940 Rough Idle, Total Power Loss

Sudden Rough Idle, Total Power Loss

So I'm headed to town this morning with the fuel gauge reading ~1/8 and a warm engine. I take a turn and get in it a little, boost comes on hard and it spins a bit in 1st, I stay in it. About halfway through 2nd it starts breaking up, not a detonation like sound, but different. Reminds me of when the c-clip inside the distributor broke on my Mustang and the timing was all over the place.

Anyway, I get out of it and am cruising about 60. I go another quarter mile or so and it starts losing power, fast. Soon I'm down to 40 and can't do anything about it. If I added throttle it would kinda lay over, even though the boost gauge would read a few psi. I knew right away it wasn't another blown intercooler hose. I'm thinking it's out of go-go juice as the fuel gauge is known to vary a bit every time I start the car.

So I pull over and check under the hood and nothing obvious is out of place. I throw a couple gallons of 87 in it to see if I can limp to a gas station. Nothing, no change. CEL is on now and I pull codes from A6. 1-2-1, faulty AMM signal. So I unplug the AMM to put it in limp mode and no change. Call AAA, ride home in tow truck.

Now I've done some research here on the board and checked all the basics I can think of (except fuel pressure, waiting on the gauge) and have found nothing. The car will still start (quickly, usually it has to turn over 5-6 times) and kind of idle but can't be put under any kind of load. It was literally floored just trying to get into the shop and I still had to kick my leg out the door and neutral drop it a couple times from 2000 RPM just to get up the incline.

So I'm turning to the collective knowledge of the board. Any suggestions?

I should also mention that the idle has been pretty rough (more so than normal) the past couple days. Not stumbling or anything, just kind of a lope to it that wasn't there before. I wasn't too worried about it as I have a ton of tune up parts to throw at this thing once this problem is figured out.

Bad amm and/or bad fuel pump.

major vac leak?

probably the amm. replace the fpr, and the coolant temp sensor while your in there

FPR looks good. Replaced the vacuum line with some clear tubing to look for fuel at idle; nothing.

Replaced AMM with known good one, no change.

Tried to check fuel pressure post-filter but our gauge fitting is larger than the shrader valve. Bout to pull the fuel filter and see what comes out..

OK, time for an update.

I've checked all the basics except for a compression test (I hope I didn't **** it up THAT bad! )

Priming it a couple times with the key, I have 50 psi fuel pressure pre-filter and just installed a brand new filter.

I've checked the cam timing and all the marks are aligned so I don't think it jumped a tooth, which was my best guess before.

I should note that the engine definitely sounds different when cranking now compared to before this little incident. Before it would crank for a good 4-6 revolutions before it fired, and sometimes I'd have to stop cranking then turn the key again, at which point it always fired up immediately.

Now when I crank it, it doesn't seem to have the same compression event sounds as it did before, and it fires almost immediately every time. Then it barely idles and generally runs rough as mentioned above.

I know this is far from scientific but ya know how you just get in tune with the sounds your car makes and when something changes you notice it while others think you're crazy? That's what's going on here, though my brother made the same comment I did about the different sound of things while it's cranking.

I really thought it had jumped a tooth or three on the timing and wasn't building any compression as a result of that, but everything looks good on that front. The timing belt has 68k miles on it, appears in good condition (don't they all though) and all the timing marks appear to be lined up.

This clearly isn't a fuel pump, FPR, AMM or vacuum leak issue. I have fuel pressure and the plugs are wet after cranking. I have spark. FPR is good. Unplugging the AMM makes no difference to the situation except maybe making it idle a little worse, and swapping in a good one changed nothing. Before when I'd gotten water inside the AMM circuitry and another time when I'd blown an intercooler hose nearby, I was able to unplug the AMM and "limp" home in LH's safe mode. When this issue occurred out on the road and I unplugged the AMM, the car was barely able to move under its own power (and it still can't).

I apologize for the verbose posts--I'm still learning the intricacies of the 9 series, the B230, and LH2.4, so I want to make sure I cover all my bases here while I attack the learning curve involved with a "new" car.

Thanks in advance for any help y'all can provide.

Also, I cleared the codes on A6 I believe it was, and restarted the car and let it idle for a few minutes and no new codes appeared.

At this point I'm really beginning to fear a blown head gasket, though all the fluids continue to look normal.

Blown head gasket?

I realized this morning that a strange occurrence about a week ago may have been a symptom slapping me in the face (literally) and I'd overlooked it:

I started the car dead cold in the morning and ran it for all of 20-30 seconds to drive into the shop. I yanked the airbox and one of the metal clamps hooked around the overflow hose running from the radiator to the reservoir. This resulted in extremely pressurized (but cold) water/coolant spraying me from the crotch to the forehead.

I thought of how weird this was, that the engine was only running for a few seconds and built up that much pressure, but didn't think much more of it.


Also, some more back info on this car. It had a pretty seriously clogged exhaust system (cat + cat pieces in muffler) when I bought it. So much so that the front of the #1 exhaust manifold gasket had literally disintegrated from the heat and pressure (the front nut backed off a little and that's all she wrote). I'm wondering if the engine being unable to evacuate all that heat would have prematurely blown the head gasket, and my foray into the land of 1 bar boost just finished it off...

Either way I'm about to go prepare the shop for a head gasket R&R. If anyone has ANY other opinions/suggestions on this I'd really appreciate it.

944Turbo said:

I realized this morning that a strange occurrence about a week ago may have been a symptom slapping me in the face (literally) and I'd overlooked it:

I started the car dead cold in the morning and ran it for all of 20-30 seconds to drive into the shop. I yanked the airbox and one of the metal clamps hooked around the overflow hose running from the radiator to the reservoir. This resulted in extremely pressurized (but cold) water/coolant spraying me from the crotch to the forehead.

I thought of how weird this was, that the engine was only running for a few seconds and built up that much pressure, but didn't think much more of it.


Also, some more back info on this car. It had a pretty seriously clogged exhaust system (cat + cat pieces in muffler) when I bought it. So much so that the front of the #1 exhaust manifold gasket had literally disintegrated from the heat and pressure (the front nut backed off a little and that's all she wrote). I'm wondering if the engine being unable to evacuate all that heat would have prematurely blown the head gasket, and my foray into the land of 1 bar boost just finished it off...

Either way I'm about to go prepare the shop for a head gasket R&R. If anyone has ANY other opinions/suggestions on this I'd really appreciate it.

Click to expand...

I'd diagnose it before you replace it. I'm assuming you still have not done a compression test? It'd be a bummer if 4 hours later the same problem still exists.

Forgot to mention, I'm waiting for the compression tester to be returned while I charge the battery and clean the shop up a bit. I'll have to skip cylinder #3 as I found out a couple weeks ago that some genius had cross threaded the spark plug in the worst I've ever seen. I sort of have a "new" 530 head lined up and was planning on doing this job as preventative maintenance anyway, but I will run a compression check on it before teardown.

slap a "spark plug hole repair sleeve" in the #3 hole - *then test the compression

http://www.amazon.com/Perma-Plug-1-25-Spark-Plug-Repair/dp/B0025PMJHA/ref=pd_rhf_se_p_t_1

pull ALL of the plugs and PRESSURIZE THE COOLING SYSTEM

Unfortunately I no longer have access to those kinds of tools.. though I want to say NAPA carries the Stant kit that will work with our reservoir caps.

Anyway, first 2 cylinders read 0 and 0 for compression but I'm not convinced its not a gauge issue since the one I'm using is from the 70s..

944Turbo said:

Unfortunately I no longer have access to those kinds of tools.. though I want to say NAPA carries the Stant kit that will work with our reservoir caps.

Anyway, first 2 cylinders read 0 and 0 for compression but I'm not convinced its not a gauge issue since the one I'm using is from the 70s..

Click to expand...

Try pressurizing the gage with compressor air and see if it responds. Generally a faulty gage wont read zero if there is any compression at all, it will just be off.

Lando said:

Try pressurizing the gage with compressor air and see if it responds. Generally a faulty gage wont read zero if there is any compression at all, it will just be off.

Click to expand...

That's a good call. The gauge "worked" but the valve was messed up and wouldn't hold pressure so I could read it after cranking though.

An Update...

So, went ahead and pulled the head this evening. Think I found the problem...











I can honestly say this is the worst gouge between cylinders that I've ever seen. Looks like the previous owner was driving the car like this for quite a while. Funny that it never ran hot or anything suspicious, other than the funky idle and eventually dying out on the road.

Looking back, I remember noting on the initial test drive that the car didn't seem to make as much torque just idling around and at part throttle compared to other B230FT cars I've driven. I just chalked it up to the differences between similar cars. Hopefully the new/freshened up top end fixes all that.

944Turbo said:

So, went ahead and pulled the head this evening. Think I found the problem...
I can honestly say this is the worst gouge between cylinders that I've ever seen. Looks like the previous owner was driving the car like this for quite a while. Funny that it never ran hot or anything suspicious, other than the funky idle and eventually dying out on the road.

Looking back, I remember noting on the initial test drive that the car didn't seem to make as much torque just idling around and at part throttle compared to other B230FT cars I've driven. I just chalked it up to the differences between similar cars. Hopefully the new/freshened up top end fixes all that.

Click to expand...

HAHA yeah you gotta try hard to take a chunk outa the head like that.

Well used 530 heads are a dime a dozen. If you got the cash, do some headwork on the "new to you" head while your at it.

That must be the worst headgasket failure I have seen Surprising that you noticed nothing really "off."

Haha, I know right?

I mean I figured it was just misfiring in #3 because that spark plug was severely crossthreaded and was at a weird angle, so its not like it was running 100%, just not as bad as id expect for such a serious HG failure.

My theory is the misfire sort of feeling was the gasket failure between 3 and 4 (duh) and when it finally breeched a coolant passage is when it let go and began bleeding into the other cylinder(s) and I lost all power out on the road. It makes sense since it was under heavy load when it let go.

I'm assuming that it must have been running for quite a while with the first failure in order to create that groove between 3 and 4, which must be a good 1/8" deep or so. Worst I've ever seen by far.

And to think I just took it on a 600 mile trip a couple weeks ago with no problems other than only averaging ~20mpg. Ain't that just like a Volvo.. (or a Land Cruiser). Man I love these cars..

944Turbo said:

It had a pretty seriously clogged exhaust system (cat + cat pieces in muffler) when I bought it. So much so that the front of the #1 exhaust manifold gasket had literally disintegrated from the heat and pressure (the front nut backed off a little and that's all she wrote). I'm wondering if the engine being unable to evacuate all that heat would have prematurely blown the head gasket, and my foray into the land of 1 bar boost just finished it off...

Click to expand...

Yes....
you think the bottom is ok??>>Looks prty deep there..
Just change firing order and go three cylinder.