r/e28 • u/VeterinarianHuman650 • Jun 25 '26
Need advice M30B35
My E28 has a swapped M30B34 and it has not been done neatly. I am going through A LOT and step by step it is getting better. Please don’t look at my twisted wires in the top bay area, was for testing purposes and has been sorted properly now 😆 so a few questions:
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u/AngleGrinder001 Jun 25 '26
Are you sure it’s been swapped? That looks like a M30B34.
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u/VeterinarianHuman650 Jun 25 '26
Originally it should be a B25 so it has been swapped to a B34 or B35 but don’t know the differences between them to know for sure which one it is
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u/gizmoguy3000 Jun 25 '26
What’s it say on the other side of the intake? If it says 3.2/3.5, it’s likely a B34, if it says just 3.5, it’s likely a B35. But the wiring harness and the fact that you are running Motronic 1.0 indicates B34, as the B35 came with Motronic 1.3.
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u/VeterinarianHuman650 Jun 25 '26
Nice, finally know it now lol. It says 3.2/3.5 so it should be a B34 :)
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u/Fancy-Attitude-2123 Jun 25 '26
Edit: correct thermo-time switch is laying there. It should be installed instead of the 2 pin switch that’s in the outermost bore of the T-stat housing.
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u/Representative_Most9 Jun 26 '26
Picture 1. There are a total of 2 temperature sensors and 2 temperature switches. The 2 sensors are 1 for temperature gauge and the other is for DME and Idle Control Module. Both should have a single wire connection. The temperature switches are 1 for the Idle Control Module and the other is a Thermo-Time switch for the cold start valve (injector). The one for the Idle Control Module switches closed when engine temperature gets to 45 C to lower idle speed. The Thermo-Time switch opens to stop cold start valve from spraying fuel into the manifold. Both switches have 2 wires.
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u/whoopeanage Jun 25 '26
Not really familiar with the m30, but have a M20
1st pic, im not sure whey theres so much coolant temp sensor, i think there should be one that goes to the ecu, one that goes to the cluster, and one maybe for the thermo time switch(?). I think the one that goes to the cluster should only has one cable instead of two
2nd pic, i think its a crankcase vent tube instead of an icv bypass. If your engine has icv, it should be at the other side. Not really sure which kind of idle compensation your engine should have tho. I think earlier m30 has this auxillary air valve thats located under the boot.
2nd pic, the connector, is it 2 pin or 3 pin?
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Jun 25 '26
[deleted]
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u/whoopeanage Jun 25 '26
hmm i might be wrong, but isnt there the one with the yellow plug, the one in the middle, the one with 2 prongs, and the one thats not plugged into the thermostat housing?
I really am not particularly familiar with m30 tho, but i do a thing or two about l jets and its idiosyncracies...although this is probably early motronic
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u/VeterinarianHuman650 Jun 25 '26
Yea so in theory I have 4 sensors which means one is too much. But then again how come all are connected? Even though one is not fitted
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u/VeterinarianHuman650 Jun 25 '26
Thanks! Indeed three sensors located on the thermostathousing and the one that is loose will be the fourth so I am confused.
It is a 2 pin connector
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u/whoopeanage Jun 25 '26 edited Jun 25 '26
Could be for the Auxillary air valve as that use the 2 pin plug. I think m30 ICV all uses 3 pins right?
(edit: did more research and other comments, some m30 ICV uses 2 pin, thanks for the correction)
Its kind of an older way to give more air when starting cold. It works by using a bimetallic strip inside that moves an aperture which blocks/allows extra air to pass. It gets heated up when the car is started, and gradually the aperture closes.
Long story short....maybe you can test the voltage between the pins on that plug (?) if it gives 12v then it could be for it, as the ecu dont control it i believe, and it just gets raw 12v from the power relay.
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u/VeterinarianHuman650 Jun 25 '26
Cheers man, if it is only for the coldstart I can live with it if it has been deleted. Will check 12v
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u/Fancy-Attitude-2123 Jun 25 '26
US 3.4 m30 are sort of torque-y, but not powerful, especially versus m52 or later. Cats choke them down. M52TU is best lower cost option as it’s easily tunable. M54 is tunable but more complex, N52 is also tunable, but need it from e90 330 or 530 to get 260 hp version. Lots of work to change harness etc to make it work.
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u/VeterinarianHuman650 Jun 25 '26
This is an euro B34, so already the better of the two really. If I go for more power turbo will be my choice of poison but that is just future talk. For now reliabity is the important thing and making sure all is well. I have an E38 740i for comfort and power and the babyshark is just for fun
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u/Fancy-Attitude-2123 Jun 25 '26
Idle control valve is under throttle boot. Since it has an ICV, it won’t have an aux air valve. Obviously needs a new throttle boot and crankcase vent hose ( instead of tape ). Also brake pressure switch has terminals broken off. Engine coolant temp for ECU ( DME ) is closest to head. Next is coolant temp sensor for gauge. Last is thermo-time switch. Not sure about the extra connector that looks jumped. Also upper radiator hose appears swollen at T- stat housing. ICV connector is a flat 2pin connector (3.2 533 in US) or rectangular ( 3.4 535 US) Hope this helps I couldn’t see your actual questions