hupp

Checkmate,

I have found that when you change just about any single part in the K-Jet system, the car will behave differently until you tweek it back to the "sweet spot". This via the mixture screw and idle screw.

This does not sound like a wur, vacuum leak or a coil issue. The symptoms would persist while at idle driving whether warm are cold. It appears that your problem is at start up alone. No cold start fuel spray or fuel pressure bleed down. Since your shark re-starts when hot, I would rule the check out as this will allow the pressure to bleed down quickly and you would not be able to re-start hot. Bad fuel accumulators typically rear thier ugly head after the shark sits over-night, BUT will also be evident when performing the leak down check with the gauges. The system must hold pressure per the WSM to start properly and you will find that a tight fuel system will often hold pressure way past the WSM time specs.

It may also be worthwhile checking the mixture adjustment.

checkmate1996

Everyone,

Excellent suggestions so far.

As mentioned earlier, the blue bosch book and guages on their way for a full diagnostic.

Also, I tried holding down the gas pedall all the way this morning and it turned over on the 3rd crank. Noticeably faster than before. So obviously, I'm allowing more air into the system, so is this over-compensating for the lack of fuel?

I will also be taking the rear wheel off to perform a visual check of the accumulator. For all I know its the original.

I will try the cold-start trick with the bag too...that sounds easy enough...

Also, I replaced the check valve at the same time with the fuel filter as this is a separate piece for the gentleman who asked earlier. On my MY, I have two fuel pumps and both were replaced along with the fuel filter about 1.5 years ago.

No black smoke on startup. It does smell a little rich but with headers and straight pipes its hard to determine if rich or not...

I don't know if I want to mess with the a/f until the last item as I have everything running great except onstartup.....

Alan '79 928

I had a similar problem recently, although my car was hard to start warm sometimes too. I replaced a couple parts (fuel filter, check valve) and the Wur tested good.

I fixed the problem by replacing the Bosch Platinum plugs that were in there with new Bosch copper plugs. The old plugs didn't look fouled and the car ran fine once started. But with the copper plugs the car starts right up now. So that may be something worth checking as it was a cheap fix.

hupp

Checkmate,

Holding the pedal to the floor at start-up is essentially causing a rich fuel mixture. The air sensor will significantly displace the fuel piston dumping more fuel and the vacuum on the wur also drops thus reducing the control pressure also allowing more fuel. Also, all this fuel will help purge the lines if pressure bleed is the issue.

So, if what you say stands true you definately have a lean cold start condition. This can be related to the previous suggestion (ie. cold start valve, fuel pressure bleed down or mixture adjustment.)

checkmate1996

Alan,

Thanks for the suggestion. I did replace all my plugs with the Bosch copper plugs about 9 months ago. So I don't think that is it...

checkmate1996

Ahh..Things are starting to get interesting now!!

...well I should be able to atleast rule out the cold start this weekend then...

John Krawczyk

My '79 had a chronic cold start problem since i got it. I thought maybe a bad WUR. No lie, It magically went away when i replaced the leaking fuel tank.

checkmate1996

John,

You totally jogged my memory on this one. When I fill up my tank 100%, I get a leak from somewhere near the filler. I hadn't worried to too much about it as I just didn't fill up 100%. But now I'm thinking if this problem is causing another problem?

SharkSkin

Doubtful that fuel tank leaks would cause the problem. Fuel gets pumped around and around -- from the tank, through the pumps, to the pressure regulator where excess is diverted back to the tank.

If you had a problem where your cap was not allowing air to enter the tank, the tank would probably collapse at some point, and fuel flow would stop at some later point -- but if you have fuel leaking out I think it's safe to say that this is not your problem.

Dennis Wilson

Hi guys. Another possible culprit would be low voltage to the 15 post of the coil. During cranking you should have 6 to 9 volts. If too low, check for corrosion at the resistors.

When it does start, does it initially run rough? If it does, you probably have a leaking injector. To test for a bad accumulator, leaking injector or check valve, try cycling the ignition key to on then off three or 4 times then crank the engine. If it starts right up the problem is leakdown. If it is also hard to start when hot, the leakdown is probably at the injectors. If no hot start problem, check the accumulator or checkvalve.

Dennis

Optimator

Good advice. If you have a friend crank the engine, you can watch the injector and verify that it both opens and closes, stays open for the correct time range, and has the correct fan spray pattern (not clogged). I agree with others that it does not sound like the accumulator. My car had a bad accumulator. If it sat for even 1/2 hour after being driven, it was nearly impossible to start. My understanding is that proper function of the accumulator is most important while the car is still hot after being driven, as it keeps the lines pressurized to prevent vapor lock.

Dennis Wilson

Jon,

"stays open for correct time range"?????? Concerning the accumulator, a pin hole leak could cause a hard start whereas a blownout diaphram would cause a no start such as yours. i.e. don't rule out a bad accumulator.

Dennis

Optimator

Dennis,

The thermo switch controls the length of time the cold start injector stays open. I think it is typically about 8-10 seconds. For example if, during the initial cold start attempt, the switch is opening the injector for too short a time interval (like 1 second), then it is possible that not enough fuel is being delivered. I don't know that this is common, but I would think that its at least a possibility.

In Brad's original post, he described a cold start only problem. He stated that the car starts OK when hot or warm, even after sitting for 4 hours. The accumulator needs to keep the system pressurized at about 3 bar for only about an hour or so. By this time, the engine has cooled enough that vapor lock is not a concern. At this point, even if all the pressure bleeds off the system through a pinhole in the accumulator, it will not cause a cold start problem. As long as the system is filled with liquid fuel, and there is no vapor in the lines, the system does not need residual pressure for a cold start.

Dennis Wilson

Jon,

The duration should be checked by testing the thermotime switch. The only reason to pull the cold start injector is to check for leakage. The spray pattern is really unimportant considering the location of the spray.

My point about the accumulator was that leaks vary. A small leak can make it slow to start or a large leak will reduce the fuel line pressure below that required for system pressure (as in your case). BTW the function of the accumulator is keep the fuel pressure constant during engine operation. The check valve is what holds pressure when the pump is not operating.

Dennis

Optimator

I agree, but another reason to pull the injector is to see if it is clogged or failed completely.

I agree. With mine, the accumulator leak was not bad enough to prevent the car from running, but it did leak down completely less than one minute after the pump shut off. If the engine was warmed up, it typically took more than 30 seconds of cranking to clear enough air out of the injector lines before it would start.

I think you are referring to the accumulator serving to dampen pulsations from the fuel pump, which is one of the two functions usually attributed to it. I'd be curious to see how well a CIS system runs with no accumulator. I'll bet it would run just fine. If fuel pumps are that spikey with their pressure delivery, then I would think that all fuel injection systems would need dampeners - especially EFI systems.

The main purpose of the accumulator is to serve as a pressurized reservoir to prevent system bleed down due to minor leaks in the fuel system, after the engine is shut off.