Advice needed; injectors or fuel pump check valve?

[Red Z4]

I recently purchased a 2003 BMW Z4 with the 2.5 liter engine and it has 150,000 miles on it. I've noticed a problem with hot starts. The cold starts are fine it's just the hot starts. It takes a little longer to crank and get going and it idles rough afterwards for a few seconds. I hooked up my fuel pressure gauge and put the key in the ignition to the on position and the fuel pressure goes up to 50 psig. It slowly bleeds off pressure over the course of a few minutes and then hovers around 10 psig. My question is are the injectors leaking or is the check valve leaking? I would assume it would be the injectors because of the rough idle situation that goes away after a few seconds but I wanted some advice on others that have more experience with BMW's than I do

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Oh I forgot to mention a really important detail. When it's idling rough in the hot start condition I smell raw fuel really strongly. I assume that this was coming out the tailpipe because the injectors were leaking by and the engine was clearing the gas that was leaking but I'm not sure

[dworthy]

Welcome to the Forum!

The best way to find a leaky injector is to look at LTFT/STFT values using INPA or ISIT software. You can also use a Foxwell scanner IIRC to do the same thing.

Your pressure is correct, and the bleed-off shouldn't be occurring as much so it can be a check valve.

The biggest thing I see with bad idle for hot start/restarts is vacuum leaks. Being that your car is 15 years old, a lot of the rubber intake tubing will be bad, so start with a smoke test. BTW is your check engine light on?

[ross1]

I recently purchased a 2003 BMW Z4 with the 2.5 liter engine and it has 150,000 miles on it. I've noticed a problem with hot starts. The cold starts are fine it's just the hot starts. It takes a little longer to crank and get going and it idles rough afterwards for a few seconds. I hooked up my fuel pressure gauge and put the key in the ignition to the on position and the fuel pressure goes up to 50 psig. It slowly bleeds off pressure over the course of a few minutes and then hovers around 10 psig. My question is are the injectors leaking or is the check valve leaking? I would assume it would be the injectors because of the rough idle situation that goes away after a few seconds but I wanted some advice on others that have more experience with BMW's than I do

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Oh I forgot to mention a really important detail. When it's idling rough in the hot start condition I smell raw fuel really strongly. I assume that this was coming out the tailpipe because the injectors were leaking by and the engine was clearing the gas that was leaking but I'm not sure

your combined symptoms tell me that some or all of your injectors are leaking down after shut down. Some of the leaked fuel will evaporate or run past the rings given enough time(cold start) also, the engine wants more fuel when cold so this over rich condition will be less noticeable.
Does the oil smell like fuel? Leaking injectors will dilute the oil and fuel washed cylinders on cold start see accelerated wear.
Plenty of places to "rebuild" your injectors, many offer exchange service too.
I my have a set of appropriate cores if you can't find an exchange service and don't want the vehicle down while the service is done.

[Red Z4]

The weird thing is that when it was misfiring and idling rough that the EML light but when I went to plug in my OBD reader to catch it nothing was registered

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Oh and I had some throttle body cleaner that I was spraying around every hose and opening to see if a change in idle speed was detected and there was no change in idle speed so I assume there was no vacuum leaks. Also it only happens on hot starts and cold starts are good so I would assume a vacuum leak to be present in both situations?

[shadowpuck]

a scan with a bmw scanner would be helpful - as would a smoke test, best testing for vacuum leaks involves a smoke test.

[dworthy]

Using throttle body cleaner to find leaks don't work. They only find Gross leaks, not small ones. Also if you have 5 small leaks, that can equal 1 Gross leak, so find a shop with a smoke test machine.

[MarcoZandrini]

Go to www.bimrs.org to find a reputable indie shop that specializes in bimmers in your area.

[bmwdirtracer]

+1. OBD codes are useless, at best, and trying to use flammables to find intake leaks went away with carbureted engines/ You need a smoke test with a professional smoke machine, and a scan with a BMW specific scan tool.

[Red Z4]

I pulled the injector Rail and pressurized the injectors and did find two of them leaking. I ordered a new set of remanufactured injectors and installed them. One of them leaked worse than my original injectors! I'm working on getting them returned

[dworthy]

Slow down a minute, for it would be better to have them sent off to be cleaned. As you are getting 2 new injectors, it will make the motor unbalanced.

This is the best bang for your buck: https://www.rcfuelinjection.com/

I had a set cleaned and balanced by them, as well as several other forum member.

[bmwdirtracer]

+1 to RC Injection! This is the best bargain in the automotive world...for $25 per injector, you'll have full before and after reports, and the most perfect injectors possible. If you scratch the cylinder numbers into the injectors before sending them to RC, you will also know exactly which cylinders were likely having problems.

That said: personally, I don't think this is the actual problem. Yes, you should absolutely have the injectors ultrasonically clean and rebuilt and tested at RCI.

But I'm betting that you have an intake leak, and/or a temperature sensor failure. If the engine coolant temp or the intake air temp is grossly incorrect, this would give your trouble.

Connect the car to a good BMW diagnostic scan tool, so you can look at not only the BMW codes, but also the live data for temp sensors and MAF. A smoke test is certainly called for, and servicing the injectors at RCI is a very fine idea!

[ross1]

+1 to RC Injection! This is the best bargain in the automotive world...for $25 per injector, you'll have full before and after reports, and the most perfect injectors possible. If you scratch the cylinder numbers into the injectors before sending them to RC, you will also know exactly which cylinders were likely having problems.

That said: personally, I don't think this is the actual problem. Yes, you should absolutely have the injectors ultrasonically clean and rebuilt and tested at RCI.

But I'm betting that you have an intake leak, and/or a temperature sensor failure. If the engine coolant temp or the intake air temp is grossly incorrect, this would give your trouble.

Connect the car to a good BMW diagnostic scan tool, so you can look at not only the BMW codes, but also the live data for temp sensors and MAF. A smoke test is certainly called for, and servicing the injectors at RCI is a very fine idea!

Did you notice in the original post that fuel pressure is bleeding of rapidly?

[bmwdirtracer]

Yes, I did see that. I have seen dozens of BMWs that lose fuel pressure shortly after shut down, but they run perfectly, and start within one second.

I also saw that the OP smells raw fuel...and hasn't mentioned black smoke. Perhaps a small fuel system leak at the fuel filter?

And, this only happens on a hot start, which leads me to think of the temp sensor or an intake leak.

I'd do a smoke test, look for fuel drip residue underneath, and watch live data for ECT and IAT.

As I said, sending the injectors off to RCI is a wonderful idea -- I've always been very happy with seeing the differences between before and after reports -- usually ~15% difference in the "before", and less than 1/2% difference in the "after".

Absolutely, smelling the dipstick is wise...I usually try to light it on fire, too.