Hot re-start issues: I'm out of ideas, what are yours?

[BRRV]

Assuming you're addressing me, on my car: fuel system was gone through completely, and I mean completely. Residual fuel pressure holds per test at pressure more than 30 minutes after the fact, I forget the original test value, but it passed once I replaced everything. The entire fuel system on my car was replaced, including a new BMW (VDO) in-tank pump, fuel filter, Bosch main pump, hoses, injectors, FPR, and removal/replacement of the 'dampers'.

(The problem does manifest itself both hot and cold ambient temps when at operating engine temperature; one small workaround I discovered [read it in a Bosch manual] is to 'part throttle' the pedal at hot restart; this seems to help a bit. Haven't tested that at 90F though.)

If not addressed to me, apologies, carry on.

[Mike W.]

To tn535i’s point, what does the residual fuel pressure look like? Should hold pressure and bleed down over 20-30 minutes.

I don't know what the spec is, but I've cut into fuel lines in junkyard cars that have obviously been sitting quite a while, months at least, and judging by the spray they had close to or full pressure. So to me it says a good system will hold pressure almost indefinitely.

[MattC]

Mine will crank and start easier after 6 hours then it does after sitting 1 hour. It'll also crank fine after sitting 1 week. I assume fuel pressure bleeding down would make it harder to start the longer it sits. Not so in my case.

The only common thread I can see so far is temperature. It cranks fine when the engine is either stone cold or hot. Anything in between and it struggles. I removed the inline resistor from the CTS wire last night but haven't had a chance to test (east coast snow storm ). Will report back any news this weekend.

[LeiseyJr]

I still have this issue and its uhh bugging me. If TB is leaking then, you should be able to spray brake clean or something on it should raise the idle. I too have replaced literally everything on this car fuel injection wise so I am upset its doing it. Maybe its a M1.0 feature

Untitled by samleisey, on Flickr

Crankcase vent is interesting point

[MattC]

Hey Rick,

FWIW, mine does this too. 1984 533i with a rebuilt M30B32 motor in it. Cold starts are strong but warm starts require multiple attempts. However, immediate hot restarts (sitting <5-10 min) seem fine - starts right up. It's when shut down a bit longer that I have the most trouble but can use full accelerator to slowly bring to life. New Coolant temp sensor, Thermotime switch is original, I believe CSV is original, O2 sensor probably not original but unsure how old.

I wonder... if coolant temp drops below TTS setpoint and actuates CSV, could problem be that ambient air temp (intake) is warm enough that CSV enrichment causes difficulty starting warm?

A couple years back I had the issue of a good cold start, but would not start warm until the engine fully cooled off. Turns out I accidentally broke the solder joint of the inline resistor located inside the Coolant Temp Sensor boot. Unfortunately, this is not the case today.

On a separate (maybe related?) note, mine seems pretty sluggish when driving in very hot weather. Need to rev a little higher in 1st, otherwise it acts like I'm starting up in 2nd gear.

-Matt

I believe my issue has been resolved.

Last weekend, I installed my newly refurbished stock fuel injectors (from Rich @ Cruzin Performance) and installed a brand new Genuine BMW Cold Start Valve purchased through ECS Tuning. Since then, I drove 150 miles over about 4 days (to/from work, and around town) with various shutdown times ranging from 30 minutes to 4 hours. In each "warm restart", the car started on the first key stroke without needing any throttle. Ambient temperatures 85-95F, which always exacerbated the issue in the past.

My theory is a leaking CSV that enriched the mixture enough to make a warm restart difficult, but would not affect a cold start (because it needs the extra fuel anyway).

I'll continue to track it, and will report back if anything changes.

[Mike W.]

I still have this issue and its uhh bugging me. If TB is leaking then, you should be able to spray brake clean or something on it should raise the idle. I too have replaced literally everything on this car fuel injection wise so I am upset its doing it. Maybe its a M1.0 feature

Crankcase vent is interesting point

Brake cleaner is non flammable so don't bother with it. However carb cleaner spray is flammable and will do what you're suggesting, or an unlit propane torch. But no, hard starts aren't a M1.0 feature. A worn butterfly bore won't do it either. I won't say I never had problems, because I did, but when it was right it fired after 6 compressions, or 2 revolutions under normal conditions, albeit perhaps a bit longer under very cold, by my standards, say under 30F. I even had 2 vacuum lines unplugged one time, passed smog and it ran fine except for a slightly higher idle, maybe 100 RPM or so. But it started fine. That was from 175k to 330K when I sold it, so it wasn't an overnight sampling. One time, somehow, the intake boot even came off at work one night. It did start a bit hard that night, but not terribly so. It did run like crap though.

My problems were almost always due to too much fuel, not too little. When I bought it the injectors leaked like a sieve. Cold starts were fine although you could smell some gas. A 2 minute hot start was fine, but say 10 or 15 minutes? That was a problem. Hard starting and it ran like crap for a minute or so. Experiment, spray some gas or carb cleaner in the intake and see what happens. If it's worse, then you have too much fuel already. Better? Then not enough.

[MattC]

My problems were almost always due to too much fuel, not too little. When I bought it the injectors leaked like a sieve. Cold starts were fine although you could smell some gas. A 2 minute hot start was fine, but say 10 or 15 minutes? That was a problem. Hard starting and it ran like crap for a minute or so. Experiment, spray some gas or carb cleaner in the intake and see what happens. If it's worse, then you have too much fuel already. Better? Then not enough.

This is exactly what I settled on too... Too much fuel.