Engine cuts out at random or "blips", randomly stalls at the idle, randomly stalls when you put your foot on the brake. There is no pattern and the condition cannot be deliberately reproduced. There are no error codes, but the "check engine" light occasionally comes on for a split second after the cutout, but rarely. The. Cutouts seem to be more likely when it is hot and humid, but happens under all conditions and engine temperatures.

The whole vehicle has been overhauled and virtually all componentssensors, etc are new or check out within specs. It is not any of the usual suspects.

When the engine runs, it runs perfect. Oddly enough, it only cuts out when my wife drives the car. I can drive the car for weeks and nothing happens.

Sny thoughts?

 

This very much sounds like a power loss condition. I once had a Jeep Cherokee that had the identical symptoms. We discovered that the battery hold down was not properly secured and the positive post would occasionally ground to the body causing a power loss. That's probably not what you have but I would check power and grounds first.

Second, the stalling when hot also points toward a vacuum leak. When the engine is cold and more fuel is demanded, the vacuum leak is not as consequential to the smooth running of the engine since the car is running much richer anyway. As the engine warms up and the fuel ratio becomes leaner, it becomes much more sensitive to a vacuum leak.

 

Hard to diagnose such intermittent problems... Could be several things; in my Volvo experience a failing fuel pump sometimes causes this especially when hot outside. I didn't want to do it but in the end that's what it was--bit the bullet, and that's what it was.

 

fuel pump relay is another one.

CPS sensor with sketchy wire pigtail is yet another.

but really, this is all guessing.

 

first things first check your plugs/wires cap/rotor..

 

I checked everything. Everything individually checks out. After several weeks of this, I noticed that there actually is a pattern:

First, if the engine stalls and will not restart, if you piddle around with the lead and connector for the CPS, it will restart. Apparently, the mechanics thought it would be a good idea to bend the CPS lead at a right angle right at the connector to the wiring harness. If you straighten it out, the problem goes away. After a couple of days, when the problem starts up again, I find that the right angle bend has returned to the lead at the connector. Apparently it puts enough pressure on the connector that it gets a faulty connection - That is part of the problem.

The other part is that I corrected the connection is such a way that the electrical connection in the plug would have a good contact. That works just fine until the humidity goes above exactly 60% and the engine goes into it's cut out episodes regardless of engine temperature or air temperature. Essentially, the problem becomes excessive above exactly 60% relative humidity and any air temperature.

And here is the other problem that I have noticed - when the engine stumbles, about 50% of the time the "Check Engine" light comes on for about one second and then goes out. If the engine stalls completely at any speed, the dash lights do not come one but all other electrical items keep working just fine. If I check for error codes, there are no stored error codes.

 

Sounds like a broken wire in the harness right at the connection. I believe that if you check with the Volvo dealer, those are still available as a repair item. Put a new connection on the harness.

I'd also replace the crank position sensor since I was there.

 

Something to think about. Through my 40+ years doing this, there is a recurring theme: humidity and condensation. Water collects inside electrical components and bad things happen.

The symptom is always the same: a tiny drop of water will short out a component for a second or two. The voltage burns off the water and it starts working again, until water droplets collect and short out the circuit again. Usually you get strange sudden jerks as the engine stops running, then starts right back up again.

It's often overlooked that you simply have condensation inside the distributor cap, which will cause this problem as well. Good luck.

 

Here's the scoop:

I also discovered that there are now two error codes recorded in the diagnostic system despite the check engine light not being on (the light comes on briefly when the cut outs occur) - the engine stalls at idle speed, usually as you come to a stop and push the clutch in (car will restart easily and normally 99% of the time) and occasionally it will blip at speed randomly. This always occurs at high humidity regardless of temperature.

The two error codes are:

2-3-2 - Lambda control - too lean or too rich at idle.
2-1-4 - RPM sensor signal intermittently missing.

The 232 is probably caused by the CPS either failing or the signal being interrupted (no spark signal and unburned fuel trips the O2 sensor into thinking the mixture is too rich). So, if the vehicle doesn't want to start, all you have to do is jiggle the connection and the problem goes away, for a while.

The CPS is only about two years old, and I thought that it should not fail after two years, so I checked the cable for any abrasions and discovered something interesting - it appears that someone had squeezed the cable right near the plug with what I would assume was a pair of pliers (the lead wire was flatted and you could see serrations pressed into the wire just at the connector (idiot mechanic probably used pliers to pull the lead into position).

The mechanic who replaced the CPS two years ago claimed the old CPS failed because it was grounding out where the connection passed through the firewall due to the absence of a grommet. This is absurd because the wire for the CPS goes into a bundle of wires and then through the firewall - and the stock grommet is in tact.

So, would it be safe to assume that there has been some kind of failure involving the CPS lead or connector? It worked fine for two years and then suddenly this problem arose.

 

Replace the CPS. From what you describe that is most likely the cause of your stalling.

 

Bingo! Problem solved. It was the CPS. A new OEM CPS cost me a whopping $40 and took a total of about five minutes to replace from the top end. It wasn't easy - the design engineers thought long and hard to make it as difficult as possible to replace.

The old CPS (put in by an idiot mechanic who took literally two months to do it, all they way claiming it was a bad Jetronic unit, which, of course it was not) used a used part. To make things worse, it looks like the guy grabbed the cable in several places with a pair of pliers and crushed the cable near the connections at both ends. It was a miracle that it even worked at all.

But I'll tell you why this part is so prone to failure - the heat gets to it. It is mostly plastic and the old one was fairly cooked.

 

The CPS usually last 10-15 yrs... You can route them farther away from engine along the firewall... Some techs just let them float around too close to the engine, easier for heat to get to them like that.

 

I must agree with above. There is a lot of motion on that engine and the CPS dangles back there between the top electrical connection and where it is bolted to the block. It rubs along and eventually the foil shielding wears away and you lose a signal.

For what they cost, replace them when they fail. Before I figured out what was a problem, I spent many hours years ago trying to diagnose a no start condition on a Volvo 4 cyl. When I learned about the crank position sensor and fuel pump relay, I went into high gear diagnostics. LOL

 

Three spares I carry in the trunk are , CPS , radio suppression relay and fuel pump relay.

 

Funny you should mention the shielding - I dissected the old CPS and looked at what happened - the culprit was vibration and the fact that the mechanic who installed it went out of his way to crush the cable at the connector and just at the sensor itself - (this was the same mechanic who got pissed when I told him - after the car being at his shop for two months -, "if you can't fix it, I'll just load it up on a flatbed and take it to Volvo." - he had it fixed the very next day).

But what it is, is that the cable for the sensor is a shielded cable like you use in RF applications like cable TV. This means that there is a specific impedance to the cable which is altered if the shielding is crushed or violated. If the impedance is off, it will pick up RF burst from a spark plug which puts a notch in the signal going to the ignition module causing the Jetronic unit to misinterpret the RPM data. this in turn will suddenly cause the Jetronic unit to either make the mixture very rich or very lean, which causes a loss of power for a brief instance, and sometimes a total stall.

Virtually every signal from every sensor and every spark/fuel related component goes through the Jetronic unit, which, of course, means you can check every component in the system by simply pulling the bus connection off the Jetronic unit and (if you know the proper pins to connect to) check the resistance of every component in the system. If you are really nit-picky, you can hook up an oscilliscope to any given circuit and test it across a range of voltages or even send false signals to the Jetronic to see how it behaves. But that's if you have too much time on your hands.

The Jetronic units are fairly simple affairs in terms of how they work and how you can fix or 'rebuild' them - most of the parts down to the tiny memory chip are fairly common parts that you used to be able to pick up at a Radio Shack store, or pirate from other electronic equipment.

The funny thing about these Jetronic EFI units and Ignition Modules is that they are nearly identical to (with the exception of the memory chips and circuitry designed to create and record error codes) the electrical fuel injection modules used in the WWI German ME BF 109 aircraft (purely 1930's technology without the vacuum tubes ), but much more simple in design and function.

 

huh, didn't realize the germans had invented 8 bit embedded microprocessors in WW-I.

the LH2.2 ECU is based on an i8048 processor, while the LH2.4 is a i8051 family CPU. all timing and everything is done with digital loops.

the injection in the Mercedes DB601 engines used on most wartime Bf109's was mechanical direct injection, with a piston fuel pump below each cylinder, mechanically timed. early planes used a Juno engine with carburetors