Cold Start ... Blup Blup Blup (Low Rev) ... Then Idle Settles

[mca]

In recent weeks I have been experiencing unusual revs when I first start the car.

It used to rev high and then settle into a nice idle, it now revs LOW and then settles into a nice idle. After that initial slow turnover, it is completely fine - does not behave this way when warm.

Is this a sign that the accumulator is beginning to fail? Or is it the warm up regulator? Or something else?

I am guessing that it isn't the WUR b/c it starts fine when warm.

Thanks,
Craig

[Paulporsche]

It could be your WUR or, maybe even more likely, your Auxiliary Air Regulator (AAR). The function of the AAR is to keep the revs up during the warmup phase.

[mca]

Thanks Paulporsche.

AAR and WUR ... anyone else have ideas or should I run with these two suggestions?

[hbkramer]

Suggestion...Fuel flow is first step to correct diagnosis... She needs 1 lt. for 30 sec comming from the pump.(test it from luel line going into the accumulator.
If less than 1l/30 sec., replace your fuel filter check again .If less than 1l/30 sec replace fuel pump-and check valve....Then go after vac leaks,wum, aar etc.
If you are not getting correct fuel volume the rest of the system/problems will be hard to diagnose properly.

[boyt911sc]

Craig,

First and foremost in CIS trouble shooting is to determine your fuel delivery system characteristics. You could either check it by volume or pressures. I tend to like measuring the cold control and system pressures than measuring the volumetric flowrate. Either way, establish a the baseline performance of the fuel pump and proceed from there.

FP,WUR, CSV, AAR, FF, FA , TTS, etc. (major CIS components) including fuel injectors are easy to test individually for performance. Since these components work in conjuction with one another in someway, finding the culprit needs some methodical approach.

In your case, I would surely eliminate CSV and TTS (cold start valve & thermotime switch). With this limited information, my quess would be either FP, WUR, or AAR. Or some other thing. Do you have a fuel injection pressure gauge kit?

Tony

[mca]

Originally Posted by boyt911sc

Do you have a fuel injection pressure gauge kit?

Don't have a pressure gauge kit. I will certainly be adding that to my Pelican "Project List" (wish list).

The fuel pump is less than 1 year old. I installed a new fuel filter two days ago.

Can't I elminate vacuum leaks and fuel volume/pressure issues if the car runs perfectly after the intial low revs? Wouldn't I being experiencing other problems?

At this point, all indicators point to the WUR or AAR.

[mca]

The auxiliary air regulator heats up and closes off additional air from entering the injection system after the car has warmed up. Rough running when the car is hot may indicate a defective unit that has stuck open.

I don't have these symptoms. Not an issue of running rough when hot.

I hope it isn't the WUR either after seeing the prices.

[mca]

Originally Posted by boyt911sc

In your case, I would surely eliminate CSV and TTS (cold start valve & thermotime switch).

Tony ... why eliminate the cold start valve?

"The cold start valve supplies extra fuel to the engine when starting the engine cold. A non-functional valve results in poor idling and tough starting when cold."

This describes my problem perfectly. Seems like engine isn't getting enough fuel the first time I turn the ignition.

What do you think?

[hbkramer]

Not to hijack mca's thread, but I am curious as to why the sys pressure is ok and the f.pump volume is not to spec.
My cold sys. pressure is ok(4.9 bar) and my fuel pump (at the bottom feed comming off the fuel accumulator is only delivering 300ml/30 sec.) ps I also replaced the filter and got the same results.

Hence the question can you obtain a good sys pressure(4.9 bar) with a weak fuel pump that's only delivering 300ml /30 sec??? I think you have to have both the flow rate and pressure to spec before you get an accurate diagnosis of the system. (Tony? what do you think.)

Mmy car is exhibiting the same cold idle roughness/ hunting condition and I also feel it is starved for fuel-
I thought the issues may be similar.sorry I should start a new topic.

Ps. the sold start valve is getting voltage from the thermo time switch but I have not checked the flow of the CSV injector...It seems is impossible to remove it w/o a partial engine drop. I think you need to check it as well.
bruce

[boyt911sc]

Craig / Bruce,

First of all, I'm not an expert but find CIS trouble shooting simple and fun. The CSV valve works only at initial start-up when you crank the starter and the engine temp. is cold (temp. at which TTS is closed). I have not tested my TTS but my quess is 65 F & below. Secondly, the CSV gets power from the yellow line coming from the starter and ground line from TTS. So the CSV will only inject additional fuel when the circuit is closed (cold engine).



A high cold system fuel pressure tells you that the fuel pump is capable of deliverying the required volume. Pressure reading between 65 to 70 psi is ideal for an SC engine.

A good WUR should give a low cold control pressure. I like it to be bewteen 15 to 25 psi and could easily start the car in dead winter. As the engine gets warm up, the hot control pressure creeps up slowly to 50+ psi.

Bruce:
There should be no fuel flow from the bottom of the fuel accumulator unless the diaphram is broken. Maybe you meant fuel filter.

I find it more convenient to use the fuel pressure data than flow rate (cc/min.) and could readily relate the performance based from an established baseline data.

Craig:
You need some fuel pressure readings to make a sensible diagnostic evaluation. Without such information, it will be a trial and error trouble shooting.

I'll PM you guys. Thanks.

Tony

[JFairman]

Mine does the same thing sometimes.
It's the aux air valve sticking shut so it isn't open when the motor is cold.
The aux air valve lets some air bypass the throttle butterfly at idle when the motor is cold, raising the idle speed so it doesn't stall.

The warm up regulator richens the fuel mixture by letting less fuel return to the gas tank, therefore forcing more fuel out of the injectors... making a richer mixture.
Thats the simple explanation without talking about control pressure...

[T77911S]

you also need to check the slow turn-over- either battery or starter. if the CSV does not get enough voltage- due to a weak battery it will not fire, although you say it starts but just idles low til it warms up sends me back to paul- the AAR.

[Noah930]

Originally Posted by JFairman

Mine does the same thing sometimes.
It's the aux air valve sticking shut so it isn't open when the motor is cold.
The aux air valve lets some air bypass the throttle butterfly at idle when the motor is cold, raising the idle speed so it doesn't stall.

The warm up regulator richens the fuel mixture by letting less fuel return to the gas tank, therefore forcing more fuel out of the injectors... making a richer mixture.
Thats the simple explanation without talking about control pressure...

So, if the motor sputters during cold starts, but seems to run/idle OK during warm starts, how can you differentiate between the AAR and WUR as being the culprit?

What if the motor sputters during both cold and warm starts (though more frequently during the cold starts)?