Phil 9xx

I have an S4 that has varying degrees of warm start difficulty. Today when I was going out in the car again for a ride (three hours since the first drive today) it was being difficult starting, so I pushed the accelerator to the floor (like I've done in the past on occasion) to get it to pop off and a little slow to lift my foot the car starts up and the needle swings to redline and back down on startup. I almost had a heart attack. I let the car idle for a few minutes and decided not to drive it.

The question is, was this event harmful to the engine (theoretically speaking)? Obviously, didn't blow the engine, but are there things I should look for, listen for over the next few weeks? Coolant in my oil?

I've done some troubleshooting, and think it's the fuel check valve that isn't holding pressure in the line. After an hour the pressure drops to zero.

Thanks for any feedback (mostly to settle me down)!

Randy V

Don't be a granny.

It's a Porsche 928!

Alan will explain it for you.

Alan

It is designed to run at redline under load for periods of time - so a brief blip warm is unlikely to be any issue - unless there are underlying other issues...

I wouldn't worry about that - however sounds like you do have an issue you need to fix affecting the warm start...

Alan

76FJ55

Unlikely to cause any harm. You shouldn't have been able to over rev it as the rev-limiter will catch it before you can. The ony real issue with high rpm after start up, is lack of oiling. But assuming the oils is still warm and flowing as designed, and the fact that you'd been cranking it for a while trying to start it before flooring it, I would guess you should have had oil flow to the bearings before the trip to redline.

Phil 9xx

Good to hear! Regarding the 'granny' comment...It is my baby, you know! Thanks.

17prospective buyer

I know how you feel about it being your baby. Well, i think we all know how you feel! It shouldn't be an issue unless there are pre-existing motor issues like high oil pressure (restricted oil gallery, clogged filter), or you live in Canada where -20 cold starts are not uncommon (unless it's a winter like this where it's been relatively mild (1.6C average winter temp)) and you're running 10W30 or higher organic motor oil that is virtually congealed at those temps.

Sounds like you're spot on with the hot start issue. Either that or your fuel pump's bushings have failed and do not hold pressure.

Bill Ball

More likely your warm/hot re-start problem is from leaky injector(s) than a check valve. It only takes a few seconds to build pressure with the latter and then it should start normally, maybe with a little stumble for a few more seconds until all the injectors spray evenly. Holding the throttle wide open would make no difference as that has nothing to do with building fuel pressure. With leaky injectors flooding a few cylinders, you can help resolve the flooding by holding the throttle wide open, as you did, bringing in a lot more air. Classic leaky injector symptoms are the car starts perfectly if left sitting overnight or at least several hours (i.e., a cold start). It also starts OK hot IF you stop and IMMEDIATELY restart, but it becomes very hard to start if you let it sit 10 minutes to an hour or so, which allows time for the leaky injector(s) to flood the cylinder. What is your symptom pattern?

Phil 9xx

Bill,
Thanks for the response. You've described the symptoms exactly as I've experienced with my car. I defaulted to the check valve because the injectors were cleaned/tested a year ago and they 'passed' the leak down tests (see attached). Fuel pump was replaced last fall, but not the check valve. The FPR and Dampners are original. Can't detect the smell of gas in the vac lines of the two that are easily accessible. Do you still think it's the injectors?? Thanks.

danglerb

If opening the throttle helps to start, sounds like it might have too much enrichment so maybe temp sensor?

Bill Ball

danglerb brings up a good possibility, especially since the injectors were serviced. Temp II sensor. It's on the right side of the water bridge. Pull off the plug and test each pin versus ground for resistance. It should fall from 4-6.8K Ohm range when the engine is cold to 250-210 Ohm range when warm. If the resistance is still high when hot or infinite (broken) at any time then that would cause hard starting when warm/hot. BUT it would also affect the way the car runs when warm AND it would make the car hard to start on instant re-start as well as somewhat delayed restart. If your restart problems are after the car sits for several minutes and not on instant restarts, it's not Temp II, but test it anyway.

How does the fuel pressure look over 30 minutes?

Phil 9xx

I replaced Temp II last year. Top end refresh, which included typical sensors (knock, hall, CPS, etc). New O2 sensor since I'm listing recently replaced parts. Cleaned but original MAF (helped drop the idle 100 rpm). Pressure after 30 mins is 34 psi. Takes about 75 mins to drop to zero psi.

76FJ55

Could also be a leaky diaphragm on the fuel pressure regulator or fuel pressure damper.

Shark_Week

regardless of when you last replaced components, or how old they are, they could still be faulty. trust me

Bill Ball

Your pressure drop is not within spec. It could be a number of leak locations, but if the symptoms are very hard starting after sitting for 10 minutes or so, leaky injectors with flooding is more likely.

MarkRobinson

Since there was no load nor enough time for heat to build because there was no load nor extended period of time there, you're probably fine.

My best friend got behind the wheel of my brand new '95 M3 (back in '95), and with 80 miles on the odo on a cold engine, pulled out on the road & was enjoying the song of the smooth revving 6-cyl, unaware that he was surpassing 7k rpm: we both yelled "AAHHHHHH!" at the same time. I could have killed him, yet, 50k miles later, motor was still solid & smoke free.