Not another rough start/idle/running thread... tried most everything so far

[BoxE30]

Hey guys, waited until I'd pretty much exhausted all of the usual things on the checklist. 1991 318is/M42 motor/stock everything

Cleaned idle control valve twice (and even replaced with new Bapmic unit from Amazon)
Replaced fuel filter (old one had a decent amount of soot)
Replaced fuel pump (TRE 340/255lph unit)
Replaced spark plugs (NGK BKR6EK)
Converted to coil-on-plug ignition
Replaced air filter (K&N filter)
Replaced DME, fuel pump and O2 relays (next to firewall)
Smoke tested vacuum system ($120 kit from Amazon) 10-15psi for about 10min
Volume tested fuel pump (right on at 255lph routed out of filter
Installed fuel pressure gauge on fuel feed line (consistently around 35-36psi and increases a bit with revs)

So today, I got a new fuel pressure regulator delivery (why not at this point?) and before install, I decided to try jumping the relay with the vacuum line pulled. Pressure read 41-42psi on the nose and I heard a faint sound in engine bay like air/gas squeezing by a tight seal. I mean, very faint, and then stopped. Then I noticed a pool of gas under the tank, which is a first after all these things I've done over approximately 2.5mos.

I then dumped the fuel in the filter just to ensure something hadn't been sucked into it. Looked clear/fine. Buttoned everything up and let the gas dry up on the underside of the tank. Car started and ran in the usual rough sort of way and had to keep on the revs (about 2k rpm) and backed it out of the garage and parked on the street, noticing a trail of gas in the 3-point fashion I parked.


Questions I have at this time:
1. Could a very small leak from the tank have possibly been the culprit this entire time, and would it really make the engine start and run so rough?
2. Was I wrong to jump the relay to check the fuel pressure in this fashion?
3. Leak from tank is on the passenger side. Probably about 3-4 gallons in tank right now. What could that be?
4. In case I need to replace the tank at this point (oh man, I really don't want to), what's everyone recommend for a reasonably-priced new aftermarket option?


Thanks in advance. This forum has really been a godsend for me with this car so far. I really need to jump on and contribute more as I learn more about these cars!

Sean

[82eye]

not sure the leak and hesitation are related. i'm not much help, but would solve for leak first. then fix hesitation with no worry of random kaboom.

[BoxE30]

not sure the leak and hesitation are related. i'm not much help, but would solve for leak first. then fix hesitation with no worry of random kaboom.

Agreed! Think I’m headed to the shop finally. I’ll update what I find out, but open to any tips before then.

[82eye]

Agreed! Think I’m headed to the shop finally. I’ll update what I find out, but open to any tips before then.

check external pump and lines to and from the pump. it's located near the passenger rear tire. it's likely something in there.

[ahlem]

Did you verify the wire connection on the passenger side of the firewall is unplugged? It’s accessible from the engine bay and a single wire connection. It needs to be unplugged.

[BoxE30]

check external pump and lines to and from the pump. it's located near the passenger rear tire. it's likely something in there.

Just one internal pump on the ‘91 318is

[BoxE30]

Did you verify the wire connection on the passenger side of the firewall is unplugged? It’s accessible from the engine bay and a single wire connection. It needs to be unplugged.

Still wondering what the heck that plug/wire is for but has definitely been unplugged since I’ve owned it. Good tip though

[Gregs///M]

The gas leak should definitely be repaired before continuing. Then I'd start by verifying your TPS sensor is adjusted correctly, ensure your engine harness is not corroded and verify your AFM is still good by using a scope at the DME. If your AFM is still the original unit, and not rebuilt, I would consider it bad.

[BoxE30]

The gas leak should definitely be repaired before continuing. Then I'd start by verifying your TPS sensor is adjusted correctly, ensure your engine harness is not corroded and verify your AFM is still good by using a scope at the DME. If your AFM is still the original unit, and not rebuilt, I would consider it bad.

Taking it in finally tomorrow. I can definitely raise this to their attention - thank you!!

[BoxE30]

Wanted to provide a quick update. Ended up being a faulty injector and a misfire. Upgraded to mustang injectors and it’s good to go.

[82eye]

Wanted to provide a quick update. Ended up being a faulty injector and a misfire. Upgraded to mustang injectors and it’s good to go.

excellent catch.
which ones are you running ?

[BoxE30]

excellent catch.
which ones are you running ?

Not sure of exact ones. The mechanic is a BMW fanatic with a 318is that's pretty done up. Mentioned having a set on hand and I figured while he was in there, may as well upgrade.

[OSAH racing]

I am chasing a rough idle that stalls sometimes. What ended up being the problem with yours and how was it fixed?

[82eye]

I am chasing a rough idle that stalls sometimes. What ended up being the problem with yours and how was it fixed?

the answer is two posts above yours.

[OSAH racing]

thanks