What happened to my engine?

[Otter74]

Last Sunday I headed out to go to a show and, while in traffic on I-94, I downshifted, got a small backfire out the intake blowoff valve (this happens every once in a great while - the PO who installed the EFI has tuning notes that it was doing that many years ago), and the car fell on its face, with no torque. I was giving it full throttle to hold 60 in 4th on flat ground. It recovered for a minute or so, then lost torque again. I pulled over, shut it off, and called AAA to get it taken home. After six years and 30k+ miles, it’s the first thing that’s ever happened to the car.

Car is a 1980 SC running on a Megasquirt MS2 controlling fuel and ignition, with Ford EDIS ignition. Unfortunately I was planning to take the car on the road trip to CO/UT/AZ that I’m leaving on this morning, which obviously isn’t happening. I haven’t had a lot of time prior to the trip to look into it. I did manage to sort out some firmware issues with TunerStudio and my PC laptop and got TunerStudio running and talking to the car for the first time (I’ve never messed with it before because I never needed to.)

After shutting the car off the car would crank and barely run and then shut off, before going to crank-no-start. In the garage, a night or two later it did start and run, albeit barely and badly.When it runs it idles at about 300rpm, is barely responsive to throttle input (there’s a second or two of no response) and won’t go above about 1000rpm. It’s run a few times but I don’t want to run it unnecessarily until I understand the problem. Sometimes it’s crank-no-start or dies after a few seconds.

Unfortunately getting ready for my trip, work, etc. has meant I’ve had very little time to spend on the car this past week. Of course you start with the basics - fuel, air, spark, compression. The car will run, so it’s at least getting *some* fuel (I initially wondered if I was simply out of gas - it’s happened before - but it wouldn’t be running if I were). I wanted to run Tooth Logger on TunerStudio to see if the CPS was reading correctly, but I’m unable to do data logging right now - this might be due to a 3.3.3 / 3.3.4 firmware mismatch. When I get back I’ll pull the plugs and test for spark (but, again, it will run), and also read them. Then check compression on each cylinder.

Here’s a video I took of the engine running:

(That was the first time I’d heard that rattling sound, and I shut it off. It sounds as if something was rattling around in the intake.)


Here’s the TunerStudio dashboard:

Looks rather lean for idle?

Possibly related: What is this low undertone in my engine sound?

I won’t be able to work on this for a couple of weeks, but I’d like to get the collective’s thoughts on this. Giant bummer since I was really, really looking forward to taking it to CO/UT/AZ, but by now I’ll be happy if it’s not $$$. At least I can fix a lot of s**t myself.

[dannobee]

Is the bypass valve leaking? Is the air box cracked?

When it's idling, add a shot of carb spray to the intake and see if the engine speed picks up and smooths out. If so, start adding a shot around the intake ports and such, looking for a vacuum leak. Engine speed will pick up when you find it.

[brighton911]

Your WB sensor may have given up the ghost. The mixture show super lean yet the PW is right up there.

[Otter74]

Originally Posted by dannobee

Is the bypass valve leaking? Is the air box cracked?

When it's idling, add a shot of carb spray to the intake and see if the engine speed picks up and smooths out. If so, start adding a shot around the intake ports and such, looking for a vacuum leak. Engine speed will pick up when you find it.

Good idea, thanks - I can try that before I leave this morning.

Originally Posted by brighton911

Your WB sensor may have given up the ghost. The mixture show super lean yet the PW is right up there.

What might have led to it giving up so suddenly? And how can I test it?

[Dan J]

In all the Porsche DME trouble shooting charts the first question is:
Is the engine in perfect mechanical condition?
I think it behooves you to ascertain this first
I would do a leakdown test and then physically check cam and ignition timing
I don't like that noise

[s5uewf]

I agree with above. looks like AFR is very lean. May be sensor, wiring harness for sensor, or other air leak that is large enough prevent the EFI from compensating (like an intake manifold gasket, etc.)

Do you have a fuel map/VE map you can access at idle, for example? Is it possible to turn off the WB sensor and manage idle AFR directly with the map? It may be one way to test to include/exclude sensor and sensor wiring...

[proporsche]

your alternator belt is way loose. The noise could be your alternator. Remove the pulley&belt, start it again see if the noise is there. .....if it still noisy i`d look at the chain rails and e.t.c.
Do not know about megasquirt......

Ivan

[Otter74]

I am suspicious of an air leak. Sound referenced in my earlier thread (which slowly got worse over time) sounded to me like an exhaust leak or obstruction, e.g. chunks of cat matrix (it’s gutted but I’ve never actually looked inside) or muffler baffles. Could not find obvious leak when I was under the car before changing the oil the other week. Possible backfire was through exhaust and it ble something out, I suppose. I did put a screwdriver to alt housing and didn’t hear any untoward noises, and no charging issues. OTOH thanks for pointing out belt tension - I wondered about that.

I do have fuel and VE maps that I can look at at idle, though it was a no-start when I went to try a little bit ago (sometimes it almost turns over or runs for a moment, sometimes it just cranks, sometimes it runs. This time was no-start and I was flooding it so I stopped. Good idea on turning off the O2 - I’ll see if I can do that. I’m a smart bear but I’m a noob at using TunerStudio. I wish this had happened a week earlier so I had time to diagnose before my trip!

[Marwil]

Pulse width is really high for attempted idle conditions. Check the vacuum line feed to the fuel pressure regulator, the intake backfire may have blown the hose off the the throttle body nipple. If it is indeed running super rich because of an over fueling issue then the plugs may be fouled also. It’s got to be something simple to account for the sudden change.

[Phillip_G]

I also would suspect that the backfire caused a vacuum leak somewhere. Your MAP reading at idle is in the 70's which seems high. Do you have datalog when it was running well for comparison?
Since the pulse width values look reasonable, I suspect that the MS2 is set to deliver fuel based on the tables rather than adjusting based on AFR feedback, resulting in the way too lean result.

[Phillip_G]

Actually, we can't really know what reasonable PW values might be without knowing the injector delivery volume, so having a good datalog would really help with the diagnosis.

[Otter74]

What’s an expected pulse width for idle? Per the above it’s around 6ms. And mixture is really lean (like 19:1), not rich. I did misread as rich initially due to mental default interpretations of graphic. No data logs at all - I never got TS set up until now. Can’t data log until I resolve software issue, suspect updating firmware on both TS and car will do it. I did look at the vacuum line to the FPR and I don’t think that came off, but I’ll check again before I leave. Blowoff valve does not appear to be leaking. If I could get it to run now I’d go spray all the possible gaps in the intake. But damn I need to leave, I have a 14-hour drive to CO (LOL). It’s hard to let go mentally of being able to take this car on the trip!

[Otter74]

Unfortunately it’s not starting this morning (it’ll just catch for a bit but won’t stay lit) so I’m going to have to defer this until later. I’m tempted to wait a day to leave because I badly want to drive this car, but I have plans in Denver tomorrow.

[dannobee]

You can check the O2 sensor by monitoring the output, then adding a shot of carb spray to the intake. It should respond almost instantly by going full rich. If it doesn't respond or it takes more than a couple of seconds, it's suspect.

[proporsche]

if it does not start it is a good time to address the noise from the alternator and loose belt...i think you did ask about the noise right??
Ivan

[Otter74]

I did have time to unplug the sensor and try to start it again. No change, which tells me that whatever the problem is it’s not that. True, the sensor isn’t needed for starting but if that was all that was wrong it would start every time before running badly. I doubt the MS is looking at it at all at idle rather than just using the VE table. At any rate I’m on the road so will have to revisit later

[pmax]

Running like crap after a backfire ?

Check for leaks.

[Marwil]

The thing is that if an intake backfire occurred it could blow off the vacuum hose that controls the fuel pressure regulator (FPR). Here is my hypothesis - not only is there an air leak but the FPR is getting a false signal. Because the vacuum hose is detached the FPR sees normal atmosphere pressure just as it would if you were running wide open throttle. This will have the effect of reducing flow back past the FPR and increasing the fuel pressure itself. Furthermore if the MS2 is using the same vacuum source it will also think it is operating at WOT and send a higher that required pulse width of now higher pressure fuel.
I could be dead wrong on this but it is worth looking into - Occam's razor and all.

[brighton911]

I think Marwill is on track to your solution. A nice easy cheap one at that.
I know from experience the O2 sensor will show lean when they come to the end of their life cycle. Placement in the stream, orientation, oil consumption, running rich and time are all factors in their life cycle. And as mentioned, testing is possible.

[Otter74]

Honestly I’m not certain it was in intake backfire - could have been out the exhaust. And occasionally backfires through the exhaust over the years would comport with that odd undertone coming from the exhaust, perhaps. I can test the O2 (it’s an Innovate wideband) when I get home, but I’m not sure an out-of-range sensor makes sense as a cause given the sudden onset of symptoms. I did check the vacuum hose from the intake to the FPR and it’s fine. I do not discount an air leak, however. Some time last year or so I started getting an irregular high idle that suggested such. I recently found that the intake elbow was loose (it wasn’t obvious) and tightened it, which helped but didn’t fix the high idle. I’ll borrow a leak tester when I’m home.