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Ask Juan Crespo Your Own Question
Juan Crespo
Juan Crespo, ASE Certified Technician
Category: Jeep
Satisfied Customers: 1523
Experience:  A.S.E. Master Technician, Advanced Level, Emissions - Asian, Domestic, & European
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How much do you charge?

Customer Question

How much do you charge?
Submitted: 1 year ago.
Category: Jeep
Expert:  Juan Crespo replied 1 year ago.

How much do you charge?

You have already made a deposit. That should cover our fee once you accept and positevely rate our answer.

Regarding emails; rules only allow communications through this chat. So go ahead and post those codes and any other data here.

Now, regarding the stumbling issue; are you using a scan tool that can read live engine data? If so, I would need % values for fuel trim (STFT and LTFT) both at idle and at cruising speeds as well as injector on-times (ms) at idle and at cruising speeds. In addition, it would be of great help if you could also safely connect a fuel pressure tester (usually a free loaner from any majot auto parts store) and provide me with actual fuel pressures at idle and at cruising speeds).

We'll continue once I get that information from you.

Best Regards.

Customer: replied 1 year ago.
I had a Solus until it got ripped off. I do not borrow tools -- I repair vehicles. I was using Autoenguity with the Chrysler extension (almost a DRBIII but cannot program, just read and actuate), but it died. I borrowed an Auterra from the next place, but it does not show everything. I ran a fuel pressure test (using GSI tools -- I have the master set and the update) but do not have a dyno (nor access to a 4WD dyno) and I will *NOT* use even a professional attachment to the pressurized fuel system on the road, but I did run at different RPMs. 55 PSI until the evap purge solenoid (under hood) starting ticking (as is normal) and then pressue would drop by 2 PSI (53 PSI) in sync with ticking (I have seen this before). However, I did not do a fuel flow test -- just pressure. I do routinely run a carbon clean (box hooks to fuel injection rail) every 12 - 25 K miles, and I then also use the shop air with hook over sprayer to clean the throttle body. Carbon clean is supposed to clean from the injectors onwards, and the throttle body cleaner is supposed to clean from there through the intake manifold up to the injectors. Engine has no problem starting, idle is stable. We were just leaving for a 300 mile trip when it started to malfunction (warm) on the freeway -- timing advance went to 0 deg and there were rapid small oscillations -- not a smooth trace -- buit I did not capture it correctly. Turned around. Intermitted vanished -- everything seemed fine again. Talking with a retired current California smog diagnosis specialist, I have been told three possilbilities: crankshaft position sensor (CPS) intermittent (supposedly most likely), cam sensor on top of oil pump dirve (less likely), throttle position sensor (less likely as the TPS trace looks normal). The CPS on the 4l AWD is a dog to get to -- even if I release the shift linkage bracket, etc., the transfer case cable is in the way to get my hand up there. The alternative is to gain access through the firewall from the access plate inside the cabin -- but there are lots of things to remove and I would worry about the air bags accidentially deploying (removing dash facia and poking around there). I almost got the TPS connector off -- red lock released, but the push tab did not want to release enough -- and I do *NOT* want to break the connector. Are you guessing fuel injection or fuel injection electronic control? Vehicle has 300k miles -- but it is ouirs and it has run on Amsoil fluids since new -- all drivetrain internal parts seems sound. (Replaced ball-type CV driveshaft joint three times already, rear wheel bearings twice, front hubs, etc., but nothing major -- 42RE "torqueflite" with regular filter changes and band adjustments, etc., regular fluid changes to georotor AWD transfer case, etc.). The problem is *INTERMITTENT* that usually means a loose electrical connector, etc., but supposedly it could be an intermittent sensor.
Expert:  Juan Crespo replied 1 year ago.

I'm a retired Chrysler Master Tech myself, so I sympathize with your situation. I also happen to agree with both you and the smog tech you've talking to that the most probable cause of the RPM fluctuation is either a sensor that fails intermittently (most likely the crank sensor - those sensors were not made at the same place or with the same quality standards the engines were). You talk about your engine having 300K miles; well my friend, we had a Cherokee that we bought new in 1996 through my Chrysler discount and it had over 573K on the odometer when my daugthter traded it in using the Gas Guzzler deal. Never had the head off, didn't smoke and didn't burn any oil. I have also used Ammsoil on all my vehicles.

So, my advice would be to take a very close look at the crank sensor wiring and connector; if that looks good, then replace the sensor itself.

Thank you for sharing your car experience with me. I enjoy hearing from some one who cares about the vehicle they drive. Best Regards.

Customer: replied 1 year ago.
A few updates. There is a TSB NUMBER: 09-003-03
GROUP: Engine DATE: Aug. 01, 2003 that describes carbon build up on the exhaust valves. I hooked up a carbon clean (I own one, along with a OTC fuel injection cleaner that I use a throttle body hook sprayer so that I can use carbon clean MV plus gas through the fuel injector rail and then use the throttle body cleaner to clean from the TB onwards -- not Mopar(###) ###-####D Combustion Chamber Cleaner - 13 oz. Aerosol Can but similar to http://www.motorvac.com/index.cfm?pagePath=TOOLS_EQUIPMENT/FUEL/__ICS_KIT&id=33451). Did this, but now got misfire codes for cylinders 1 and 6, and the MIL light started to flash (severe misfire) during carbon clean treatment and got no O2 sensor traces on live date. Finished the cleaning, buttoned up the system, misfires stopped, no flashing MIL (still evap very small leak DTC and MIL -- waiting for smoker). I then ran an engine vacuum test (hooked up to port used to feed nylon rigid tube that feeds the vacuum reservoir under headlight -- the one that needs the bumper facia to be serviced). Got 18 inches at idle, up to 22 inches as RPM increased. Very very small vibration in the gauge needle (less than a 1/4 inch of vacuum). Did not pull spark plugs to do a pressure balance test -- but usually good vacuum means a mechanically sound engine. Because the crank sensor in a 4WD configuration has more control cables (to the transfer case) to prevent access, I checked flat rate and took it to a chain (Pep Boys) that will install my part -- $150 labor. However, when the technician came out to discuss the issue (graduated 4 years ago from tech school, but does have a California smog certification), and we discussed the symptoms (that did not go away after the cleaning -- started to buck at 65 MPH on the freeway after the engine was warm -- closed loop operation), including 0 deg timing advance, his conclusion is the coil pack rail. Because there is no way to get a test hookup over the boots below the coil rail, no way to scope the high voltage and watch the plug traces. However, the engine does have a valve cover oil leak (small) -- despite the "reusable" "permanent" Mopar gasket -- and his claim was that oil got into the boots cause a spark voltage leak, particularly at higher speed. Note that it does not buck (miss) under load when it is going up a steep hill at 20 - 30 MPH. His guess is the coil pack rail. I also ordered new plugs (just in case -- I use Bosch (4508) FGR8LQI0 Platinum IR Fusion Spark Plug, although OEM was a simple pre-platinum plug. What do you think? The vehicle does not have any of the usual problems associated with a crank, cam, or throttle position sensor -- it has no problem starting, etc. Thanks.
Expert:  Juan Crespo replied 1 year ago.

Well, I tend to agree more with the other smog tech you spoke to previously. A problem with the coil pack rail would manifest itself as bucking and misfiring, especially under load. Another thing that turns me away from the coil pack is that if it had a problem, it would be there all the time, plus it wouldn't affect timing like a crank sensor would.

One more thing, there are tools (albeit expensive) and ways to test that coil pack. The mechanic who said there was no way to test them might not have either the knowledge or the tools to do so.

Best Regards.

Customer: replied 1 year ago.
You want a rating. You have been honest, etc. I will submit one. Here is the update. I found TSB 09-003-03 Jeep 4.0 Engine Running Rough No DTC. I hooked up my Carbon Clean, ran MV-4 through the injector fuel rail, almost immediately got DTCs for misfires Cyl 1 and Cyl 6 and rough running -- have done this before (many times in 300k miles) without this DTC. After this, I ran the throttle body cleaner (hook sprayer on TB from a hanging canister using shop air). If this was a crank position sensor, I would not expect Cyl 1 and 6 that are on the same coil of the 3 coil pack rail. Because MV-4 changes the combustion parameters of the air-fuel charge, a "weak" spark could cause this. Misfire vanished when engine was returned to running configuration (fuel pump feeding injector rail). After carbon cleaning and no obvious misfie, I did a vacuum gauge check on the engine (did not pull plugs to do a shop air leakdown test) -- 18 in at idle, 22 in at higher rpm. Engine does not use oil (Amsoil Signature 10-30, will switch to 0-40 at some point). Found one of the rubber 90 degree elbows, 5/16 in, that connects to the rigid nylon tubes, had a crack -- used weatherstrip adhesive and 3M 88 vinyl tape as temporary fix because the 5/16 in rubber right angle does not seem available (do you know a source? the part is not listed in the Jeep parts catalog (Factory Mopar) -- closest I could find is 53013 632AD that is "everything", not just the elbow). Just road tested. Dash tach shows no wobble at idle in park (scanner does, but only about +/- 10 RPM), and both dash tach and scanner are steady at stop lights (idle in drive). Transfer case is in AWD (not 4LO) postion. Reset MIL; MIL is staying off. *BUT*, the problem is still present -- no DTCs and no MIL. I was watching the scanner traces, my wife was driving at freeway speeds. After engine was warm (based on dash gauge), uphill, off throttle down hill (all freeway speeds 55 MPH or higher), no problem. Suddenly, engine bucked, advance went to 0. Problem went away, and no further systems. No MIL (progress) but still the same ghost. Please see the attached PDF of the traces; I have added a green arrow for the 0 degrees advance. Note that after bucking, that did not show up in the RPMs (but the sample rate may be too low/slow) the 0 degree persisted -- unless again this is a false reading from the scanner application/tool or from a PCM/ECM that did not update. Could this be a PCM or ECM problem? Usually, crank or cam sensor issues have real starting or much less intermittent driveablility issues. There also is a thread that the oil pump drive camshaft synch assembly gets "sticky" (please see image of component) on the 4l without a DTC -- could this be the cause? Do I simply "shotgun"? At any rate, after your next reply, I will file the review.. If the problem does go away after some other part is replaced, may I contact you so that you can add the "fix" to your knowledge base? One more question: assuming proper maintenance (Amsoil AF+4 trans fluid, filter changes, band adjustments, also Amsoil for the transfer case. fluid changes at service manual intervals), no jack rabbit starts, no heavy load pulls, no significant off roading, but routine use, how long does the 42RE last? How long does the NV247 (quad track II AWD/lo range transfer case) last (link belt stretching, friction plates) lAST? Ours has 300k miles, and I will replace (do not have special tools for either box) before on-road failure. I understand no one can predict a failure, but as a rule of thumb when I do the 200k mile service, I change components that I know from experience may not make it to 300k and for which I do not want to pay for an on the road fallure if we are outside auto club tow range (service parts such as filters, hoses, spark plugs, etc., are changed at regular service intervals). Thanks for all your advice.
Expert:  Juan Crespo replied 1 year ago.

Wow! I wish all my customers were as detailed and thorough as you are.

I was aware of TSB 09-003-03, but didn't recommend it because it only applies to engines that have had little to no maintenance. However, the fact that a misfire developed from the same coil makes me ask myself if that's the cause of the original issue or just another contributor. In other words, if that coil was failing before, why didn't the PCM set any misfire codes? And the only answer I can come up with is that the original stumbles were indeed caused by that weak coil, but either did not make the crankshaft slow down enough or long enough for the PCM to set a misfire code, or were not captured by a failing crank speed sensor, in which case the PCM would have set DTC P0320. In conclusion, running the MV4 served as the stressor that revealed a weak coil as the root cause of the stumble.

The good condition of the engine is confirmed by the high vacuum readings, so I don't see a problem there.

Regarding the cracked elbow on that emissions hose, the best cure is a small dab of black rtv Part Number - 04883971GB.

Jeep basically wrote the book on 4WD systems and when you combine that with the type of maintenance you have given it, I don't foresee any problems with the transfer case (didn't see them fail on customers' vehicles while I was working at the shop and didn't see it fail on my own vehicle even after 500K miles).

One weak point that I've noticed is the engine cooling system, especially the radiator. Those are not built with the same quality as the drive train components and can fail after 200K miles regarding of maintenance. Water pump and thermostat come next on that list of things to watch after that mileage.

This question will remain open for another week or so even after you rate my answer.

Best Regards.

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