[raymondo112]

Na the ECM is the last place you should ever look, 9 times out of 10 the ecm is never the problem, if it ever happens to be, all kinds of funny things will happen and you will probably have multiple codes, at that point of a complete no start situation period which is very rare unless you drive the car in some deep water and the ecm gets submerged that might do some damage.

Also the 3.3 and the 3.5 have the potential to last forever but the 3.5 requires more maitnance to do so mileage is never an issue unless no maitnance has ever been done.

Sounds like you may have a leak in vacuum from your description, but I can't honestly tell, when you start the car how does it run at idle is it shaky or feel like a misfire may be there steering wheel shake a little, when you add throttle does the problem smooth itself out and seem to disapear, if so that is a classic symptom or a vacuum leak or sometimes on these 3.5's an intake gasket leak, it may not be too bad yet, but will get worse if it is one of those.

Also not a bad idea to check your spark plugs, if you are not running champions in this engine then you will be suprised how bad it will act up when you put some miles on any other brand of plug, I have brought many 3.5 engines back to life and curred all kinds of weird idling and acceleration by installing the recomended champion copper plugs, I suggest copper as you get the best spark out of copper, platinums suck unless you have a hard time getting at the plugs and rather change them less often, but the spark isn't as good and they run a few bucks more, not worth it in my opinion.

Also I recomend 89 octane as these engines were made for it and should be ran off of it all the time, I did the math when I owned mine and I was only paying 1.90 extra per tank and got better performance and gas mileage from it than the 87. So all in all I was spending more on the 87 in reality due to the drop in fuel economy.

Well report back and let me know what you find....

 

[ImperialCrown]

Agree. In any service manual diagnostic procedure the PCM is the LAST item to be considered as the culprit, never the first.
To help take the guess-work out of this, we need a data recording to find what is dropping out when the 'blip' occurs. It may be a momentary sensor supply voltage loss and could be wiring harness/connector related. If you can get it to blip consistently, that increases the chances of finding it.
Many OBDII scan tools offer a data recording function. Look at the 5 volt sensor supply and the various sensor outputs. See if any drop out when the blip occurs.
This could be secondary ignition-related. An intermittent misfire may not set a code. A thin black streak on the spark plug porcelain insulation may indicate an arc mark. How are the plugs and wires and connecting coil towers? A smear of dielectric silicone grease on both ends of the wire boots helps prevent arcing and aids removal when necessary. Once an arc trail is made it usually can't be simply cleaned off and only the replacement of the affected components will prevent it from coming back.

 

[Opus62]

Thanx for the replies.

The engine runs smooth as silk in all conditions, hot or cold, wet or dry. The effect seems independent of any outside stimulus that I can discern. I always run 89 or higher octane, depending on what's available. There is no pop or backfire. It uses absolutely NO oil between oil changes. I am now running 5W30 Castrol Syntec. I wish there was a pattern of some sort, so I could try to duplicate the issue.
The "blip" is very brief, a mere fraction of a second but from how it feels, it seems that all 6 cylinder shut off for a couple of revolutions. Hard to tell, of course, but it seems that way. Could only be one cylinder for all I know :frusty: . Still no codes stored. It is a 1994 so it's not OBD2....is it? :working:

 

[ImperialCrown]

It is OBD1. Most newer OBD2 scan tools won't work.
A DRB3 (or equivalent) with the LH body cable would be the tool to interrogate the PCM with. The DRB2 scan tool stopped supporting vehicles after 1993.
I think that the Chrysler Co-pilot data recorder is only for OBD2 (1996-up), but you should ask a dealer. If the Co-pilot doesn't do OBD1, you would want to use a live scan tool on a road test with a helper (technician) with you to watch what happens to the PCM sensors/inputs/outputs when the blip occurs.
I think that an OBD1 scan tool/data recorder may be the only way to diagnose this and you don't want to just start replacing parts. You might want to start out by checking and cleaning all ignition and EFI-related electrical connectors first.

 

[Opus62]

New development. The car has now started stalling at idle. Rather hot day today at 28 degrees. I was in a Tim Hortons drive thru with the A/C at MAX when the engine decided to stall. This was after about 8 minutes or so. It started up after that with no difficulty at all. 10 seconds later stalled again. Restarted with no difficulty. Remained idling good then I finished in the drive thru. Drove home with no difficulties, even after stopping at a red light. Drove home in about 5 minutes then parked the car. Shut off the A/C and the stereo. Decided to let it idle for a bit to see what would happen. After about 30-40 seconds of idling, it stalled. This might be positive, as it seems that I am now able to duplicate the issue, which will be very valuable with diagnostics. Before all this started, I have driven home 25 minutes from work today. On the way, it did the "blip" once. At no point thru all this has the car ever been un-drivable. It has very good power on demand, passing on the highway with relative ease.
About the only commonality with all this is that the engine is at operating temperature. Oh.....and no codes stored. :frusty:

 

[ImperialCrown]

There was a fuel injector o-ring and possible fuel rail replacement recall on 94-97 3.5L LH cars that could cause stalling and rough idle, etc.
I have had to re-perform some of these recalls years later because the problem came back or the plastic fuel rail that wasn't leaking before, was now.
You may or not sell gas, but usually the right bank would run richer than the left bank. This would give adaptive fuel trim values in the negative numbers on the right bank and normal on the left bank.

 

[Opus62]

Interesting morning yesterday. After dropping off my daughter 20 minutes into my commute, the car did the blip again but was much different. It did several in rapid succession then stalled, while driving at 30 kmh. I found this rather disturbing but the surprising thing was the "cruise" light on the instrument panel was flickering along with the engine blips. The cruise control was not turned on since I only use cruise control on the highway. I pulled over, anticipating a problem. When to start the car, it started right up and ran fine. I finished my morning commute, engine blipped a couple more times on the way. On the way home from work I was travelling at 100 kmh when the blip happened again. Fortunately, I happened to glance down to the IP at that moment. At that moment, the tachometer needle had quickly dropped almost to 0 then jumped back up to normal. It seems that, for the duration of the blip, the tach does not receive a proper signal. Yet again, no codes stored. :glare:

 

[68RT]

Not the expert on this but I am thinking Hall effect. Can someone with more experience on this respond?

 

[valiant67]

No hall effect on this. Instead it uses a crank position sensor and a lack of signal from the crank sensor would interrupt spark and send the tach to 0. And the crank sensor may not set a code when intermittent.

 

[Opus62]

Most interesting. A crank position sensor is quite cheap and readily available. Might be worth the effort to pop one in.

 

[Opus62]

I'm back!!!

After a vacation and heavy work load [busy season, RV business] I can now pay more attention here. AND...there is a new development now. The aforementioned power blip became more frequent, with "no start" situations happening a few times. New codes now. Code 11 started to appear, confirming [I believe] the crankshaft position sensor issue. All came to a head yesterday on my way home. Engine stopped completely.No start, period! Codes now are 11 and 54. So I decided to replace both the cam and crank sensors. Today, the code 11 is now gone BUT engine still will not start. Code 54 remains, even after replacing the cam sensor. A direct check reveals no spark. However, when I crank it over, it will "kick back" once, as if I had a distributor too far advanced. [oh the memories ] A following attempt at cranking will appear normal.
I know it must be something simple, but what? :frusty:

I just thought of something....timing belt????

 

[chuzz]

Try putting your old cam sensor back in and see if it will start. I'm no mechanic, but it seems to me you replaced it without needing to. Where did you get your sensors? If they're aftermarket and not Mopar, that could be the problem.

 

[valiant67]

I don't think the cam sensor would stop the spark. I think that is controlled entirely by the crank sensor.
Timing belt would be a good thing to check, but if it seems OK I guess next would be verifying power is getting to the crank and cam sensors.

 

[seajai]

Had and intermittent stall with a no start for 5-10 minutes on my car a while back. It would also buck when trying to restart and did not set any codes. I replaced the crank sensor with a Mopar one and havent had any issues since. I've read in multiple forums that aftermarket sensors are prone to failures and OEM is the only way to go. If you are getting a "kick back" while cranking, it must be getting some spark, just not at the right time.

 

[Opus62]

I tried to put the old cam sensor back in. No difference. Still code 54 but no code 11 anymore. I tried checking for spark with a spark tester. No spark at all and I know from experience that these ignition systems have a wicked hot spark. I have been told by [unconfirmed] sources that, if the cam and crank signals are not in proper synch, there will be no spark at all. Don't know for sure on that one but it seems possible. The crank sensor will tell the ECU how close to TDC a piston is but the cam sensor tells the computer precisely which 2 pistons are on their way up. Much aggravation. Off to work now.

 

[Opus62]

Update! Upon returning home from work, I decided to check for the possibility of a timing belt issue. Took out the cam sensor so I could look down the hole while turning the crank pulley. Could turn the pulley all I wanted but no movement from the cam. And there ya have it, I have a confirmed timing belt problem.
Now, I have read some comments that it is possible, with some "persuasion", to install the new belt on the crankshaft without removing the crankshaft pulley/balancer. Has anybody ever done this without a puller?

 

[FIREM]

Good news is the "early" 3.5's like yours are "non interference" meaning you should be OK to replace the belt. (later years will bend valves). While it can be done without removing the damper it is not recommended. You would have to twist and shove the new belt past the damper ant that stresses the new belt. Most auto parts stores will "loan" or rent a puller. Reinstallation either get a longer bolt to pull the damper on or I warm the hub with a small torch, start it on the crank and gently tap it on enough to start the bolt to pull it on. Good luck.

 

[Opus62]

Mission accomplished. Belt was very easy to slip past the damper. No real "twisting" to speak of. Also replaced the crankshaft position sensor. Car now runs well with no power lips. I also replaced the water pump and the tensioner. The original tensioner was plastic, replacement was metal. Lining up the timing marks was a real bear to do. I can't count how many times I found myself out by one or two teeth after each test rotation. That was the longest part of the whole reassembly process. All is well, so far. :3rd:

 

[chuzz]

Congratulations on the repair. Happy motoring.