Bought a 745i and it has almost zero boost!

[thecarousel]

Hi,

I bought a 745i yesterday and it has an issue with almost zero boost. On full throttle it might hit .05-.1 bar of boost but that quickly drops to 0. The car struggles to get up to speed. The previous owner stated that the issue started when the car sat for a few months.

I have done the following:
I pulled the wastegate off and made sure it wasnt stuck.
I smoked tested the system and found no leaks.
Tested the boost gauge.

Other observations:
idle seems a bit high in park (1000-1100RPM Warm) but normal in drive.
I can hear the turbo spooling.
Car starts up quickly and sounds healthy.
15-17lb of vacuum at idle in drive.

It seems like something would have to be something pretty major to prevent any boost from building. Any ideas on what to check next?

[yert315]

There is a similar thread a couple posts down. Read trough that for possible culprits.

What year is your 745?

Check your boost solenoid/sensor. Mounted on the AFM. You can replace it with a Volvo unit. That diy is posted here somewhere.

[thecarousel]

That sensor is new and was just replaced.

Is the diverter valve and that solenoid the same thing?

There is a similar thread a couple posts down. Read trough that for possible culprits.

What year is your 745?

Check your boost solenoid/sensor. Mounted on the AFM. You can replace it with a Volvo unit. That diy is posted here somewhere.

[yert315]

What year is your car? Motronic 745s (1983+ if i recall correctly) did not have a bypass valve.
The solenoid controls the wastegate whereas the bypass valve recirculates pressure back into the intake once the throttle is closed.

[thecarousel]

It's a 1985. The sensor appears to be working correctly and is hooked up properly.

[Hit Man X]

Well... it is not a sensor. It is a solenoid.

What fuel is being used in it?

What do you mean you 'I smoked tested the system and found no leaks.'

Idle spec is 800rpm hot.

Interested you can hear the turbocharger, the K27s are really quiet.



Start with posting pictures from under the hood. Many of them. With routing of the vacuum lines.

[gigi]

There is a similar thread a couple posts down. Read trough that for possible culprits.

Yes it's seem to be similar problem to my engine...

[Hit Man X]

Yes it's seem to be similar problem to my engine...

You are also missing critical items to the system and have seen only a few pictures of the swap.



Original poster will help us by uploading piles of photos. CA cars are the worst when it comes to incorrect vacuum line routing and bullshit added under the hood I have ever seen and restored to working order.

Probably want to try another boost and vacuum gauge. 17" in drive is odd, I can see 17-18" in neutral/park only.

These cars run just under 8 sec 0-60mph stock. They are nothing to write home about. When you have the system in limp mode, you have about 2psi and no power enrichment in my experience.

[kojo96]

In for images- Didn't know there was a 745i for sale locally-----

[thecarousel]

Sorry for my lack of initial detail. I appreciate the advice thus far despite the lack of information from me.



The solenoid is new, but I will test it tomorrow by applying 12v to the contacts.

It has a fresh tank of 91 octane. It also has a new in tank fuel pump and injectors (they are the correct flowrate).

I used a smoke tester at 5psi and searched for any obvious leaks. I found no leaks in any of the charge pipes or vacuum lines.

Is the idle manually adjustable? I am guessing that the high idle is an indicator that something is wrong.



Below is a link to an album that contains photos of the engine bay (Bonus exterior pictures on the bottom). The knock box has the vacuum line hooked up. Also, the HVAC system has all of the pots and pump replaced.
https://imgur.com/a/rmHWk

The car wasn’t for sale public, I picked the car up from a good friend for an absolutely killer deal. It is a 1985 executive package. I have the order/build sheet and some other cool documentation that I will upload later.

Thanks again for all of your guys assistance!

Well... it is not a sensor. It is a solenoid.

What fuel is being used in it?

What do you mean you 'I smoked tested the system and found no leaks.'

Idle spec is 800rpm hot.

Interested you can hear the turbocharger, the K27s are really quiet.



Start with posting pictures from under the hood. Many of them. With routing of the vacuum lines.

[gigi]

Hello,

Where goes this vacuum line with bleue one way valve?

I don't have this on mine...

m3Ebe41.jpg
Thanks

[nikoor]

Hello,

Where goes this vacuum line with bleue one way valve?

I don't have this on mine...

m3Ebe41.jpg
Thanks

It is one-way valve for HVAC system, it prevents boost pressure entering vacuum system. It connects between intake manifold and T-piece. Other two components connected are electric vacuum pump and vacuum tank (sixpack).

[gigi]

It is one-way valve for HVAC system, it prevents boost pressure entering vacuum system. It connects between intake manifold and T-piece. Other two components connected are electric vacuum pump and vacuum tank (sixpack).

Ok, so it's normal I don't have this because I don't have HVAC

@thecarousel, how have you proceed to do the smoked test? You have put smoke before or after AFM ?

[thecarousel]

I tested both after the AFM and after the intercooler.

Ok, so it's normal I don't have this because I don't have HVAC

@thecarousel, how have you proceed to do the smoked test? You have put smoke before or after AFM ?

[gigi]

I tested both after the AFM and after the intercooler.

Ok, and you don't see smoke through this little vacuum line ?:
Vacuum line.jpg

Because...something I don't understand...
Vacuum line.jpg
On this scheme, I have draw this vacuum line in green, and all pressure in the manifold goes directly in the elbow between AFM and inlet turbocharger...which is permanently in vacuum!
Do you have one-way valve on this line?

[Hit Man X]

First problem I saw is that thermo vacuum switch. Delete that. You are to have three on the tstat housing. CTS, TTS, and the cluster gauge.

Cannot tell how your boost noid is hooked up (I think yours is correct), but it is simple - Bottom is suction alu pipe between AFM and turbocharger. Upper outer is WG, upper inner is boost signal from compressor housing.

Post more when back from alignment shop.



Car looks sharp. Does it have SA code 440? We figured out that 'non smoking package' is actually the Executive code.

[gigi]

Cannot tell how your boost noid is hooked up (I think yours is correct), but it is simple - Bottom is suction alu pipe between AFM and turbocharger. Upper outer is WG, upper inner is boost signal from compressor housing.

Hit Man, and what about the electrical connector? Is there any sense?

Thanks

[Hit Man X]

Small vacuum hose from intake manifold to the valve cover is correct. No check valve. It is part of the PCV or breather system.

The green wire on boost solenoid is always hot with key on. Same as positive side on ignition coil. This runs right off the ignition switch and trips main relay to close and send power to red/white and red/blue wires.

The black wire is grounded or pulsed by the knock regulation and boost control box. That unit has a one way check valve to it and needs to be open to the atmosphere. Also the hose into the box degrades with age and leaks.

[thecarousel]

Small vacuum hose from intake manifold to the valve cover is correct. No check valve. It is part of the PCV or breather system.

The green wire on boost solenoid is always hot with key on. Same as positive side on ignition coil. This runs right off the ignition switch and trips main relay to close and send power to red/white and red/blue wires.

The black wire is grounded or pulsed by the knock regulation and boost control box. That unit has a one way check valve to it and needs to be open to the atmosphere. Also the hose into the box degrades with age and leaks.

I will check the wiring to the solenoid this evening. The check valve is working properly and the line that runs to the knock box is in good shape. Is there a line inside of the box I need to replace?

Thanks!

[Hit Man X]

That roughly 1/4" vacuum hose degrades from check valve to box. Not sure how car will drive with it tatty, I replace on all builds as standard procedure with silicone.

More pics can help us. I am sure you have a simple issue at hand.

Buy a wideband too. The car could be so lean it is knocking like crazy and going into limp mode. BMW specs 14:1 hot idle on a WBO2. This will lean cruise in the 15s, NORMAL, and do mid 12s wide open. If AFM is leaned for idle emissions test, part throttle and boost tip in super lean.

[thecarousel]

The hose from the check valve to the box has been replaced with a rubber line. I ordered some silicon and will replace it once that arrives.

What photos would be of the most help?

I have access to a wideband, I will pick it up and install it this weekend.

That roughly 1/4" vacuum hose degrades from check valve to box. Not sure how car will drive with it tatty, I replace on all builds as standard procedure with silicone.

More pics can help us. I am sure you have a simple issue at hand.

Buy a wideband too. The car could be so lean it is knocking like crazy and going into limp mode. BMW specs 14:1 hot idle on a WBO2. This will lean cruise in the 15s, NORMAL, and do mid 12s wide open. If AFM is leaned for idle emissions test, part throttle and boost tip in super lean.

[Hit Man X]

I guess anything related to the engine. Sounds weird, but there may be things others see that I do not. I do not know all and never will.

Is the AFM correct? 0 280 203 022? You have a 0 261 200 013 ECU too? Fuel/timing switch in stock location?

Touch all those charge couplings by hand, sounds silly. I had one loose on my old Ljet. Cause piles of grief. Also the hot side right at the turbocharger to the IC on my 10/84 fell apart when I removed it. ! The car is nearly 40 years old. Anything rubber needs to have been changed a few times by now.

[thecarousel]

I dropped the car off at my favorite BMW shop today to diagnose the issue.

It turns out it was a clogged catalytic converter.

I would like the car to have a nice sound but not be too loud.

Thoughts on a 3" exhaust with a new cat, resonator, and magnaflow muffler?


Thanks again for all the help!!!

[Hit Man X]

What is loud to you?

[thecarousel]

I just confirmed. The car does has SA440.

Car looks sharp. Does it have SA code 440? We figured out that 'non smoking package' is actually the Executive code.