chasles22

hey folks,

had a little issue this morning that appears to be cleared up, i'd like a little advice/make me feel better.... here comes the wall of text:



back story. the ONE thing my 88' 928 $4 has going for it is that it starts immediately hot or cold 100% and idles/runs beautifully.

since September (when i moved from canada where she was born to tampa florida in case climate matters) i drive her at most a few minutes or max of an hour a week and in some weeks not at all. i should point out that in canada the gas i used never had ethanol but down here only 1 out of 4 or 5 top offs is ethanol free (in case water vapor etc matters)

a few weeks back i fixed a nagging issue (simple fuel gauge reading) by replacing the sender in the tank.

drove the car last week, she ran great as usual. got in her today and on the very first crank she turns over fine and strong, starts for maybe a few cylinders worth (literally a 1/2 second) and then dies hard right on the first try. i've never had a single issue like this so i try a few times and ultimately coax her to life by lightly pumping the gas pedal during the wheezing. at this point i notice (apparently due to my new found trust in the needle) that i let her get down pretty low (not empty, but in 3 years of ownership she's never seen less than half a tank). once started she ran fine, idled fine so i said "let's go fill up the tank", she took just under 16 gallons. on the way there (about a 4 minute drive) she ran fine under normal or soft acceleration and idle but under moderate to medium hard acceleration (nothing serious just some "clear out the cobwebs thinking") she almost dumped and coughed and wheezed until the revs dropped below maybe 2500 and then came back to life and again ran/idled fine. i stopped her at the pump, filled and then attempting to start/drive home PRECISE same symptoms.... one extra thought, revving her high to 4500-5000k in neutral on the way home ZERO issues, put it in gear and accelerate hard and cough wheeze cough! which i found especially weird.

so i put together the following thoughts:
1. out of gas (probably not - she ran well enough to get her to the station) and symptoms didn't clear with the fill.
2. fuel filter. surely a little sand/**** got into the tank when i changed the nearly 30 year old sending unit despite my best efforts. so then, oops i let the tank get down to E and then after sitting for a week problem appears out of nowhere. on top of that the PO was a POS who did expensive things (thankfully) like change the timing belt on schedule but NOT things like air (or presumably) fuel filters. ever.
3. fuel pump. both pump and filter thinking are related to "a little pedal pumping got her going but under power she coughs out"


SO here i come all worried but fine, i'll hit you guys up for some confirmation and head to the local napa who stocks bosch and mahle for her and grab a filter (my #1 candidate) and pump (because, why not while I'm in there)

i cant really find any useful posts about this when searching prior to posting (like a good forum user) and they all seem to relate to rough IDLE , not my problem. then i find some advice to the effect of "hold down the pedal and turn over for 10 seconds, due this 3x" and it will (apparently) either clear out the engine of a flood, or some other mystery thing.


so what the hell, i go try it. goddamnit she fires up like a beast about 3 seconds in and runs fine. damn. i shut her down and start her up again boom, totally typical start, crank, 1 second and good strong start like every other in the last 3 years. i run her up and down the street romping hard and no loss of power or failures.

so, if you've gotten through the wall of text here are the questions:

1. what the hell does the floor the pedal for 10 seconds thing do? is that apocryphal or legit?
2. what should i do now? change fuel filter anyway? take a highway cruise? replace some other much more expensive and difficult doodad? crack a beer?


thanks for the help and any suggestions. double thanks for actually getting through this post!

-charles

chasles22

One extra thought: several people have remarked (based on exhaust smell) that she runs rich but it's been that way since I bought her. Fuel related so I thought I'd add it in...

Wisconsin Joe

"Flooring the pedal" dumps massive quantities of air into the engine. If you are flooded, that will help clear it out. It's legit. I thought it was part of the owner's manual, but I can't find it in mine (86 ROW book).

If it's running well now, I'd be tempted to just keep a close eye on it. If it's a real problem, it will come back.

The one issue with ethanol gas is that it will absorb water over time. That's actually nice in colder climates because it takes the water out of the system without having to use "Heet" or similar.
It can cause issues if the car sits for a long time in humid conditions.

SteveG

How old would you say the oldest gas remaining in the tank is? Sounds like it needs to be driven to get all the stale gas out, maybe put some 1/2 bottle Techron or Seafoam in first. Ideally, drain tank, and re-fill use entire bottle of additive. Over winter, I put Stabil in.

Check TempII sensor first. Probably not the cause, but it is simple to do and easy to access.

Then

1. change fuel filter, if that doesn't clear it
2. check fuel pump is providing the flow rate minimums

Does it have original fuel lines?

chasles22

The oldest gas was the bottom of the tank, probably 4-5 weeks old. Its got an absolutely full tank (took 16 gallons) of shell. I opted for that instead of my local no ethanol provider in case bad gas was i figured the shell detergents might be good. It's been starting fine for 2 days near as I can tell. I'm going to check the tempII sensor and replace at least the fuel filer (if not the pump as well) and call it 100k mile maintenance. As for the fuel lines I've never looked but this car was a daily driver until I bought it and not a garage queen or loving project so I'm going to say fuel lines are original.

Magnus Rostadmo

I do not have any solution to this problem, and hope i do not hi-jack the thread.
I expirience some of this behaviour on my -87 S4. When i bought her and were starting up the very first time i was barely twisting the key and WOW that engine were firing easily ! Never ever started any engine so easily before. First piston on top and "Bang-fire" and settling to fast idle so smooooothly. Winter temp at about minus 17 degrees Celcius. I thought, me likey...a lot :-)

Since then back in 2012 i have expirienced that she does fire this easily not nearly every time, more like "occasionally" whatever outside temp and engine temp... but mostly not.
Have to crank some 3-4-5 revs before she starts.
A while after i bought her she developed a misfire at WOT and at revs over 3500.
I have been able to cure that replacing in this particular order both a tired/howling fuelpump & filter, coil-leads, coils, distributor caps & rotors and ignition wires. Got about 165`kms on her now and MAF were also replaced about 7 years and approx 35`kms ago. All ground Points cleaned.

But still she won`t fire easily more than 1 out of 10 times. All other seems fine with steady idle, no excessive fuel-consumtion or something like that. Pulls hard and strong.
When looking on videos from "Shark-meetings" it seems that many engines have this somewhat "slow-to-start" problem cranking for about 3-4 sec before it fires up.

What do you think Gentlemen...Temp sensor II ? Other things that might be wrong...and need to be replaced ?

Mrmerlin

Magnus I would suggest,

first deoxit the CE panel,
get the MAF rebuilt ,
replace the O2 sensor,
do an intake refresh,
NOTE do this if the sensors are original,
2 knock, 1 CPS ,1 Hall , 1 ISV.

Replace the fuel injectors. your choice on type original or 4 hole

Replace the 2 dampers and the fuel pressure regulator if these are original.

Replace the fuel lines.

Replace the connector to the temp 2 sensor and the sensor.

New spark plugs and air filter

Wisconsin Joe

If the fuel lines under the hood are original, they should really be replaced.
They are 27 years old. And they live in a "not too friendly" environment under the hood.

If they let go, you get to participate in a "Car-B-Que" (and you really don't want that).

The good ones aren't cheap, but the cost of the alternative is a lot more.

Magnus Rostadmo

Mrmerlin !
Thanks for Your suggestions. I will try it out as soon as i got time.
I do not have CAT so no O2-sensor then.

My English is not that good so if You could "decode" some of those abbreviations for me ?

CPS - Crank Position Sensor ?
ISV - Idle Stabilizer Valve ?
Hallsensor - ?

outbackgeorgia

After fixing all of the above and still no difference, replace/rebuild the LH computer. Or, replace it first and save a lot of work.
The hybrid chip inside will fail, so rebuild it now or later. This is a well known issue.

outbackgeorgia

Just to follow up, contact Louie Ott:
www.jdsporsche.com
Home of the SharkTuner
Rebuilt LH, EZK ECUs & MAFs available from agents worldwide.
USA agent for LH and MAF checking and repair is Louie Ott :-
http://www.performance928.com

Magnus Rostadmo

Thanks to you ourbackgeorgia !

I will absolutely consider a rebuild of the LH-ECU first as i understand they are well known to fail sooner or later.
I just did not know that they are prone to produce "hard starts" as well as "no-start". Thought they were mostly "Go or No-Go"

Mrmerlins suggestion about rebuilding the MAF i understand could also be the culprit.

My MAF has not been in service for more than about 20 000 miles since it were replaced by PO.
So there should be less chance that the MAF are faulty. But not necessarily without fault just because it`s fairly new though...

Problem is there could be a whole array of potential culprits so i believe following suggestions from your excpirience will work out better.