Intermittant cold running issue: 4000 RPM wall

[740Weapon]

Hi,

My B234F has a very confusing itermittant cold weather issue.

Last year, in the extreme cold of maine in a snow storm my car had a strange issue where it could barely get past idle without coughing and fluttering like it was running out of fuel or something. During this entire issue the main fuel pump was humming good and strong. I replaced the fuel pressure regulator despite the fuel pressure being fine and the issue didn't happen again. Later i checked that the in-tank pump was working.

Later that year, the catalytic converter broke apart and clogged up the exhaust. When it failed the car could not rev past 4000 rpm, even in neutral. I then replaced the entire exhaust and the cat.

This year. I was driving to work on a very cold moring and i pulled onto the highway, hit 6000 rpm in second gear and the car was running strong. Later i tried to pass someone and the engine hit a wall at about 4000 rpm, even in neutral.

the first time it sounded like detonation or fuel starvation, but any time after that it sounded like the clogged cat did.

That same afternoon the car ran strong again.

Today i dropped and inspected the catalytic converter (which is not fun) and it is FINE!!!

So, what the hell could be causing my cold-weather specific intermittant power problem.

I just want to have christmas and go skiing damit!

Thank you much,
-Dana

edit: the car could hit 6000 rpm in neutral under light throttle, but under load it couldn't break 4000 rpm.

 

[Kjets On a Plane]

Try another AMM? Mine was notably bad cold before it finally went all together. Intermittant power pulsation, odd lean and rich behavior for no reason, no power/good power in and out. What color is the label on the ECU of this 1990 vintage beast?

Codes in the OBD? What is the 02 sensor doing when all this drama is going on?

Does the car take a while to crank sometimes? Crank angle sensor been done already?

Even with a good AMM and no airbox thermostat, sometimes LH cars take a sec to quite get their bearings before they run right when it is real cold out (like 0-10F or so cold or colder). It doesn't bug me, since I can live without that stupid thing, but I do notice a little when it is real cold out.

 

[740Weapon]

Thank you much for the reply.

the AMM has not been looked into seriously. I will be sure to disconnect the AMM next time and see if the car goes into regular olde limp mode. Next time i am at the JY i will grab another B234 amm.

idk what color the ecu is. what label color is bad?

This car has never had an OBD code unfortunately. 1-1-1 is all it ever tells me.

The VR sensor is within 2 years new.

 

[Kjets On a Plane]

B234 should use just a generic 016 LH2.4 4cyl amm. Its used ona ton of volvos, the odd saab and god knows what else. You should be able to pirate one off one of your other LH2.4 cars to diagnose this one. Air mass oily or nasty looking on this one at all?

Same story with the 02 sensor on N/A cars....turbo cars have a shorter 02 wiring loom.

Crank angle sensor is probably fine if the wiring hasn't rubbed through, though most 16Vs leak a crap ton of oil out of the head, so it might be rather oil soaked.

How's the dist cap/wires etc look on it? Spark blowing out? Wires oil soaked and separating in the head (they leak a lot in the spark plug holes usually)? You should be able to steal a known good cap and rotor from a 700 8V. Dist cap real oily from bad seals in the dist (there are 3 to update on that miserable dist)? Pity 16V cars can't use a 240 dist...the 740 dist is criminal...not as bad as some benzes and PRVs got, but waay too expensive and annoying. Wires are pretty 16V specific, sadly.

White label ECUs are the ones that are less likely to kill the fuel pump relay circuit, then crank angle circuit or 02 sensor circuit of the early 89-early91/late 90 LH2.4 cars. Earlier LH2.4 cars use pink label (worst) and green label ECUs usually. 1990 turbo cars don't seem as afflicted as the 89-90 LH2.4 N/A 240/740 cars. If the car runs ok most of the time and 02 sensor oscillates, usually it's completely fine.

Coolant temp sensor resistance in spec? Usually if it isn't the car sucks to start or runs like crap cold, and if it is real bad you definitely get a code and horrible fuel econ.

Electrical/engine tune crap like this I just do the critical resistance tests in the bentley (amm, coolant temp, crank angle sensor, OBD (probe at the ECU connector and at the sensors if possible) and start swapping out known good stuff from another car that runs fine to diagnose it quick. The beauty of LH/EZK is that for the most part, individual stuff either works or it doesn't.

Shot in the dark of unlikely: Ignition powerstage once in a while. Rare on 90 and newer LH2.4 cars, and usually the car stumbles or has other running issues before dying hot, but it never hurts to eliminate all the variables.

 

[Gabe244]

I had this problem yesterday with my car (nothing to do with temperature im afraid). It would idle (barely) but when you floored it, it wouldnt go past 2k. It would hit it, the pod filter would grunt, and then stay there. As it turned out, the ignition timing was Waaaaaay retarded, and it was all fine and dandy once i advanced it.

The moral of the story is, check your timing!

 

[740Weapon]

update on this issue:

very cold 2.5 hour drive from mass to maine. Issue happened many times. Happened with 2 different AMMs, Happened with O2 sensor disconnected, happened with AMM unplugged. the 'wall' happened at different RPMs on different occasions.

but this is where it gets weird... If i turn off the car for more than about 5 seconds the issue goes away and the car runs fine for an unpredictable period of time between 2 minutes and 45 minutes, then all a sudden the motor basically loses the will to run above (fill in the blank) rpm. So this leads me to believe that the issue is with something that has a brain... I have trouble believing its the ECU or EZK or any relay in the fuse pannel because the car had the heat on high for the entire 2.5 hour trip...

So any further advice? or at the very least can someone list off components with digital circuitry that would be consistantly exposed to the cold? Powerstage?

my next investigation will be to have someone smell the exhaust while i rev it to the wall in neutral... or get a noid light and see if the injectors do something funny when i hit the wall...

DAMN YOU WINTER!!!!

Ohh, and thanks for taking the time to write out such detailed advice 945ti.

 

[JaxMKII]

sounds like Mass air flow meter giving bad data.

 

[Kjets On a Plane]

Freaky. I follow your logic of "whatever does it probably has a brain" since it works ok for a while after you reset it and changing the airmass, powerstage and other stuff doesn't change it. Do swap the power stage if you haven't.

Try a later model 16V ECU? Or toss a turbo ECU (easier to find) and some 850 injectors in it?

 

[740Weapon]

Freaky. I follow your logic of "whatever does it probably has a brain" since it works ok for a while after you reset it and changing the airmass, powerstage and other stuff doesn't change it. Do swap the power stage if you haven't.

Try a later model 16V ECU? Or toss a turbo ECU (easier to find) and some 850 injectors in it?

thanks for the input.

I am trying to grab a 16V ecu, icu, powerstage, some relays, and other 'brain' items from a 16 valve part out in the for sale section... hopefully that transaction goes smoothly and I can get some more data points within a few weeks.

 

[Kjets On a Plane]

How much will you be killed if you steal injectors and ECU out of a certain 92 244 N/A with LH2.4 for testing? It should tell you what you need to know. For that matter, it will run a bit richish if you leave the 16V injectors in but use the 8V fuel computer, but it should run more or less ok and tell you if your strange 4K wall is a fuel brain thing.

Power stage, AMM, and relays should be the same as any other LH2.4 and newer 7-series (except the regina cars of course).

 

[740Weapon]

It would not suprize me if the problem came back, but this is what happened so far:

I did the cap/rotors/plugs/wires and rebuilt the dizzy because it was leaking significantly.

the cap had significant wear... AND like a clown i had my MSD coil wired backwards.

once i fixed all of these parts the problem basically went away (happened once in several weeks).

I then replaced the powerstage and the problem hasn't happened yet.

So i hope the backwards coil and worn ignition system abused the powerstage to death and I'm keeping my fingers crossed the issue doesn't return.

 

[boostin'xr4]

update on this issue:

very cold 2.5 hour drive from mass to maine. Issue happened many times. Happened with 2 different AMMs, Happened with O2 sensor disconnected, happened with AMM unplugged. the 'wall' happened at different RPMs on different occasions.

but this is where it gets weird... If i turn off the car for more than about 5 seconds the issue goes away and the car runs fine for an unpredictable period of time between 2 minutes and 45 minutes, then all a sudden the motor basically loses the will to run above (fill in the blank) rpm. So this leads me to believe that the issue is with something that has a brain... I have trouble believing its the ECU or EZK or any relay in the fuse pannel because the car had the heat on high for the entire 2.5 hour trip...

So any further advice? or at the very least can someone list off components with digital circuitry that would be consistantly exposed to the cold? Powerstage?

my next investigation will be to have someone smell the exhaust while i rev it to the wall in neutral... or get a noid light and see if the injectors do something funny when i hit the wall...

DAMN YOU WINTER!!!!

Ohh, and thanks for taking the time to write out such detailed advice 945ti.

That's happening to a local car here. It's a +t'd '87 240 with Lh2.2 and the Chrysler box. It did the problem both before and after the +t. We've swapped ECU's+ICU's separately, AMM's, ECT's, knock sensors, 02 sensors, everything.

It hits a different RPM every time, and changes tone. Sometimes it's a hollow, howling tone, and other times it's agressive and misses a lot.
Sometimes it's smooth and it sounds like we're holding the throttle steady.
The only thing that's common between all these problems, is a 'key cycle' temporarily solves the problem.
I've become so familiar with the problem, that from the second we start the car I know whether it will do it or not.