Just picked up an e30 last week...want to get it tuned up.

[bryant.cw]

I have searched, lurked, and read the bentley...but I can't diagnose engine running troubles.

Car has new cap, rotor, wires and plugs, timing belt and waterpump. I just replaced the coolant temp sensor, o2 sensor, fuel filter. Previous owner said he just had the valves adjusted, but one seems a little louder than the rest (then again, it could just be some other ticking sound in the engine) 112k miles.

Looking over the car, an '85 325e(s?) somewhere along the lines a previous owner put a dinan chip in it (which I removed to just get everything back to normal, and consequently broke) and also saw fit to adjust the co2 mix screw and afm dial leaving me know way of knowing where it was stock. I checked for vacuum leacks with carb fluid and didn't find any. Most everything under the hood looks pretty fresh, so i don't think there are any leaks.

Car runs rich, and the plugs ranged from a little too rich, to quite black. Rear diving board is stained black a little next to the exhaust, so its probably been going on a while.

Here are the symptoms of the car:

Hard to start cold or warm. Half the time when it starts it sounds like its running on anywhere from 5 to 3 cylinders, the rougher its running the sooner it just sputters out. The other half of the time it starts normally. This was noticeably improved with the new fuel filter, but not totally.

When its running normally, about half the time it bounces back and forth between 500-1000rpm, and spends the other half of the time idling at about 900rpm.

There are large dead spots of power, and sometimes when you hit the gas, it seems to take a full second or so for it to get up and go. These vary minute to minute where they are, although 2000rpm seems to be about the worst.

Fuel cutoff seems to happen at an indicated 4000rpm instead of up at redline.

Seems to run better with o2 unplugged.

Tested the FPR by pulling a vacuum on the line leading from it to the manifold and it changed the RPM and didn't seem to leak the vacuum out.

Main fuel pump doesn't come on with the ignition in the "on" position, only until you start the car, is that right? It also buzzes all the time, but its always supposed to make some noise, right?

It sounds maybe like low fuel pressure, but I don't feel like making a mess and getting new fuel hose and clamps or buying a fuel pressure gauge only to not know what I'm looking at. Reading Bentley would make it seem that I have to run about 30 tests to find the fault(s).

I've made an appt. for next week to have it checked/fixed professionally, but am hoping with some guided advice I can avoid the $85/hr shop charge.

Any simple stuff I can check for with simple tools? I don't have the advanced test equipment other than a decent multimeter.

Note: I am in Denver, a mile above sea level. Don't know how well motronic 1.1 and the sensors its equipped with can deal with that.

[E30_fiend]

well first off, if your car runs better with the O2 unplugged, replace it. Its probably the stock sensor anyway.

you said :

It sounds maybe like low fuel pressure, but I don't feel like making a mess and getting new fuel hose and clamps or buying a fuel pressure gauge only to not know what I'm looking at. Reading Bentley would make it seem that I have to run about 30 tests to find the fault(s).

but before you said you think its running rich. If you want to avoid a lot of labor time at a shop, take care of the little easy things that could be effecting you motor.

Get a new fuel pressure regulator

replace the inlet and return fuel lines from the firewall to the fuel rail.'

replace your O2 sensor

and if you can, find someone with an ETA and swap the AFM into yours and see if that fixes anything.


but most of all, change your O2 sensor.


let us know what happens.




Taylor

[jlevie]

You could have a bad cold start valve or excessive fuel pressure (bad FPR), either of which will cause a rich condition.. A fuel pressure check will quickly tell if that's a possibility. The Bentley does have a good write up on checking the fuel system and the fittings and gauge you'd need to purchase will be well less than one hour of shop time. To check the cold start valve, pull it from the intake and jumper pins 30 & 87 in the fuel pump relay socket to run the pumps. If fuel leaks from the valve it needs to be replaced. I think this car also has a sensor for the cold start valve, which could be bad.

The fuel pumps only run when the DME sees timing information from a rotating engine, so that observation is normal. A very mild buzz from the high pressure pump, audible from outside of the car, is normal. But you should not be able to hear the pump above idle or while driving. A pump that noisy is either worn or having to work too hard. The latter can be the result of a bad FPR or blocked supply/return line, (in this car) a bad transfer pump, or a build up of rust in the tank that clogs inlet screens and/or the filter. To check for rust in the tank (pretty likely on an E30), pull the transfer pump and sender and use a stick to stir the bottom of the tank. If it feels like there's a layer of sand in the tank you'll need to replace the tank or acid clean and seal the tank.

Returning the AFM mix screw to correct settings requires the services of an exhaust gas. analyzer. Without access to a flow bench I don't know a way to reset the vane dial. It probably would make more sense to simply buy a good used AFM. And given the other symptoms, there's a good change that wear in the vane potentiometer is present making a replacement AFM more attractive.

The bouncing idle is probably the result of a sticky ICV or a bad ICM. You can try cleaning the ICV, but if the ICM is the cause it will have to be replaced. But before replacing the ICM (or ICV) you need to verify correct operation and adjustment of the TPS (see the Bentley). If it isn't reliably indicating idle position of the throttle body the idle will vary.

Which coolant temp sensor did you replace? There are two. One is used for the temp gauge and the other supplies data to the DME. The one that matters as far as engine operation is concerned is the one that supplies data to the DME.

[jmc1590]

Check for vacuum leaks. Start the engine and remove the oil dipstick. If the engine begins to bog down severely, then your vacuum lines are probably in good shape. If no change in the idle speed or sound of the engine, start looking for vacuum leaks. (There are many write ups on this, search for vacuum leak checks. )

900 rpm idle seems a bit high. Check your cold start temp switch as well. (Yellow top, on thermostat housing, with two leads.) Until the engine warms up, it should provide no continuity. With the engine warm (past 45* C, or 113* F) it should allow current to past through. To test, carefully remove the leads and jumper with a small piece of wire. If your rpms drop to around 700 or so, that could be the culprit.

The fuel cutoff could be related to a failing pump or FPR. It's not real difficult to do the FPR tests. (Parts & tools shouldn't set you back more than $40.) Just build a "T" with a small piece of fuel line on one side, with the fuel pressure gauge attached in the middle. Disconnect the fuel line at the cold start injector, plug it into your "T" and put the new small piece on the injector. Clamp everything down, and start the engine. If everything is working right, you should have 33-34 psi (minimum) on the gauge. If not, suspect the FPR. Next disconnect the FPR vacuum line. Your pressure should rise to around 45-50 (or more!). If not, look at replacing the fuel pump. That will definately help you narrow down the problem.

If I'm not mistaken, an '85 'e' is a standard eta, not a super eta. That would mean that you have a Motronic 1.0 basic, not a 1.1 adaptive.

Let us know how this progresses...

[bryant.cw]

With regards to the motronic, its not a super eta, and has the dumb motronic brain.

I replaced the new-ish looking o2 sensor with a new bosch unit and it didn't help. Still seems to run better with it unplugged.

I checked for vacuum leaks under there pretty thoroughly and didn't find any. It responded to taking the taking the oil cap and dipstick out.

I replaced the sensor that feeds the DME. The old one looked pretty rough.

This is great advice, I will try it out today.

[bryant.cw]

Also, I'll add some pics.

[bryant.cw]

Well, checked the fuel pressure just like you said at the cold start injector (which I also checked while I was in there and was fine) and it was right at about 30psi going to 35psi when I took the vacuum off the FPR. Looks like I need a new pump!

This has been such great help. Bentley just made the whole process seem so complicated. I'm gonna do that this afternoon.