Strange behaviour - starting/running issues

Mon Apr 30, 2018 8:45 pm

Hey guys,

My M52 swapped 1991 E30 318i Lux struggles to start and run since a new (used) fuel tank was installed. I'll try to give as much explanation as possible so bear with!

Old tank was rusty so I bought another second-hand one to replace it. I didn't carry out the work (the guy who did was a bit of a clown who I've since fallen out with over other issues). Was some confusion over 55 vs 63L tank but I got a 63L one because whilst 318i didn't usually have them, I believe the Lux did.

Sruggles to start every time but never fails completely. The struggle is very consistent, almost exactly the same pattern each time.

Idle is a bit low and lumpy. Car feels quite smooth and punchy when driving but not 100%.

Fuel pressure at idle is 42psi which I believe is fine? When I turned the ignition on (not the engine) the pressure shot up to 40/50psi and then reduced back to 0 over the space of a few seconds. Is that normal or should it hold at 50psi with the ignition on?

Did a smoke test and found two vacuum leaks at the crankcase breather and ICV > intake hose. Replaced both. CCV was also SUPER blocked.

Thought the crankshaft position sensor was reading a low resistance so replaced that but it made no difference.

Doesn't matter if car is cold or hot - same thing each time.

Have also replaced fuel filter and fuel pump (used, sorry!) to no effect.

Any ideas? It's not an OBDII so I can't read the codes

Mon May 07, 2018 3:42 pm

Update:

Did a compression test today. Every cylinder read between 110 - 120psi. So very consistent but I believe quite low?

Will do another fuel pressure test tomorrow.

Wed May 09, 2018 12:35 am

i understand that the e30 fuel pump only runs when engine is cranking and obviously as engine is running.
once the car has been started and stopped it should hold fuel pressure for a long time with ignition off .
f it does not there is a problem , pressure leaking somewhere it should not be.
there are other posts on here explaining how to test various components in the line. with the aid of a gauge and clamps
especially from an expert named Brian on here, do a search.

bye the way no E30 is obd2. codes can be read but you need the correct equipment / obd1 reader.

how do you do a smoke test on the vacuum lines ?

Wed May 09, 2018 9:10 am

Thanks for the reply.

A fuel pressure leak is next on my list. Someone mentioned to clamp the fuel line going to the fuel rail when I turn it off so fuel can't drain back to the tank, and then seeing if it starts easily.

I did the smoke test by just pumping a disco smoke machine into the manifold via the brake booster opening.

Wed May 09, 2018 10:28 am

DON'T run the engine with the return pipe clamped off.
Connect a £15 fuel pressure gauge, then clamp the pipe immediately after stopping the engine, and watch what happens to the pressure.

Thu May 10, 2018 1:25 pm

Okay, where should I connect the gauge and where should I clamp? Previously I connected the gauge to the shrader valve on the rail.

In other news, I've given up and bought a replacement engine. Having said that, I'd still like to know if this is an engine issue or a fuel delivery issue as I don't wanna bolt the new engine in, only to have the same issue!

Thu May 10, 2018 3:59 pm

ACJJ619 wrote:Okay, where should I connect the gauge and where should I clamp? Previously I connected the gauge to the shrader valve on the rail.

In other news, I've given up and bought a replacement engine. Having said that, I'd still like to know if this is an engine issue or a fuel delivery issue as I don't wanna bolt the new engine in, only to have the same issue!

Hell !!! I really hope this turns out OK for you

Mart.

Thu May 10, 2018 7:34 pm

New symptom!

This afternoon on the way home from work my rev counter wasn't working correctly. I'm not sure if it's related or not but may help track down the issue?

It was refusing to go lower than 1,100rpm, and at low speeds it wasn't moving until I went above that as if there was a dead zone at the bottom of the gauge. Could this be related?

Mon Jun 04, 2018 9:02 am

I got bored trying to diagnose the issue so I stuck a different engine in.

The first 80 mile journey home was perfect! Since then though it's developed similar symptoms.

”¢ It starts fine (unlike before)
”¢ Running is now inconsistent. If I'm cruising along at 30/40mph it feels like I'm shaking the throttle pedal most of the time - lurching and jerking around. Sometimes it'll suddenly clear up and run fine for a bit but most of the time not.
”¢ Idle is quite lumpy most of the time but sometimes super quiet and smooth.
”¢ A lot of backfiring on deceleration (I have no cat or mid-box)

Have tried two fuel pumps and two MAFs to no avail. Tried doing another fuel pressure test but the kit broke.

Does this sound like the same issues as before? They're similar but not identical, and whilst it was quite driveable before because it was consistently a-bit-poor, it's now either perfect or dreadful so I'd argue it's less driveable.

The only thing I haven't changed is the TPS, ICV and O2 sensor?!

It's strange that it ran fine for the first long journey! Why would it just suddenly become poor?! I was expecting it to get better as the ECU learns and adjusts but alas...

Mon Jun 04, 2018 9:35 am

Your OP starts with a tale of a rusty fuel tank and it being changed by a 'clown'. There's also a mention of the fuel rail not maintaining pressure after the pump stops.
Since you have changed the engine and still have similar problems, it seems likely that the problem has its roots in the above.
Also, why have no electronic diagnostics been carried out? The Siemens ECU has excellent diagnostics potential, so get it scanned.

Is the TPS fitted definitely the correct one for a M52?

Mon Jun 04, 2018 10:51 am

Thanks for the reply.

I suspect so, however I'm just not sure what could be the issue back there. All I can think of is the chap accidentally pinched a fuel line between the top of the tank and the body? I plan on lowering the tank slightly this weekend so hopefully I can see then.

Because my diagnostic port doesn't work. The only solution I can think of is removing the ECU and sending it to EndaTuning to read the codes with the ECU out of the car, so that's what I'm going to do. It's not a perfect method as apparently it could add some other codes when he plugs it in, but he's hoping he can see how many times each code has been triggered which may help indicate what's wrong.

Yes it is, it's the one which came with the engine. Nothing has changed since the successful drive home.

Mon Jun 04, 2018 7:38 pm

Take the pump out of the tank there is a 1 way valve that is after the pump and connects to the hard line. Make sure you split the difference where it pushes on. You sound like your loosing pressure in certain conditions.
I had this on a 325i it would only ever start on 2nd turn of the key.
Also I'm sure you have done it but change fuel filter

Thu Jun 07, 2018 9:06 am

Okay I have the codes back from Enda.

Code - Description - Times seen - Countdown

He says a few of these were expected to trigger when he plugged the ECU in to get the codes so that would probably explain the ones on 1 - 40 (meaning it's triggered once and it was on the most recent engine cycle).

He said the initial surprise was seeing 4 cylinders trigger errors all at the same time. Possibly a loose plug?

There definitely seems to be an issue with the TPS and ICV however. The fuel pump relay too possibly?

Having said that, I would expect a lot of them to be on 39 as that would indicate they've thrown codes at every engine cycle except when Enda plugged it in. The fuel pump relay at 31 indicates it hasn't triggered a code for the past 9 engine cycles.