2004 4.7 HO, rough idle only at cold start, advice? - JeepForum.com
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post #1 of 15 Old 03-11-2019, 09:03 AM Thread Starter
JRobes
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2004 4.7 HO, rough idle only at cold start, advice?

Good morning all,

I'm having issues with a rough idle at cold start on my 2004 4.7 HO. Engine shakes pretty bad and then stalls, no knocking noises or anything real bad sounding. If I give it a bit of throttle, it'll push through it after 5 to 10 seconds and then run perfectly fine, and runs fine on subsequent starts shortly after it's been running. Only happens after it hasn't run for many hours (overnight). I have had a previous 02 sensor check engine code, but it went away on it's own.

This weekend I had a particularly rough start, and it gave codes for multiple cylinders misfiring, so I pulled all the plugs right after to check if they were gas-soaked/fouled but they all looked fine. I'm wondering if it's just running lean for whatever reason at startup. I've seen that there were posts on this site suggesting a bad upstream 02 sensor has caused this cold start rough idle issue for others, wondering if throwing a volt meter and testing those is the next step, or possible checking fuel pressure at the rail to make sure that's good.

Things I've done:
cleaned the IAC
checked and replaced spark plugs (all looked good/normal)
tried a bottle of fuel system cleaner for kicks with a full tank of premium gas

Anyone have similar issues or advice on what to chase next?


2004 WJ Overland, 4.7HO, Vari-Lock Axles, 3" OME HD/Bilstein lift
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post #2 of 15 Old 03-11-2019, 09:17 AM
jtec
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get a free scan at an auto part store FREE even if cel is off -SCAN not key trick!!

Check ECT sensor, GIGO if skewed reading.

Check for leaking fuel injector.

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #3 of 15 Old 03-11-2019, 06:22 PM Thread Starter
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Quote:
Originally Posted by jtec View Post
get a free scan at an auto part store FREE even if cel is off -SCAN not key trick!!

Check ECT sensor, GIGO if skewed reading.

Check for leaking fuel injector.
I did get a proper scanner and the only codes were for misfires during that short start-up period if I don't give it throttle and it stalls; the 3 codes I got on that particularly bad startup was P304, P305, and P307 which are all misfires of cylinders 4/5/7. I'll check out the ECT sensor; it makes sense that both that and a bad oxygen sensor on the exhaust could give bad readings to the PCM and cause it to run lean at startup.

2004 WJ Overland, 4.7HO, Vari-Lock Axles, 3" OME HD/Bilstein lift
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post #4 of 15 Old 03-12-2019, 07:23 AM
99sajeep
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Since it definitely sounds temperature related, I agree that the ECT sensor would be first suspect!

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post #5 of 15 Old 03-12-2019, 07:50 AM
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what makes you think o2 sensor is BAD?

I would look at plugs, maybe change time -use correct plug - read plug and post, wet dry,black tan etc.


I think you fouling RICH not lean, both banks -
A SWAG tell us what air filter, what plugs are you using, any engine mods?


bottle of fuel system cleaner - what brand? on a full tank might be a weak 'solution'.

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #6 of 15 Old 03-12-2019, 08:46 AM
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My misfire turned out to be coolant seeping past a failing head gasket between 3 and 5, let's hope that's not the case with yours. I doubt it seeing 4 is affected, if it was just 5 and 7 it's more feasible. A look at the plugs should tell, 3 and 5 on mine looked like they were steam cleaned compared to the rest of them. I had the same symptoms, misfire at start up however I never got a CEL for it.

2004 Limited, 4.7 modded slightly, IRO 3" RockLink LA front, adjustable SA rear, Bilsteins, Addco bar, JKS disconnects. Coming attractions include 242hd, IRO SYE and Woods DS right after the new engine/trans..
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High speed, low drag
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post #7 of 15 Old 03-12-2019, 10:22 AM Thread Starter
JRobes
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Quote:
Originally Posted by jtec View Post
what makes you think o2 sensor is BAD?

I would look at plugs, maybe change time -use correct plug - read plug and post, wet dry,black tan etc.

I think you fouling RICH not lean, both banks -
A SWAG tell us what air filter, what plugs are you using, any engine mods?

bottle of fuel system cleaner - what brand? on a full tank might be a weak 'solution'.
Per my OP, I've had a ECL code for bad O2 sensor before, went away on it's own, hence thinking that *could* be causing an issue still. Not sure though.

I pulled and replaced all plugs with to-spec (and properly gapped) new Champion platinum tipped ones. The old ones looked fine for their age which was around 60k miles. Pics below. Still have same rough idle after all new plugs.

Fuel system cleaner was Redline and I didn't really expected to fix anything except possibly a slightly clogged injector. Per my OP, just did it for kicks.

No engine mods/abuse, just a K&N filter which is clean.

Quote:
Originally Posted by cDee63 View Post
My misfire turned out to be coolant seeping past a failing head gasket between 3 and 5, let's hope that's not the case with yours. I doubt it seeing 4 is affected, if it was just 5 and 7 it's more feasible. A look at the plugs should tell, 3 and 5 on mine looked like they were steam cleaned compared to the rest of them. I had the same symptoms, misfire at start up however I never got a CEL for it.
Agree it's not likely a coolant leak, my coolant reserve tank level has been consistently full/at normal level, but will keep an eye on that too. Also guessing leaking coolant into certain cylinders might cause some plugs to look worse than others, doesn't look to be the case. Also don't notice any change in the actual exhaust smell/appearance which could show if there was some coolant being burned off.

As for the plugs, they looked uniformly wore/dirty so don't think any one cylinder or any valves that is the issue.
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IMG_20190310_161724.jpg   IMG_20190310_161729.jpg  

2004 WJ Overland, 4.7HO, Vari-Lock Axles, 3" OME HD/Bilstein lift
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post #8 of 15 Old 03-12-2019, 11:16 AM
jtec
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HO engine? RC7PYCB4 your ok.

As mentioned coolsnt leaks often give pplugs a clean, STEAM cleaned appearance.

K&N not a recommended filter - yes no MAF but still not a recommended filter.

Is engine reaching corrct temp?

Do you have a scanner showing live data?

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #9 of 15 Old 03-12-2019, 11:19 AM Thread Starter
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Quote:
Originally Posted by jtec View Post
I do not think platinum plugs are correct - Time permitting I will ck. Colleagues may know.

As mentioned coolsnt leaks often give pplugs a clean, STEAM cleaned appearance.

K&N not a recommended filter - yes no MAF but still not a recommended filter.

Is engine reaching correct temp?

Do you have a scanner showing live data?
quoted directly from WJJeeps.com for the HO engine plugs (the ones I have are correct):
"*NOTE on 4.7 HO plugs: Champion RC7PYCB4 (p/n 3340) is the same as Mopar SPRC7PYCB4 and can be purchased for a fraction of the cost that Mopar charges."
http://wjjeeps.com/service/sparkplugs.htm

I just got a scanner from a work friend today and will be reading the coolant temp and O2 sensors both before and after startup tonight. Hopefully I'll find either of those are showing a bad reading and causing the PCM to give a bad air/fuel ratio at startup.

2004 WJ Overland, 4.7HO, Vari-Lock Axles, 3" OME HD/Bilstein lift
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post #10 of 15 Old 03-12-2019, 11:37 AM
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I did find time to check plug number and correct my post- slow but I did look

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #11 of 15 Old 03-12-2019, 11:41 AM
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with scanner I like to see ECT*, MAP, TPS, fuel trims, and o2 sensor voltages esp pre cat in this case.

Being a 04 HO let us know if there is a schraider valve on fuel rail - they made testing SO easy but they did away with them IDK - save a buck.

*when warmed up.

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #12 of 15 Old 03-12-2019, 05:25 PM
Wjcerakoter
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I just made it through a rough idle mystery with my 04 4.7 HO overland. I have some small mods: k&n fipk, hemifever tuner. However, I purchased my wj stock and it had a rough idle that would stall periodically. I started with E3 diamond fire plugs and denso coil packs (I know what wjjeeps says about the plugs, they're fine). Then I had the engine smoked, found 4 vacuum leaks, fixed the leaks, rough idle continued. Had a top down decarboning of the fuel system, intake, valves, and cylinders. Paid for 3 hours of diagnostics and found that bank 1 downstream o2 sensor wasnt acting quite right but wouldn't throw a code. Fuel trim was spiking between 4 and 15! I replaced both downstream sensors and after 3 days of driving, she's perfect. I hope this helps brotha.
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post #13 of 15 Old 09-04-2019, 10:04 AM Thread Starter
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Wanted to post a follow-up to this so it may help others.

Jeep Info; 2004 Grand Cherokee Overland, 4.7 H.O. motor, 130xxx miles, my family have owned since new (and thus has been maintained meticulously, which eased my decision to fix the issue).

Things I checked/noticed:
Compression tested the cylinders: some had readings lower than others, easily over 10% variation.
I was losing coolant but unable to see where. Could slightly smell it in the exhaust, but not visibly see white smoke. No coolant visible in the oil during oil changes.
Pressure tested the fuel rail, had good pressure there.
Checked for leaky injectors at full fuel rail pressure, no leaks.
Noticed the upper rad hose would expand more than typical at the timing cover connection, made me believe excess pressure may be in the coolant system.
Noticed a burning rubber smell if vehicle was left idling once up to temp.
Connected the torque pro app to my ecu and monited major vitals while driving, all looked good including exhaust sensor voltages, coolant temp sensor, and ambient air temp.
Rough idle only happened at cold starts in colder temps. Hardly noticeable in warmer summer months.
Idled low sometimes around 400 rpm, other times fine around 600/700 rpm.

Because of all this, I concluded to check and replace the head gaskets. My timing cover was already somewhat leaking oil, so would hit two birds with one stone. My suspicions were correct: there was visible signs that coolant was leaking into the cylinders past the gasket once I pulled the heads. I also assume pressurized exhaust gases were making their way past the gasket into the cooling system causing the excess pressure I saw at the upper radiator hose. While removing the timing chain guides, they were so brittle they snapped while just unscrewing the bolts holding them to the block so replaced the timing chains, guides, and chain tensioners as well. Obviously also replaced timing cover gasket and all miscellaneous gaskets since my head gasket kit came with all those. I was surprised at how clean the engine internals were after 130xxx miles, but then again we always maintained a close eye on oil and coolant levels and did all regular oil changes. Premium fuel for the H.O. motor probably helped as well.

An oil change and coolant flush later, she runs like a top and no more rough idle. Total cost of parts around $500, and around 3 days of labor (first engine teardown /rebuild so was extra cautious with everything). Not an easy job by any means, but well worth it vs paying a mechanic $3000, and good bonding time with my dad who helped.

Cost breakdown:
Cloyes Timing Chain/Guides/Tensioners Kit: $150
Fel-Pro Headgasket Kit: $108
Fel-Pro Timing Cover Gasket: $50
New head bolts (make sure to order 2 sets, 1 per head): $80
New Oil/oil filter/coolant; $80
New Power Steering Fluid (lose some from hydraulic lines when removing fan/radiator): $10
New upper rad hose: $10

Hope this helps someone in the future.




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2004 WJ Overland, 4.7HO, Vari-Lock Axles, 3" OME HD/Bilstein lift
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post #14 of 15 Old 09-04-2019, 04:24 PM
jserna
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Brother!!! She looks bad a$$!!!
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post #15 of 15 Old 12-25-2020, 05:29 PM
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The only thing I'd have done different than you is replace the intake valve seats. It would have cost you another $1000 but it would have been money well spent to know that those specious cintered metal seats would be gone. The engine will probably be good to 400K with that change.

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