I need some help. I am working on restoring a '94 Town & Country van. I bought it with a blown engine, but a great body and interior. Installed a donor 3.8 VIN L engine out of a '94 T&C from the local Wrench n' Go. The engine cuts-out under load, but most of the time if driven gently, the van can be driven without missing a beat. The PCM has set no codes. Cycling the key returns only codes 12 and 55. The van has 147K miles, the "new" engine about the same. Here is what I have done so far to try to fix or identify the problem:

Purchased an AllDataDiy subscription for the van mostly to get the wiring diagrams
Tested fuel pressure - 40 psi running with light throttle - 48 psi with heavy throttle
Pulled and examined 8 ounces of fuel from rail - clear with no evidence of particulates
Installed new NGK copper core plugs
Installed new plug wires
Swapped known good coil from my '98 3.8 Caravan - no change
Installed new crank sensor w/ .030" paper spacer - no change
Installed new battery
Disconnected vacuum to EGR - plugged ends - no change
Renewed battery cable terminal ends, cleaned, tightened battery cable grounds.
Verified function of ASD relay
Checked/redid all engine and chassis grounds in engine bay and under dash
Isolated and confirmed that wires to and from the PCM can carry brake-light current while being wiggled in the following circuits: Coil, CkPS, CPS, ASD relay, TPS, CTS, B+, Ignition voltage, and all related grounds.
Checked for corrosion or pin damage at all engine compartment connectors and headlight switch.

Made some tests by splicing an LED test lamp into various circuits and found:
12V to coil from PCM (pin #57 DG/OR) Lamp flickers when engine cuts out, goes out when engine stalls.
Ground to ASD relay from PCM (pin #51 DB/YL) Lamp flickers when engine cuts out, goes out when engine stalls.
Battery feed to PCM (pin #3 RD/WH) Lamp stays bright at all times. Does not flicker when engine cuts out.
Ignition feed to PCM (pin #9 DB/WH) Lamp stays bright in run and start - does not flicker when engine cuts out.

I do not understand how the PCM functions well enough to know for sure, but assume (?) that the miss is caused when the PCM cuts the ground to the ASD relay shutting down the coils and injectors. When running down the road while accelerating or otherwise under load, this is felt as a hard miss or jerk, when it occurs during idle, it usually stalls the engine. It readily re-starts. I would consider a bad PCM, but it seems that it is maybe doing what it is supposed to do.

I have read that a bad crank or cam signal can cause a miss, stall, or no-start condition in pre-96 Mopar ignitions. I am wondering if the crank signal is momentarily lost under load due to a damaged flex plate or the cam/crank sync is lost due to a worn timing chain. I don't mind changing the timing set, as with 150K, it is time anyway, but I would hate to drop the trans if the flex plate is not the problem.

Am I understanding the PCM correctly? Have I overlooked something simpler?

Thanks for taking time to read.

Edit: The problem was the PCM. The original PCM in the van had been replaced with one for a 3.3 engine. A junkyard PCM from a '94 T&C with a 3.8 seems to have resolved the problem.

 

Hi Bill
If i had a van with a problem like this, i would have a co-pilot on the van and drive. This way when the van acts up, this will help to find the problem. So if you have access to a co-pilot, i would hook one up and have a dodge tech down load it to the MDS( work computer) for the dealer.

 

Thanks, Master Tech, for the reply. Unfortunately, I have no access to a co-pilot. It would be great if there were a store that rented them to folks. I see on-line that the cost for purchasing the tool is greater than the value of the van. As little as I would use it, I could never justify the cost. The closest dealer is now about 15 miles away and will want $100 or so just to hook up a DRB tool. Don't even know if they have a co-pilot, but it won't hurt to give them a call to see.

I do have an older Actron 9110 scan tool that works great for pre-OBDII GM and Ford products. It does a pretty good job of data logging. The problem is, I do not have a Chrysler cartridge and cable for it. I have been looking on E-Bay for those, but have not seen any offered since I have recently had the need for it.

 

How is the fuel flow or volumn? How old is the fuel filter? You might also want to check the cam sensor.

 

Thanks for the reply, Tizzy.

I can't speak to the fuel volume except to say that I tested the fuel pressure at the rail and got 40 psi idling and about 50 psi when I quickly "blipped" the throttle. I removed the hood from the car and wired the gauge up on a stick so I could monitor the fuel pressure as I drove and the engine cut out. At 60mph, the fuel pressure was about 40 psi, and when accelerating rose to about 48 psi. The engine tends to cut-out under load, so the "miss" occurred with a fuel pressure of nearly 50 psi. I figured that even though the pressure is somewhat lower than specification, it held steady during the cut-out events. I also bled off about a half-pint of fuel through the relief valve on my fuel pressure tester into a mason jar. The fuel is clear with no indication of dirt or water.

Those results and the test light that showed power to the coil and injectors cutting out when the engine cut out lead me to believe that the problem was ignition rather than fuel. I bought a new cam position sensor and I guess I will install it, but I am not holding out much hope that will fix it as there are no codes set for cam sensor. I have heard that the crank sensor can fail without setting a code, but had not heard that for the cam sensor. (?) Given that the ignition and battery voltage to the PCM remain constant while the ground to the ASD relay is interrupted during the cut-outs, I was wondering if anything besides the cam and crank circuit would normally cause the PCM to open the ASD.

I should have also mentioned that when the engine cuts out, the digital speedometer reflects it by displaying for a fraction of a second some value that is much less than actual. For example, if the engine cuts out at 60 mph, the speedometer might briefly display 17. One other thing, I just recalled. When I pulled the old crank sensor, there were metal splinters clinging to the end of it. I did not think much about it at the time, but am now wondering if that could be evidence of damage to the flex plate. The pieces were larger than filings or dust that you might expect from starter gear or ring gear wear.

 

The ASD only actuates if it sees a input from the cam and crank. So if you lose either one, the ASD shuts off. Alot of cars we build, they just use the crank sensor for starting, it could crap out after that and run fine. The cam sensor is the most important of the 2.

 

And your probably right, more than likely it will be a harness issue.

 

Well, tomorrow I will install the new cam sensor and see what happens. Perhaps the intermittent nature of the fault somehow prevents the PCM from setting a code. I wish I knew more about how the PCM works.

 

Ya, me too

 

Installed the new cam position sensor. Boy, that old one was hard to remove! Did not make any difference. Then, before opening the front of the engine or dropping the trans, I wanted to make double sure I did not have a bad ground to the PCM. So, I spliced my LED test light between the following PCM ground wires and the positive battery post: PCM pin 4 BK/BL signal ref; PCM pin 5 BK/WT signal ground; and PCM pin 11 BK/TN power ground. The test light for all three stayed steadily lit while the engine cut out.

My conclusion at this point is that I either have a bad PCM or there is something causing loss of synchronization between the cam and crank signal to the PCM causing it to momentarily open the ground connection to the ASD. The only things I can imagine that would cause that are a cracked flex plate or a sloppy timing chain. There is another option- I could buy the Chrysler cartridge and cable for my Actron scan tool which would allow me to look and record cam crank synchronization when the engine is acting up. Cost is about $110 and I would have to wait a week to get it shipped.