No Power when Engine is cold - 525i

E28 technical advice asked and given! Troubleshooting, modifications and more.
Post Reply
Magava
Posts: 15
Joined: Jan 07, 2018 7:17 AM
Location: Nairobi

No Power when Engine is cold - 525i

Post by Magava »

Hello all,

I have a 1986 525i with an M30 Jetronic.

My issue is that when the engine is cold the car just wont go. Even if you floor the accelerator it will not get past 40 km/h and revs wont go past 3K. As the engine heats up it keeps improving and once its at operating temperature the car is a rocket.

I've lived with it like that so far as once the car is warm its fine but its annoying when you first get going and you are backing up traffic so people think its coz you are driving an old pile of junk, not knowing its actually a beast :laugh: I have replaced the TPS, bought new spark plug wires, serviced the injectors, refurbished the MAF, still no change. I live in a tropical climate so the problem is not the ambient temperature.

Any help would be greatly appreciated.
Ju@n
Posts: 702
Joined: Apr 27, 2013 1:11 PM
Location: Uruguay

Re: No Power when Engine is cold - 525i

Post by Ju@n »

Does it feel like an ignition misfire? (so as a rev limiter)
Or is it a smooth loss in power?

First one would point to something related to either the ignition module or the temperature sensor for it (you'll have to bear with me, since I'm not familiar with Jetronic in BMW, only Mercedes)
Second one would indicate the temperature sender for the ECU (if it is KE-Jetronic) or the WUR (if it is K-Jetronic)

Edit: Disregard, just saw that the 525i came with L-Jetronic, not K(E)-Jetronic.
Look at the temperature sensors
darbyhood
Posts: 92
Joined: Dec 23, 2015 1:21 PM
Location: Canada

Re: No Power when Engine is cold - 525i

Post by darbyhood »

I would suggest taking a look at your cold start valve if you have one, I’m not sure about the 525i but the 528e does have one. This is just a little solenoid that squirts extra fuel into your intake manifold as the car needs to run richer when cold. Cheers.
Mike W.
Posts: 26872
Joined: Feb 12, 2006 12:00 PM
Location: California Whine Country

Re: No Power when Engine is cold - 525i

Post by Mike W. »

darbyhood wrote: Sep 06, 2021 12:55 PM I would suggest taking a look at your cold start valve if you have one, I’m not sure about the 525i but the 528e does have one. This is just a little solenoid that squirts extra fuel into your intake manifold as the car needs to run richer when cold. Cheers.
No, the cold start valve is a cold start device, not a warm up device. At most it only works when cranking.
Aldo525
Posts: 276
Joined: Mar 24, 2021 3:04 PM
Location: CHILE

Re: No Power when Engine is cold - 525i

Post by Aldo525 »

Hi,

I have a 87' 525i e28 with auto gearbox. Similar issues when I bought it and today runs fine. Check:

- Temperture sensor (L- Jetronic), white sensor (or blue if replaced before). Not the temp gauge sensor
- ICV idle control valve. Could be closed all the time, giving not enough air when the engine is cold
- Fuel pump. Mine has two: one inside the fuel tank, other underneat the car.
- Fuel pressure regulator on the injection rail
- Vaccum lines to distributor
- Ignition timing point (22 degrees at 1850 rpm) VERY important

Seems you already change the spark plugs, if not, use NGK ZGR5A
Mike W.
Posts: 26872
Joined: Feb 12, 2006 12:00 PM
Location: California Whine Country

Re: No Power when Engine is cold - 525i

Post by Mike W. »

Aldo525 wrote: Sep 14, 2021 2:06 PM Hi,

I have a 87' 525i e28 with auto gearbox. Similar issues when I bought it and today runs fine. Check:

- Temperture sensor (L- Jetronic), white sensor (or blue if replaced before). Not the temp gauge sensor

- ICV idle control valve. Could be closed all the time, giving not enough air when the engine is cold
- Fuel pump. Mine has two: one inside the fuel tank, other underneat the car.
- Fuel pressure regulator on the injection rail
- Vaccum lines to distributor
- Ignition timing point (22 degrees at 1850 rpm) VERY important

Seems you already change the spark plugs, if not, use NGK ZGR5A
Good points, especially the bolded ones. I'm so used to Motronic controlling timing on US E28s I forgot about the conventional distributor and timing.
Aldo525
Posts: 276
Joined: Mar 24, 2021 3:04 PM
Location: CHILE

Re: No Power when Engine is cold - 525i

Post by Aldo525 »

Yes, ignition timing is key in those engines pre-Motronic but is not easy to see it the point trought the small window on the bell housing.

Another thing to check: Valve clearence 0,30 mm (0.012") intake and exhaust. Yesterday I check mine and the difference is noticiable.

Greetings
Post Reply