Another CIS Hot start problem

[super9064]

I have a typical CIS hot start problem that has resisted the usual fixes new fuel accumulator or check valve replacement. I drive the car long enough to get it warm, let it sit for 15-20 minutes. I crank and crank, nothing. I tried spraying some brake cleaner into the intake, it fired just enough to burn off the vapor. It seems like it is just not getting fuel. The only thing that works is taking off the air cleaner and pushing up on the plenum with the ignition/ fuel pump on. I can hear a whoosh, then it will start after a few cranks.

Is it possible the problem may be related to the hand throttle? My car is a 73 Targa with a 76 2.7 CIS motor. The car had the hand throttle disconnected when I bought it, I’m guessing because a 76 engine does not use one. I was having a "cold start" issue that caused us to reconnect the hand throttle. I think after that I started to have a hot start problem that never really got rectified. I took it to Porsche of Annapolis and they were finally able to resolve both issues, but I noticed they had disconnected the hand throttle, but it worked fine so no problem.

My problems started again this summer after I had them reconnect the hand throttle so I could avoid stalling the car with the A/C on, the car has a lightweight flywheel and likes to stall during braking. I spoke to the mechanic and he swore he made no changes to the car other than the hand throttle. I found this during my research.

"76 saw other changes in the CIS system. The hand throttle was replaced by the auxiliary air valve, and the auxiliary air regulator. The fuel cutoff switch, located on the airflow sensor, was added as a safety feature. In '77, a vacuum switch, or thermo valve, was included to further enrich the mixture during cold starts."

That do you think? just a coincidence or can you think how it might be related.

[Charles Freeborn]

Vacuum leaks are always the first search to embark on. If it's starting cold it's because the WUR is compensating (richening). Once it's warm and mixture falls back to running level it's too lean to start.
Hand lever is merely a tad of throttle applied. You can do that with your foot.
Pretty car, BTW.

[super9064]

Originally Posted by Charles Freeborn

Vacuum leaks are always the first search to embark on. If it's starting cold it's because the WUR is compensating (richening). Once it's warm and mixture falls back to running level it's too lean to start.
Hand lever is merely a tad of throttle applied. You can do that with your foot.
Pretty car, BTW.

Agreed, but they thoroughly checked for vacuum leaks but found none.

[Charles Freeborn]

Originally Posted by super9064

Agreed, but they thoroughly checked for vacuum leaks but found none.

You got yourself a stumper there. I've found help in this book. That said my '74 has a simpler system as it's pre-smog in virtually every state.

[ossiblue]

You haven't provided the most basic information--the results of the fuel pressure tests, especially the residual pressure test. Replacing the fuel accumulator and check valve does not automatically eliminate residual pressure loss as your problem. In fact, you still have a classic residual pressure loss symptoms when pressurizing the system via the intake plunger allows an immediate start.

You need to have your mechanic run the pressure tests, all of them, and post the results. This is not a "stumper" until you have eliminated loss of residual pressure as a potential cause. You should also provide us with the Bosh part numbers for your WUR and fuel distributor as you have an engine that is not the correct year for your car.

The hand throttle, as mentioned, only allows more metered air into the intake. It is not needed in a 76 because the additional air is added "automatically" when the engine is cold by thermo-mechanical devices. From the history you posted, it sounds like a start problem was masked by fiddling with different things. Once you had it fixed and it started, both cold and warm, using the 76 only intake system, you were good to go. Now that a problem has arisen, you need to address it in the context of the system you have for the engine.

[stlrj]

Originally Posted by super9064

I tried spraying some brake cleaner into the intake, it fired just enough to burn off the vapor. It seems like it is just not getting fuel.

Looks like you're on the right track and your cold start valve does not seem to be working if you have to manually squirt the cold start mixture yourself to get it going. Make sure the thermo time switch is providing the ground for the cold start valve to work or ground it out yourself and it should fire without your intervention.


Cheers,

Joe

[Charles Freeborn]

Originally Posted by ossiblue

You haven't provided the most basic information--the results of the fuel pressure tests, especially the residual pressure test. Replacing the fuel accumulator and check valve does not automatically eliminate residual pressure loss as your problem. In fact, you still have a classic residual pressure loss symptoms when pressurizing the system via the intake plunger allows an immediate start.

You need to have your mechanic run the pressure tests, all of them, and post the results. This is not a "stumper" until you have eliminated loss of residual pressure as a potential cause. You should also provide us with the Bosh part numbers for your WUR and fuel distributor as you have an engine that is not the correct year for your car.

The hand throttle, as mentioned, only allows more metered air into the intake. It is not needed in a 76 because the additional air is added "automatically" when the engine is cold by thermo-mechanical devices. From the history you posted, it sounds like a start problem was masked by fiddling with different things. Once you had it fixed and it started, both cold and warm, using the 76 only intake system, you were good to go. Now that a problem has arisen, you need to address it in the context of the system you have for the engine.

All true. I assumed that pressure checks had been done (dictating the parts changes) Also true is to confirm that the major parts (FD, WUR, etc.) are all compatible with each other. CIS doesn't always like a "mix and match" arrangement.

[super9064]

Originally Posted by stlrj

Looks like you're on the right track and your cold start valve does not seem to be working if you have to manually squirt the cold start mixture yourself to get it going. Make sure the thermo time switch is providing the ground for the cold start valve to work or ground it out yourself and it should fire without your intervention.


Cheers,

Joe

Thanks Joe,

I don't have to use any starter fluid for a cold start, it starts fine. I Just tried that as a experiment during my hot start issue.

[stlrj]

[QU=super9064;9312190]Thanks Joe,

I don't have to use any starter fluid for a cold start, it starts fine. I Just tried that as a experiment during my hot start issue.[/QUOTE]

I was meaning for you to try it for your hot start problem since the cold start valve also works on a warm engine to prevent this problem. The thermo time switch is stamped with 45 degree celsius mark that indicates it should supply the ground for the cold start valve to operate at that temp.


Cheers,

Joe

[boyt911sc]

Originally Posted by stlrj

[QU=super9064;9312190]Thanks Joe,

I don't have to use any starter fluid for a cold start, it starts fine. I Just tried that as a experiment during my hot start issue.

I was meaning for you to try it for your hot start problem since the cold start valve also works on a warm engine to prevent this problem. The thermo time switch is stamped with 45 degree celsius mark that indicates it should supply the ground for the cold start valve to operate at that temp.


Cheers,

Joe[/QUOTE]




Joe,

Sorry to disagree with you again. You seem to be the advocate in the CSV & TTS combo. Unfortunately, you are misleading people by insisting your found knowledge how the CSV works. The cold start valve (CSV) only works when the engine is cold (113°F or below) because the TTS (thermotime switch) is not grounded at 113°F and above. What is the logic of activating the CSV during a warm start problem? You don't need enrichment when the engine has warmed up. CSV is disabled when the engine is warm (113°F and above). Do the test and share your result.

The loss of residual fuel will prevent or reduce the injectors from spraying full mist-like patterns during a hot start. And if you have unmetered air going into the system, the warm start would be more of a challenge. So without knowing your fuel pressures (control, system, and residual), you will be doing a lot of guesswork. The residual fuel pressure has to be checked and measured. No if or but........check also for the presence of ignition sparks when the engine fails to start.

Tony

[stlrj]

Originally Posted by boyt911sc

I was meaning for you to try it for your hot start problem since the cold start valve also works on a warm engine to prevent this problem. The thermo time switch is stamped with 45 degree celsius mark that indicates it should supply the ground for the cold start valve to operate at that temp.


Cheers,

Joe

Joe,

Sorry to disagree with you again. You seem to be the advocate in the CSV & TTS combo. Unfortunately, you are misleading people by insisting your found knowledge how the CSV works. The cold start valve (CSV) only works when the engine is cold (113°F or below) because the TTS (thermotime switch) is not grounded at 113°F and above. What is the logic of activating the CSV during a warm start problem? You don't need enrichment when the engine has warmed up. CSV is disabled when the engine is warm (113°F and above). Do the test and share your result.

The loss of residual fuel will prevent or reduce the injectors from spraying full mist-like patterns during a hot start. And if you have unmetered air going into the system, the warm start would be more of a challenge. So without knowing your fuel pressures (control, system, and residual), you will be doing a lot of guesswork. The residual fuel pressure has to be checked and measured. No if or but........check also for the presence of ignition sparks when the engine fails to start.

Tony[/QUOTE]

Unfortunately it seems he proved you wrong when he sprayed the brake cleaner in his warm engine and it started. However, the fact that it did not continue to run is most likely a mixture issue which is why pushing up on the sensor plate got it running too.
Joe

[ossiblue]

Originally Posted by stlrj

Joe,

Sorry to disagree with you again. You seem to be the advocate in the CSV & TTS combo. Unfortunately, you are misleading people by insisting your found knowledge how the CSV works. The cold start valve (CSV) only works when the engine is cold (113°F or below) because the TTS (thermotime switch) is not grounded at 113°F and above. What is the logic of activating the CSV during a warm start problem? You don't need enrichment when the engine has warmed up. CSV is disabled when the engine is warm (113°F and above). Do the test and share your result.

The loss of residual fuel will prevent or reduce the injectors from spraying full mist-like patterns during a hot start. And if you have unmetered air going into the system, the warm start would be more of a challenge. So without knowing your fuel pressures (control, system, and residual), you will be doing a lot of guesswork. The residual fuel pressure has to be checked and measured. No if or but........check also for the presence of ignition sparks when the engine fails to start.

Tony

Unfortunately it seems he proved you wrong when he sprayed the brake cleaner in his warm engine and it started. However, the fact that it did not continue to run is most likely a mixture issue which is why pushing up on the sensor plate got it running too.
Joe

Nothing was proved wrong.

The car starts fine when cold, enriched by the CSV and low fuel pressure from the WUR, both factors which can overcome a loss of residual pressure upon cold start. On a warm start, the CSV is disengaged and the fuel pressure is high, leaning the running mixture (reducing volume of fuel to the injectors.) Loss of residual pressure will often result in a no start or a long crank time as there is not enough (any?) fuel to ignite upon initial cranking and the pump only runs during cranking, struggling to pressurize the system. In other words, during a warm start, without residual pressure, there will not be enough fuel delivered to the engine to start and run.

A properly set up CIS is designed to start warm (above 113 F) without the CSV. The brake cleaner caused the engine to fire, but it failed to continue running which is consistent with a loss of residual pressure. Lifting the intake plunger pressurizes the system, effectively restoring a loss of residual pressure, causing the injectors to spray, and injecting fuel into the cylinders. The engine started and ran. This does not necessarily demonstrate a fuel mixture problem, but rather a fuel delivery problem which, of course, will affect fuel mixture in the overall scheme because there is not enough fuel to mix.

Everything done by the OP is consistent with a loss of residual pressure and until fuel pressure tests are done, there is no need to speculate any further. If the fuel tests come back in spec, there will be a need to look to some other culprit.