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240 Diagnosing intermittent rhythmic power cut

Lando

Lando

Arthur Digby Sellers
Joined
Mar 3, 2011
Location
SLC
1986 245, B230F, LH2.2, AW70

My 240 has developed an intermittent driveability issue. The power will cut out and cut back in about once a second if I go over 3000 rpm or if there is a decent load on the engine (steep on ramp is enough to trigger it). Sometimes (when ever I'm trying to diagnose it) the problem will go away. The car has no problems idling but when the issue is occurring it will nearly die and the rpms will drop to a few hundred if I have the throttle depressed. Also, restarting the car will generally take care of the problem for a while until it comes back. I don't even know where to start really. Anyone have a similar problem?

Based on how quickly the engine cuts in and out I suspect an ignition problem. Any ideas are appreciated.
 
Checked the cap and rotor? Last time I replaced mine, just as a "while I'm here figuring out what's really wrong" procedure, it was the magic. Couldn't believe it, they really didn't look bad...
 
I went through something very similar and I also thought it was ignition related cause it only happened under load. Ended up being the fuel pump was dying.
 
Just had another bout of this except for this time it stalled completely and would restart but stall within a second or two consistently. I coasted into a parking lot and let it sit for a minute and it restarted but still had issues but didn't completely stall. I got it home and swapped out the ECU with a known good 544 unit and no change. I would have swapped out the ICU first but I don't have one on hand. Then before I could trouble shoot anything else, it started running normal again. Also, I recently replaced the cap, rotor, plugs, wires and O2 sensor. While it was acting up, I unplugged the AMM to go into limp mode and it still stalled immediately after start up. The suddenness of the stalling still indicates an ignition problem to me. I'm looking at buying a new ICU and distributor and putting them in my glove box so I can trouble shoot the next time this happens. If it was a constant issue, I would have had it solved by now because these systems are stupid easy to trouble shoot. Unfortunately this intermittent issue goes away as soon as I get out the DVOM and green book.

Also, this seems to be somewhat heat related. It has never occurred below 80F and usually after at least 15-20 minutes of driving. Letting the car sit for a minute before restarting usually solves the issue.
 
Just got it to replicate the problem. Hall sensor checks out, coil checks out. Now it's working again.
 
Don't know how 2.2 reacts but on my 2.4lh b230 the knock sensor was bad. Apart from rough running, hunting idle, it was cutting out at any load more than going 50-60mph and sometimes random. Fuel consumption was higher than usual, engine ran slightly hot.

Easy enough to check, resistance should be infinite on a static sensor (sensor will pick up charge and hold it when you mount it and stuff, it's a piezo thing after all)
 
JW240 said:
Don't know how 2.2 reacts but on my 2.4lh b230 the knock sensor was bad. Apart from rough running, hunting idle, it was cutting out at any load more than going 50-60mph and sometimes random. Fuel consumption was higher than usual, engine ran slightly hot.

Easy enough to check, resistance should be infinite on a static sensor (sensor will pick up charge and hold it when you mount it and stuff, it's a piezo thing after all)
Click to expand...

I don't know why the knock sensor never crossed my mind as a culprit, but that sounds like exactly what I was dealing with. It tests out fine now but the car also isn't acting up right now. I guess I could unplug it next time it acts up and it should start running again right?
 
Also worthy of note: the car started back firing consistently on decel. Which also points to the knock sensor (pulling timing constantly will cause backfires).
 
Never had a knock sensor fail before so I'm not exactly an expert on that subject. It's easy enough to change. Pn yyyyyy046. Disconnect will probably trigger base timing, not sure.
Mine did back fire in the intake and bent the throttle plate, causing a high idle condition. That combined with the knock sensor wasn't easy to fix, some conflicting symptoms.
 
This sounds like the coolant temp sensor symptoms to me.

Is your car auto or manual? Are you turbo or NA?
 
You describe secondary ignition failure to the letter.

You've been through the common 'Go-To' parts cannon 'try this before diving into a nightmare' things.

Grounds for everything. Find them. Clean them.
Power supply to ignition ECU. We all know how it goes with old wiring harnesses.

Fuses. Voltage needs to be same on both sides of the fuse when the circuit is loaded with the car running.

These are the joys of intermittent disasters. Naturally best time to test is when it is doing it. The E-55 did similar with an ignition coil failing multiple times. Wouldn't store a code until it got bad enough to go into limp mode. Go to test and as if by magic it would heal itsself. When I got to having replaced four coils via this method it got the other four. :roll:
 
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Lando said:
Haven't been able to get it hooked up before it quits. I just loaded my fuel pressure tester into the car, so I can test it next time it quits.
Click to expand...

I did not make myself clear.

You need to monitor fuel pressure under load. Static pressure, idle pressure, loaded pressure, pressure hold after pump is off, are the four states that need to be checked.

Hook pressure test gauge up and duct tape it to the windshield so you can monitor it while you drive.
 
JohnLane said:
You describe secondary ignition failure to the letter.

You've been through the common 'Go-To' parts cannon 'try this before diving into a nightmare' things.

Grounds for everything. Find them. Clean them.
Power supply to ignition ECU. We all know how it goes with old wiring harnesses.

Fuses. Voltage needs to be same on both sides of the fuse when the circuit is loaded with the car running.

These are the joys of intermittent disasters. Naturally best time to test is when it is doing it. The E-55 did similar with an ignition coil failing multiple times. Wouldn't store a code until it got bad enough to go into limp mode. Go to test and as if by magic it would heal itsself. When I got to having replaced four coils via this method it got the other four. :roll:
Click to expand...

I got a gently used updated harness from Philski when I bought the car 4 years ago. Grounds were cleaned during install. Ignition coil is on the parts canon list. Hard not to fire the parts canon when I only get 5 to 30 minutes to test this every few years and t is usually when I?m on the road with hardly any tools.
 
Dirty Rick said:
I did not make myself clear.

You need to monitor fuel pressure under load. Static pressure, idle pressure, loaded pressure, pressure hold after pump is off, are the four states that need to be checked.

Hook pressure test gauge up and duct tape it to the windshield so you can monitor it while you drive.
Click to expand...

I?ll do this. My last Volvo had the Schrader valve on the fuel rail. This one doesn?t, so I need to buy a new fuel rail or insert a T into where the supply line meets the fuel rail.
 
Four years is plenty time for everything to go the way it does.

Keep in mind that 'New out of the box' parts is not the same as 'Replacd with known good parts.'

Many times I have had secondary ignition parts that were junk. Good brands too. Happens.

Ever hear any rattling in the exhaust? She seem less noisy out the tailpipe under load then in the past? I've seen exhaust kittah turn 60 degrees or more to restrict exhaust. Straightened out after decel. Everything happens in our old junk.
 
JohnLane said:
Coolant temp sensor resistance does not change with load.
Click to expand...

Good point... also... I think it got brought up in the interim but power stage or coil stuff I could get on board with. When my power stage went it sort of faded out... like I was able to get it to about 3k with full throttle (this was on a Saab... but the power stage is the same on the Volvo)
 
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