Z

It can be hard to diagnose over the internet, but the thermo-time switch is call that, instead of just the thermo switch, because it's supposed to continue to operate the cold start injector for a period of time, even after the engine has started. According to Bosch, the length of time ranges between 5 and 20 seconds, depending on the particular engine type. It's not just intended to get the engine started, but to also provide a richer mixture during a short warm up period. Basically, it's like the way a choke would gradually open on a carburated car, enriching the mixture until the engine was warmed up enough to be able to run with the choke completely open.

An initial shot of fuel is provided by the cold start injector when the starter is first engaged. If the "time" function of the thermo-time switch isn't functioning properly, the engine may start or fire briefly from that initial shot of fuel, but won't continue to run beyond that. It's like quickly opening the choke all the way on a carburetor immediately after a cold engine equipped with one is started.

Hacker's '79 had a cold start problem. It now has a push button switch installed to manually activate the cold start injector, in the same way that a manual choke would be used. Car starts and runs fine when cold now. This was just done as a temporary fix, so that the car could be driven, because the car will be getting switched to a different engine management system anyway.

If you still suspect a frozen fuel line, check for fuel pressure when the engine is refusing to run. If you've got fuel pressure at the rail, it's not a frozen line or pump.

j.kenzie@sbcglobal.net

Thanks Z,
As usual you are correct. I used to have a fuel rail pressure gauge, but don't anymore. I replaced my TT switch about 4-5 years ago as preventative maintenance.
Great idea though. I will check, I remember W and G and resistance.
Dave

j.kenzie@sbcglobal.net

Hi again,
It's 21F. right now and my car parked outside for 12 hours started perfectly tonight. I am hoping that running some gas defrost products through the system solved the problem. This was very common when I was a kid, 1960, I had not run into it for a while. Still it is not -2F. like before. On the other hand this car has driven through 6-8 Chicago Winters before this without problems.
Dave

j.kenzie@sbcglobal.net

An update: Problem still there.
Minus 3 degrees today. After behaving perfectly, for the past few weeks, car was again very difficult to start. It turns over well, fires, then wants to die. By feathering the gas pedal, I just kept it running at about 1000 rpm, to let it warm up. When it first reached operating temp, it would not rev easily past 1200 rpm, and would die if I removed my foot from the gas pedal. I nursed it up to 2000 rpm, and held it there for a minute or so. Good voltage, good oil pressure. Finally I could drive off very carefully, but still not normal throttle response.
I parked it in my wife's spot of my heated garage.
Any more ideas would be appreciated. Just for fun, yesteday, I checked for free motion of the AFM barn door, and it seemed fine.
Thanks,
Dave

j.kenzie@sbcglobal.net

Hi again,
I checked the ohms on my temp sensor and thermo-time sensor, and they both seem OK. I pulled my AFM and checked the ohms per WSM and it seemed close but not perfect. I did notice some foamy liquid in my intake just beyond the O-ring that seals the AFM. It did smell slightly of gasoline, but not pure gas?
I checked the vacuum connectors at my fuel damper and regulators, and no gas smell (also with Mity-vac, and they all held full scale 25-30 psi).
Anything else come to mind?
Thanks,
Dave

Fogey1

How was the driveability/throttle response after it was fully warm?

Z's thoughts still seem plausible and exactly on point to me, especially about Hacker's experience and work-around. That kind of switch should be easy to jury-rig as a test.

Good luck.

Another thought - How's the green wire? You could also be describing a challenged ignition system.

j.kenzie@sbcglobal.net

I also checked auxilliary air regulator. It shows 17 ohms across its terminals, and it should be 40-75. Not sure if that's bad enough to cause problem or not.
Dave

GregBBRD

Very common.

Fuel filter has water trapped in it.

Change filter.

j.kenzie@sbcglobal.net

Thanks, Fogey. New green wire. I had a cold start rewire, where I get cold enrichment as long as starter is cranking. Ptroblem was same then and stock cold start now. I could maybe figure a push button. Again, this is new compared to years past.
Dave

j.kenzie@sbcglobal.net

Thanks, Greg.
I will do.
Dave

j.kenzie@sbcglobal.net

Hi Greg,
How can I keep this from happening again?
Thanks,
Dave

dr bob

I'm gonna go with "don't put water in the gas tank anymore" for $400, Alex.

We generally don't have much control over how much there is in the gas we buy. Our winter blends here still have enough ethanol to grab any water and keep it from freezing. But alcohol as gas-line anti-freeze certainly has it's limits. You can do a simple experiment by heating the fuel pump and filter some with a heat gun, and see if the problem goes away. Or test the fuel pressure with a gauge and see if a) it's low now, and b) if it gets better with the filter warmed up a bit.


I don't know much colder than maybe 25ºF with the 928, and it started and ran fine the few overnights it enjoyed at that temp.

My memory harkens back to a chilly mountainside construction camp in Indonesia, with sometimes 40º mornings. The local Diesel fuel was not intended for cold or the altitude, and would solidify with all the wax/parafin in the cold. My driver would be out early, and build a little campfire under the fuel tank to warm it up enough to start the engine. The little Mitsu combination mini-van/pickup didn't have any heater, but did have AC that would blow an icy fog on a hot day down closer to sea level.

Don't build a campfire under the 928 fuel tank...

Avar928

I've been able to successfully start my 928 on first crank in low teen temperatures. She'll sound weak at first, especially when cranking, but will catch. I actually attribute the weakness at severe cold due to the battery. Dash volt meter hovers close to 10 on really cold days and 11-11.5 on warmer (50+ F). I could be wrong and maybe the cold weather somehow exacerbates a small parasitic drain somewhere on the car that I haven't tracked down yet.

19psi

Using 10% ethanol will NOT void your warranty and the manual does not state that anywhere.

Page 6-4 of the 1997 Chevy Blazer owner's manual:

In addition, gasolines containing oxygenates, such as ethers and ethanol, and reformulated gasolines may be available in your area to help clean the air.
General Motors recommends that you use these gasolines if they comply with the specifications described earlier.

Methanol is what will void your warranty.

j.kenzie@sbcglobal.net

Hi again,
Well it's minus 3 degrees F. in Chicago this morning. I have a new fuel filter. The car gave me the same problem. Very difficult to start. It would only hold an idle if I very carefully feathered the gas pedal. It would not rev over 1200 rpm until it had idled for about 20 minutes. Then it rather suddenly began to have a normal throttle response.
I did not drain my gas tank. I try to keep it full in the winter, and I don't have a place to put 18 gallons of gas. I am tempted to put a couple of gallons of E85 in my tank. Would that be a problem, or would it be a way to incorporate any residual water into the fuel?
Thanks as always,
Dave