Not really sure where to go with this next... (intermittent no start/power loss)

[Redline]

Like the title says,

I have been experiencing an ongoing issue that has me at the point of throwing in the towel. (no shop wants to deal with it or says its fine)

The Problem:

1) When either hot or cold, intermittently when starting the vehicle it'll either crank then die immediately and require a second crank (starts flawlessly)
2) When either hot or cold, intermittently when starting the vehicle it'll start but barely and kind of chug at a low rpm and build up rpms like its starved for fuel or not firing on a cylinder (revolving rpm drop/surges up) this happens for all of a second or 3) then idles fine and runs fine.
3) Starts perfectly.

Also intermittently car will fell like its lost low end torque when getting on it, or in power band top end doesnt pull as strongly to redline but pulls ok down low. you can literally drop a gear and floor it and it'll take offf but not that hard, let off and then punch the gas again after cruising for a sec and itll roast the tires/take off like a bat out of hell....

There is no CEL

A little bit of a back story:

2 years ago did rod bearings, valve adjustment and vanos rebuild (seals, bolts, timing chain guides, the whole thing, also soldered the solenoid to fix loose contacts as well and cleaned the valve block) car ran better than it ever has, carefully drove it 1k miles increasing rpms 1k every 100 miles and did first oil change at 1k, after that car fricken ripped with the new vanos overhaul. no issues.

about 2k miles after this i go out to my car after work and go to start it, just a click and gauge cluster starts buzzing (battery dead) jump started it and it fired right up, drove it to a friends shop to replace the battery...after this even is when sh!t started rolling down hill and components have been dying off here and there. idk if it was a voltage spike or what have you but ive replaced the following components to make a long story short...

-vanos rebuild D300 hub, besian seals, upper timing chain guide(s), updated bolts, soldered solenoid for broken contacts and cleaned valve body
-rod bearing and associated seals/gaskets
-valve adjustment
-throttle position sensors (front and rear on actuator) lubed linkage and cleaned and lubed throttle bodies)
-crank sensor
-new plugs
-new coils (eldor)
-thermostat and fuel pump were replaced about 60k miles go back in 2015 (pump holds pressure not the check valve i though it would be so not wasting money replacing it again)
-new fuel injectors (bosch) one was leaking which i though was the problem...
-new fuel pressure regulator
-new fuel filter
-new starter (bosch)
-new ebox fan (dme blower motor for cooling)
-egt sensor (had a fault for it, old one was dead)
-coolant temp sensor (ect)

all parts replaced had a verified failure and this was after that dead battery incident.

all codes that show up randomly now are not present and dont trip the cel

most recurring code is cylinder 4 misfire (gets spark, gets fuel, connections to dme good, ground/power good, compression/leakdown good on this and all cylinders)

ebox fan (idk how i replaced it not even 10k miles ago and fault still shows up, fan turns on when i crank the car and shuts off after running for a minute on startup)

crank position sensor (new sensor, connections good, at a loss here probly due to mis-starts)

and i randomly got a o2 sensor slow to respond code that never came back (response good when checking scan too, afr's good, fuel trims good, idk whats up)

randomly engine temp will hang left a little bit but then center out so maybe thermostat sticking open again (bought a new one to replace again)


to top this off, when i change my oil after 5k miles it smells of gas more than usual (oil level never rises, boroscope down all cylinders show the same no cylinder looks fouled or washed out) new injectors so no leak...

not really sure where to go with this now. getting really annoying and embarrasing having a car that barely starts at times, and doesnt go like it should at times....

sorry for the long book i just wrote. but if anyone has any idea where to look im into suggestions.

even opened up the dme to check it to see if anything was burned up as i had a fault for injector driver 1 over temp (this is when i replaced fuel injectors as 1 was hanging open) as i though maybe one of the mosfets was fried, but found nothing. all relays have been replaced as well for fuel pump and dme.


also vanos is about as perfectly timed as i could get it, gets full range of motion on exhaust and intake side and adaptation is .02 deg. passes test every time.

[ATB88]

Sorry to hear about your frustration. I have complete empathy -- I've been chasing a few issues of my own for a while now and am also at a total loss for what to do as I've replaced and tested every component I could conceive of as causing a problem at this point. It's really frustrating to put so much work into your car and still be stuck with issues that take away from your enjoyment every time you drive it. I'm actually experiencing starting problems similar to yours, except mine has never yet completely failed to start (here). Really close to just rolling the car into the ocean and calling it a day, at this point.

I'm guessing you've checked that fuel pressure's okay? I recently monitored fuel pressure during startups and found that during the struggling/hard starts fuel pressure was 5 bar therefore probably not the problem. Might be worth a check just so you can 100% rule out the fuel pump, as that has more miles on it than anything else in your fuel system.

How old are your cam position sensors? I've read that they can cause intermittent startup and power issues even if they aren't throwing codes. While they maybe don't seem the most likely culprit for this kind of problem, you've ruled out the obvious things.. it's unfortunate how "tolerant" our cars can be to problems before they're bad enough to trigger a CEL.

[Redline]

Sorry to hear about your frustration. I have complete empathy -- I've been chasing a few issues of my own for a while now and am also at a total loss for what to do as I've replaced and tested every component I could conceive of as causing a problem at this point. It's really frustrating to put so much work into your car and still be stuck with issues that take away from your enjoyment every time you drive it. I'm actually experiencing starting problems similar to yours, except mine has never yet completely failed to start (here). Really close to just rolling the car into the ocean and calling it a day, at this point.

I'm guessing you've checked that fuel pressure's okay? I recently monitored fuel pressure during startups and found that during the struggling/hard starts fuel pressure was 5 bar therefore probably not the problem. Might be worth a check just so you can 100% rule out the fuel pump, as that has more miles on it than anything else in your fuel system.

How old are your cam position sensors? I've read that they can cause intermittent startup and power issues even if they aren't throwing codes. While they maybe don't seem the most likely culprit for this kind of problem, you've ruled out the obvious things.. it's unfortunate how "tolerant" our cars can be to problems before they're bad enough to trigger a CEL.

and you know i thought about replacing the intake and exhaust cam position sensor as thats the only thing on here that hasnt been replaced (would have been a hell of a lot easier if i did the intake one while i was doing the injectors..gotta pull #6 injector to get it out) just not trying to throw more parts at it but whatever...ive already rebuilt the whole car....every bushing has been replaced, struts, springs, driveshaft, differential, hubs, steering linkage, hoses, lines. etc. etc. too far into it now to get rid of it. wont get sh!t for it at 204,000 miles on an 02 steel grey vert 6mt haha...im officially married to this car. been driving my 750il in the mean time....i must love pain or throwing money away owning both of these cars for daily duty.

[Redline]

So got around to putting in the new thermostat. Power loss issue seems better...still has a hard start/stumble immediately upon start intermittently Like a cylinder is t firing for a sec. Cleared faults and will see what codes come back. Going to check every ground again. Just odd cylinder 4 keeps showing misfire codes when plug, coil, injector, compression, etc. are g2g...

[Redline]

Anyone? Keep getting cylinder 4 misfire When it does the hard start, once it’s running never misses. Mechanically everything is good, new plug new coil, only thing not replaced now is the cam sensors. But I’d doubt it would be just one cylinder unless the tone ring on the camshaft was the issue.

[Zekarus]

would check again the fuel pressure. maybe change your pre cat o2 sensors. can you borrow a dme to sort this out, even though you opened it. man i'm feeling with you. wish you all the best!

[poth2034]

Didnt see anywhere above if you replaced your maf or not. Try unplugging it and see if the car starts any easier or maybe even run better.

[slavik1988]

Didnt see anywhere above if you replaced your maf or not. Try unplugging it and see if the car starts any easier or maybe even run better.

The car won't start with the MAF unplugged.

[heinzboehmer]

The car won't start with the MAF unplugged.

Are you sure? I'm almost 100% certain I've started my car with the MAF unplugged on accident before. It threw a check engine light pretty fast, but the car started.

[Redline]

Sorry Forgot to mention maf is new too lol, I’ve replaced everything but the camshaft position sensors, icv, and actual throttle actuator on this engine.

[Redline]

Ordered a set of pre cat o2 sensors, car is running rich still even after the t-stat replacement. Will update thread after replacement. At 204k miles I’d think it can’t hurt lol. They are original so surprised they lasted this long.

[Redline]

Installed the new o2 sensors. Gas mileage and power are back...still have the starting issue.

that just leave both cam position sensors. And purge solenoid for what hasn’t been replaced lol. Or fuel pump check valve failing? Pump is 6 years old and about 80k on it...tested fine last 2 times I checked it though...

[SteelGreyM]

This sounds very similar to what my problem was. My head gasket failed but I never noticed because it was a tiny fail between cylinders. Kept getting harder and harder to start along with sluggishness. One day I had oil smoke out the exhaust.

you said you had a compression test done?

[ATB88]

Glad you're making progress with it, OP!

This sounds very similar to what my problem was. My head gasket failed but I never noticed because it was a tiny fail between cylinders. Kept getting harder and harder to start along with sluggishness. One day I had oil smoke out the exhaust.

you said you had a compression test done?

Given that my hard starting problem now sounds very similar to OP's, I'm curious about this possibility in my case. I did a compression test and found 179-180 on cyl 1,2,5,6, and 170ish on cyl 3, 4. Could this relatively small compression difference point to early headgasket problems? I had thought that these numbers were definitely nothing to worry about.

[Redline]

This sounds very similar to what my problem was. My head gasket failed but I never noticed because it was a tiny fail between cylinders. Kept getting harder and harder to start along with sluggishness. One day I had oil smoke out the exhaust.

you said you had a compression test done?

Compression test was about maybe 1-2psi difference between cylinders. That’s what I was afraid of. But it seems it happens more in the UK/Europe than here in the states.