DIAGNOSIS REQUESTED.

Hello everyone.

Situation:

2007 530i. Highway at 60MPH with cruise control. RPMs randomly shifted by approximately 100 - revving randomly between approximately 1800RPM and 2000RPM (like the ECU was 'searching'). I knew there was a problem. The highway was continuing onto a very low-slope bridge, and giving a little bit of throttle did not increase speed whatsoever. This was perhaps 20 seconds after the first problem. I pulled over onto the shoulder, perhaps 40 seconds after the first problem. The car was stumbling somewhat. I turned the car off. Then, I restarted, thinking "maybe it's just a random electrical problem and a restart will reset everything". However, the car died within 5 seconds of starting. I assumed this was a head gasket failure as it acted exactly that way. I only tried starting it twice and it died both times.

The tow truck towed the 530i home and I did a compression test on all cylinders. Every cylinder was normal except #6. I assumed this was a head gasket failure on 6 only, however, I was told to add a teaspoon of oil to that cylinder and run the compression test again. The compression returned to normal after the oil was added. I'm a great mechanic but not an expert! I assumed that this meant the rings are bad on cylinder 6. Is this true? I assumed that the oil added in the spark plug hole restores the compression to normal because the rings are bad precisely because the oil reseals the ring gap and if it were the head gasket then the compression would have remained low instead of returning to normal.

The car was easy to start and drive and reverse into a garage to work on it after being left by the tow truck. However, after running that compression test and reinstalling every spark plug and coil pack and wiring connection, the car has not been able to stay running whatsoever.

(1) noticed problem on highway.
(2) restarted car and it died.
(3) tow truck drops car off.
(4) car starts and backs into a garage.
(5) compression test and oil in cylinder test determining low compression on #6 and normal compression with oil added to the cylinder through the spark plug hole.
(6) all parts reinstalled.
(7) engine will start but will never remain idling.

Are the rings bad on this engine in only one cylinder, #6, or is there a chance this is a head gasket failure?

any information is certainly appreciated and suggestions are great for the cheapest way of repairing this car.

 

Read the BMW specific DTC codes and then post them here.

 

Thank you. I only have a Foxwell code scanner. There have never been any codes shown on it. I removed some oil from the oil pan drain plug yesterday and there was absolutely no sign of coolant in the oil. The head gasket went bad in October of 2023 and I replaced the head gasket in May of 2024... I'm very poor. I live in a travel trailer next to the train tracks and have never had a career job... I don't have money to spend. I was going to check the coolant expansion tank to see if there was any sign of oil in the coolant, however, as I just said, I replaced the head gasket because of it's failure just last spring and even with the drain and fill of the coolant (and proper bleeding of the coolant system) there was still gummed up oil/coolant in the expansion tank - so, that's an inconclusive test unless I absolutely flush the system perfectly then attempt to run the engine then see if there is oil in the coolant. So, because there was zero coolant in the oil from the oil pan, this leads me to believe that it must be the rings or valve stem seals that are bad on only that one cylinder. It wouldn't make sense for the head gasket to be leaking in only one cylinder and also to not mix coolant into the oil unless of course the oil was being pushed through the head gasket leak into the coolant chambers without any possibility of it going in reverse... which doesn't make sense but I could be wrong. I'm in a pretty bad spot right now and I'm certainly looking at the ideas of repairing this at all costs.

 

The code scanners I have access to have shown nothing… I have been hoping to get the codes read somewhere.

it is sure a sad situation… it was 50,000$ new, I bought it for 5000$, and I can’t let it sit inoperable at the trailer park rental property, so now it’s basically worth 500$!
obviously, I bought a $500 car to get to work, and, perhaps not as obviously, I certainly hope that I could get money soon to repair this.

It has to be the rings are bad on cylinder six, right? The compression test showed low compression on that cylinder, then I added a bit of oil to the spark plug hole and the compression became normal again… What else could it be besides the rings? The head gasket wouldn’t have made the compression return to normal and it couldn’t be a valve stem seal or even a valve stuck open. I guess I could open the engine, but we’re not allowed to work on vehicles at this property. any suggestions?

I’m definitely going to get the codes red any chance I get. And I would repair it instant if I had the money. But I have about 20 K of debt.

 

Man I'm going to be honest with you. Just get rid of it. There's too many variables and nothing positive. If you just so happen to get this fixed with no reader and not being able to work on your vehicle at its location you are going to have another issue following it. If you had the funds to do it I'd say keep going but you're going to dig yourself in a deeper whole

 

exactly. I agree. It is for sale and has been listed for perhaps two weeks now. If anything changes, who knows if some miracle happens that I can keep it… but at this point it’s only sensible for someone who is either making a full track car build or someone who is doing an engine conversion.