.
When the plenum gasket was replaced for the air leak, do you know if the PCM’s a/f map was ‘erased or reset’? If it wasn’t, that might explain the ‘jumpy’ LTFT. Look in your FSM and if it has a procedure to erase that map, do it. That forces the PCM to ‘relearn’ it’s procedures. Keep in mind that the relearn may take several hundred miles to accomplish.
For a detailed explanation of fuel trims and the A/F map, check out this youtube video from ScannerDanner. It’s about 50 minutes long.
Try to rule systems out and avoid guessing. It’s too easy to check individual components of a system then assume the whole system is working. For example your ignition system. You changed a lot of components but there’s still freak occurrences like a possible wiring harness issue or bad parts (it happens). So before you grab the all clear stamp, pull a spark plug and ground it to see if you do have a good strong spark. Open the throttle to see if the spark stays strong at higher RPM too. Then you can comfortably say that system is good.
A compression test would be a great start. That engine has a lot of miles on it. It has wear. It would be good to try and get an overall feel for the state of the engine. Then you can factor that in when looking at specific systems.
The fuel trims looks pretty good for the most part. How did you get those numbers though? Just with the truck idling? Did you take it for a drive at all then check? Your numbers at least make me think injector problems move down the priority list for now. If you had a significant injector problem dumping in loads of extra fuel then your fuel trims should be considerably negative.
If you don’t have an O2 trouble code and it’s regularly switching over and above 0.45 volts then chances are it’s fine. A quick test you can do is get it into closed loop. Plug in your scanner and set a list of just STFT, LTFT, O2 sensor and maybe RPM. The fewer PIDs your looking at then the faster the scanner will update the numbers. Allow your STFT to settle. It should become close to 0. Then pull a vacuum line creating a lean condition. This should cause your O2 sensor to drop close to 0. It shouldn’t be jumping up and down much. It should stay close to 0. As well your STFT should jump high positive.
Pulling the vacuum line would allow a lot of extra air into the system. The O2 sensor should detect this by dropping near 0 and staying there. The computer then would try and compensate for the extra air by dumping in lots of extra fuel. The STFT jumping high positive. If this happens then chances are your O2 sensor is fine.
You said you were having problems with a clear flood crank. It may sound silly but make sure the accelerator is actually all the way to the floor and not impeded by a floor mat or something. Hook up your scanner and make sure throttle position % is actually 100%.
I really think the timing should be looked at. Do you know the history of the oil change intervals? When it was dropping oil did it ever run low on oil? 260k is a lot of miles on a chain if the vehicle saw serious use. If the chain is stretched/worn then the cams won’t line up with the crank. Put the #1 piston at TDC and check to see that both valves are actually fully closed. Leakdown test would be ideal. Then there’s the ignition timing which could be checked by a timing light. Either one would cause a host of problems similar to what you’re describing.
Avoid looking for a single test that’ll point you directly at the problem.
Thanks for the replies guys.
Funny you mentioned it, I am beginning to suspect the timing because today it got MUCH worse. I have a shake that is much more pronounced than before when the TCC is locked. AND on top of that it’s shaking while accelerating until I get above 1500 rpm. I noticed the tach needle jumping while cruising and when I put a window down I could hear in the exhaust note that it sounded like it was only running on 6, or maybe less. Then later, when backing out of a parking spot, it stalled. When I cranked it back up it coughed and shook before firing. Now, the kicker. Just before I got home, at low speeds and slow acceleration (like moving forward in traffic) I started hearing… I don’t know what. Like a ping sound, but deeper. I hope it’s not a piston hitting a valve…
The oil has been changed regularly it’s whole life. It has run low when it was burning alot, but never below the add area and never for very long. How do I go about checking the valves are closed? I’ve been told before that you can’t check this engine with a timing light because the PCM controls ignition timing.
To avoid being distracted I didn’t check numbers while driving, only at idle. Could the ignition timing advance tell us something about the state of the mechanical timing?
You gotta be careful with live data. Generally you want to feel comfortable that the system is mechanically sound before you put too much faith in the data. Such as the timing advance PID. If there’s too much slack in the chain and the crank/cam shafts don’t line up properly then the input from the position sensor will be false information. Therefore ignition might be occurring a few degrees before or after the computer thinks it is. That’s where a timing light can come in handy. It’ll tell you when the spark is really occurring in relation to the actual crankshaft position and not just when the computer thinks it’s firing in relation to what the computer thinks is the crankshaft position.
Even if you have an electronic ignition you should still be able to hookup a timing light. You won’t be able to change it like an old system but you should still be able to view it. Look for a timing scale above the harmonic balancer. If the plugs are firing too early or too late you’ll get misses. Especially under load. Check it so you know it’s good and you can narrow your search.
If we’re wanting to suspect the chain then sometimes engines have sections of the timing cover you can remove to inspect the timing marks so you can make sure everything does line up. If the crank/cams aren’t synch’d then it could cause a valve to be partially open causing a loss in compression. If you get good results on a compression test then you can generally rule this out. If you want a more accurate test then do a leak down test. Put the piston at TDC and pump some air in it. If a valve is open then you’ll hear the air rushing through one of the manifolds.
You have a lot of miles on that truck. You could very well be dealing with multiple issues. So try not to think about individual component tests trying to find the culprit. Start off with general tests to try and confirm an entire system is working well.
I don’t have access to compressed air, can I check the valves any other way?
Also, OHV engine = impossible to reach timing chain 🙁 I don’t know how to get in there without taking out the radiator and such. I simply can’t reach that far in such a tight space. I know this because the last time I had missing, when my wires, cap, and rotor ended up being the reason, the timing was suspected then too. I don’t have access to a timing light either. I’m fairly new to car repair so I don’t have all these tools that I need to diagnose this.
Also, I think I broke it because now I have a CEL with no codes.
[quote=”LJ11194″ post=49312]I don’t have access to compressed air, can I check the valves any other way?
Also, OHV engine = impossible to reach timing chain 🙁 I don’t know how to get in there without taking out the radiator and such. I simply can’t reach that far in such a tight space. I know this because the last time I had missing, when my wires, cap, and rotor ended up being the reason, the timing was suspected then too. I don’t have access to a timing light either. I’m fairly new to car repair so I don’t have all these tools that I need to diagnose this.
Also, I think I broke it because now I have a CEL with no codes.[/quote]
Hello again, been away from the computer for a few days.
You’ll need air to check the valves without taking things apart.
Yes, on these engines, you have to at least drain the cooling system, and take almost everything off the front of it to reach the timing chain cover. Do you have a guess if the chain & sprockets have ever been replaced.
A CEL with no codes? Have you done a basic battery & charging system test? I’m starting to wonder if your voltages are borderline. The load tester Eric uses in these videos runs about $45.00, you may be able to borrow one from a parts store. Or you could possibly have them run one for you.
The light went away after a day. The battery and alternator are only a year old, replaced together, so the charging system should be fine. I’m getting the front axle U-joints replaced soon and I guess I’ll have the guy do a diagnosis for me then too. I really wish I had the tools and time to keep going here but I can barely drive this truck anymore with it shaking so violently. Thanks for the help everyone. I’ll update you guys when I know something…
My mechanic hooked up his Verus and pulled a code which neither of my scanners did- P0201. He also got P0300 through 307, while my scanners both showed only a P0301. The P0201 lends some evidence to the injector theory, but the multiple cylinder misfires suggest another problem. He suspects either the timing chain (which he confirmed has never been changed, he has done all the work on this vehicle since 2003/30,000 miles) or a crank sensor, which Chryslers are apparently notorious for going bad.
That’s all he had time to do today though, but I thought I’d update this. I should know more tomorrow.
My mother spoke with the guy while I was at work, and she is telling me he said the spark plugs burnt up, which destroyed the wires and the distributor apparently? She might be misremembering/misunderstanding what he said but I’ll know that tomorrow also… Just another update. She also tells me he got it running a bit more smoothly and that he is in the process of diagnosing the original problem.
Plugs 1 and 5 were gapped so wide, they burnt up, which destroyed those wires and eventually burnt up the cap and rotor. He replaced them, and regapped the other 6 to spec. Also put on a new cap and rotor and replaced the entire wire set. (Aren’t plugs supposed to be gapped correctly out of the box?)
It definitely runs better, but I still have a knocking sound and shake at idle and a shake when the TCC locks up although both are far less pronounced. I can hear a dead miss in the exhaust when I listen at the tip.
depending on what plugs you buy.most plug gaps are supposed to
be rechecked before install.I know NGK have always been spot on.
anytime I’ve checked them. Did you ever pull that front o2 sensor
to see if sooted up?No I didn’t. I need to get an O2 sensor socket.
I noticed I can hear air rushing when I have the brake pedal fully depressed, and I do have shaking under braking despite relatively new brakes so I’m back to looking for vacuum leaks in that area. I’m not sure that should cause the miss while the TCC is locked but I believe it could explain the idle missing, correct?
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