Alan

I haven't been driving so much the last few due to having some old rubber on some loaner wheels - but I have noticed slower starting when cold - maybe crank for 3-4 seconds before starting ~normally (twice as long as is typical for my car). However when hot (and ambient is ~ 100-110F) restart is much worse. Maybe 10 seconds cranking and a hesitant start, sometime idle isn't quite stable at first and you have to give it some gas to keep it running.

The symptoms seem a bit like fuel starvation, but once running smoothly no more issues, and at high RPM it runs fine.

Initially I though it might be injectors leaking but most of a tank of gas with injector cleaner made no difference. The fact that its worse on an immediate hot restart than first thing in the morning cold also argues against that. What can cause slow fuel pressure stabilization esp. when hot - fuel regulator/damper? I'll need to get a fuel pressure gauge on it - but heading out on vacation tomorrow for next 2 weeks so it will have to wait until I get back.

Other ideas?

Alan

dr bob

Alan--

This is the situation for which that little fuel pressure gauge on the end of the rail was made. Don't leave it on permanently of course, but do put it on and take a look at pressures prior to starting both cold (such as it is in Phoenix in July...) and hot. There are a few paths for fuel pressure to leak down, including the 8 injectors, regulator, 2 dampers, the check valve at the pump, and then all the plumbing. When the engine is hot, fuel will vaporize in the system if pressure isn't maintained. Under that condition:

-- When you crank the engine, the pump needs to refill the system with liquid plus cool the plumbing including those hot fuel rails to make sure that liquid is available at the injectors.

-- A leaking injector, or a failed diaphragm in a damper or the fuel pressure regulator will bleed fuel into the intake, creating a very rich mixture that will need to be cleared out with a few engine revolutions before it will fire.

Since you notice slow starting when it's been sitting longer, a leak anywhere in the system still adds some time to the starting process as the pump needs to refill the whole system with liquid. Your summer "cold start" conditions, maybe after sitting all day or even all night, are still plenty warm enough to flash fuel in the manifolds if the pressure is allowed to bleed down.

----

It's the heat of summer here today, likely the last days of the year that we'll see high temps. Mid 90's with 15%RH is forecast. Overnight lows were high, like low 60's, making this the hottest of the season. It's typically around 50 or less overnight, so we can cool everything off just by opening a few windows. AC ran for an hour yesterday as K was working upstairs and forgot to close a few windows as the temps came up. Based on those temps and the 928's use pattern here, it might see half a dozen "hot" starts a year.

Thought you were headed off for vacation....

Alan

Yes - and actually the engine doesn't still need to be very hot for it to be a slow start - even 4 hours after shutdown at 110F ambient will be a slow start, so that makes sense. I doubt now it's an injector, but all the other culprits are very possible.

...and yes:
Alan

James Bailey

Plus "giving it gas" is actually just giving it more air another indication of too much fuel in the intake.

Alan

True it's a big misnomer....

But who would immediately understand if I said I had to step on the air pedal to keep it running?
Even when we come closer and talk about more throttle - it should really be less throttle

Alan

James Bailey

Less throttled.....

19psi

Do you have a check valve on the fuel pump like the older models?

worf928

Besides the above-mentioned...
What's the condition of the Mass-Air Sensor?
When was the last time you checked TEMP-II resistance values at the LH/EZK pins?

OTR18WHEELER

I won't be able to fill a whole page but, to me, symptoms seem to lead to a fuel pressure regulator.,

Alan

Dave MAF was JDS reconditioned about 7 years ago - car runs perfectly fine apart from the starting issue. Temp sensor is a possibility but there are no other aberrant running symptoms once started and settled. I'll take a look when I get back - Too busy packing right now.

Alan

Mrmerlin

easier test hold the pedal to the floor when hot,
see if starting is faster if so then you have a leak in the damper reg or check valve or injector.
use startron and 6 oz MMO in the gas and techron every 3K miles

dr bob

Stan, what's the benefit of adding MMO to the fuel? It's mostly mineral oil (unless the formula has changed radically in the last 50 years or so...). It was a big help on carburetor cars as it would tie up water in float bowls and slow corrosion in jets and tubes. In FI cars, it can help do those things in aluminum-cased fuel pumps. Other benefits to regulators/dampers/injectors?

Mrmerlin

the MMO keeps the injectors working better as well as the fuel pump, you may notice slightly quieter operation/
The Startron will eat the ethanol,
the Techron will dissolve hardened deposits,

the ethanol is not the best thing for any part of the injection system

polecat702

Stan,

Due to a government mandate, we add 10% ethanol at the rack where our tankers load, to raise the octane rating in the gasoline. If the Startron eats the ethanol from the gas, does it lower the octane rating?

FWIW, I've used MMO, as long as I've been driving, my cars love it. Been using Startron in my trawler for years to preserve the fuel. And my cars in storage.

King928

James, et al.

On the comment of "giving it gas"...This is what i have to do on more occasions than I prefer for my hard start...she will often start right up, other times i have to give it gas.

My master tech suggested to replace plugs, wires, and distributors as i am trying to get her on the maintenance schedule...Not sure the last time they were all replaced.