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92 740T will start fine once, then sputters out and will not restart and stay running

Current state of vehicle: It will start, but initially struggles with any throttle input for the first few minutes. After idling and reaching temp, seems to take throttle input, but will randomly start having throttle issues when put into drive or reverse. Also noticed a high pitch whistle from passenger side engine bay on initial throttle input, which goes away at higher rpms than 2k. Checked and confirmed that turbo spins freely and is not having excessive movement. Next steps will be smoke testing again to check if any leaks have formed after getting vehicle back up and running. Getting good fuel, good spark from what it seems, but assuming I am getting random bursts of excess air which is preventing combustion and causing engine to flood until stall. Feels like one thing gets fixed and another gremlin pops up.
 
Question for all who have a manual boost controller installed, where in the turbo vacuum lines are you tapped into? The only thing that has really changed between the successful test drive and now is that I reinstalled the manual boost controller between the intake and the turbo after checking a write up on here about mbc installs, but I could have sworn that before these issues and removing the mbc initially, the controller was between the wastegate and the internal bov, not the intake. Could it be possible that I am big dumb and it is pushing too much air into intake at low throttle and throwing of afr in the cylinders enough to cause it to die and flood? Or am I grasping at nothing here?
 
If you’re talking about the compressor bypass valve on the compressor side that wouldn’t work. That opens under vacuum, referenced off the intake manifold.

You know there’s a boost reference nipple right on the front of the compressor housing, right? Or should be anyway. Put the MBC between that nipple and the wastegate actuator. I suppose it’s fine to reference from the intake manifold instead, and maybe there’s a situation where that’s better, but I can’t think of one right now.
 
ortho stice said:
If you’re talking about the compressor bypass valve on the compressor side that wouldn’t work. That opens under vacuum, referenced off the intake manifold.

You know there’s a boost reference nipple right on the front of the compressor housing, right? Or should be anyway. Put the MBC between that nipple and the wastegate actuator. I suppose it’s fine to reference from the intake manifold instead, and maybe there’s a situation where that’s better, but I can’t think of one right now.
Click to expand...
That is how I had it installed previously, but when I went to throw it back in, I must have been reading the wrong write ups and put it in the wrong spot. Gonna swap it around tonight and see what happens.
 
Swapped mbc orientation, pulled plugs and the gap was a little wide for my likings so i gapped them down, and after letting it start up and idle, car is moving. It will still think about bogging if I stab throttle and let off, but as long as I am conscious of what I am doing while driving, it will drive just fine. I have noticed that it seems to want to take off in 2nd gear unless i force it into first with the gear select, so I will check tranny levels again since I never was able to fully run it after doing the radiator. I know my compression has never been the greatest, so wondering if that might be the cause of it bogging when stabbing throttle, but still planning on replacing current vacuum lines with silicone line. At the very least, it is driving now and feels decent if I make sure to take off in first.
 
baddecisionsmadedaily said:
Swapped mbc orientation, pulled plugs and the gap was a little wide for my likings so i gapped them down, and after letting it start up and idle, car is moving. It will still think about bogging if I stab throttle and let off, but as long as I am conscious of what I am doing while driving, it will drive just fine. I have noticed that it seems to want to take off in 2nd gear unless i force it into first with the gear select, so I will check tranny levels again since I never was able to fully run it after doing the radiator. I know my compression has never been the greatest, so wondering if that might be the cause of it bogging when stabbing throttle, but still planning on replacing current vacuum lines with silicone line. At the very least, it is driving now and feels decent if I make sure to take off in first.
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Is the bogging from idle, while driving, both?

Is the throttle/switch set correctly?
 
Holds idle well, but when put in drive, if I hold the brake or if I am sat at an uphill, once I give gas, it stutters for a second, and if i give more than like an eighth of a pedal push, it will bog and most of the time die out. I have read that people have issues with the bougicord wires having too much insulation at the end and needing to be trimmed, as it almost feels like I lose spark for a second.
 
Throttle switch is clicking right after turning throttle by hand, so guessing that is good. I am feeling like next step is going back through the vacuum system and rechecking for leaks. Found the elbow for the line to the cruise control was old and falling apart, and it also couldn't hurt to clean up the pcv.
 
Still haven't had a second to go out and mess around with the car other than making sure it starts up, but I have noticed that every time that I do start it up, it has a slowly rising idle from start. Seems like vacuum leaks might be my final battle with this. Hopefully.
 
Smoke test the induction system.

You could spray around with brake cleaner and see if you can get the idle to change, stall, stumble etc, and you have found a leak.

I don't see where you ever measured the 02 sensor voltage like a mentioned a couple of times.

CODES??
 
Man, I really need to stop looking at this car like a chevy 350, and start respecting what it does with the ECU. Didn't realize how much of an issue the O2 sensors could cause on these rigs, as well as I could have sworn that I had replaced the sensor but looks like I was wrong. Had the engine running and with the sensor plugged in, every time I would hit throttle it would stumble, but if I unplug the sensor, seems like engine will catch every time. Have not yet gotten another multimeter (first one I bought did not have good enough refresh rate to read the square wave properly) to test the system, but I am going to get a new O2 sensor for the system since this one appears to be the original unit.
 
It is not a square wave! It would be a sine wave at about 2000 rpms. At idle it would be an ugly wave oscillating up and down from 0.1V to 0.9v on a warm engine.



0.9V pegged is rich (or bad sensor) . 0.1v pegged is lean (or bad sensor).


CODES!!!???????????
 
I was seeing flat .9 with the meter i had, but as far as codes, other than a 113 for the speedometer signal, it hasn't given me any codes after letting it run. Not sure if there's just bad connection at the test port. But I haven't gotten others than the 113.
 
Either bunk 02 sensor, rich mixture from a failed component, OR the ECU is defaulting to full rich due to a fault condition. I used to not believe in "limp mode", but I found my 1990 740 GLE 16V was pegging the 02 sensor rich when it was throwing codes.

Shotgunning a new 02 sensor in there at this point cannot hurt. Then measure the voltage again warm and see if you can get it to oscillate. I would spend 20 seconds with a test lamp and confirm it powers up between the two white wires for the 02 sensor. Thats the heater power and ground circuits.

I personally have never seen an Electronic Coolant Temperature sensor (ECT) fail, but maybe that one you put it is the wrong one, or no good outta the box. You would have to backprobe at the ECM and check voltage.

You also say you smell fuel. MAYBE you are smelling a rich condition.
 
ZVOLV said:
Either bunk 02 sensor, rich mixture from a failed component, OR the ECU is defaulting to full rich due to a fault condition. I used to not believe in "limp mode", but I found my 1990 740 GLE 16V was pegging the 02 sensor rich when it was throwing codes.

Shotgunning a new 02 sensor in there at this point cannot hurt. Then measure the voltage again warm and see if you can get it to oscillate. I would spend 20 seconds with a test lamp and confirm it powers up between the two white wires for the 02 sensor. Thats the heater power and ground circuits.

I personally have never seen an Electronic Coolant Temperature sensor (ECT) fail, but maybe that one you put it is the wrong one, or no good outta the box. You would have to backprobe at the ECM and check voltage.

You also say you smell fuel. MAYBE you are smelling a rich condition.
Click to expand...
Going to get an o2 thrown on as soon as I can get one ordered in from IPD. Had some talks with John Dally, and I think it was mentioned through here at some point, but the air hose from the turbo to the manifold when failing will that suck closed internally to where I wont really see it closing? I know it has some sheathing along it, but was not sure if it was something that had an outer and inner lining situation. Have not visually seen the hose collapse, but it is also one of the few hoses I did not replace when I purchased the car.
 
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