Hard Starting

[Rob Gold]

I would like to find out if my problem is something that I can handle (on a scale of 1-10 I am a 2 dealing with automotive repair) or if I need to visit my mechanic.

I own a 1983 911sc cab. Last summer had the injectors changed and it runs great, after warm up it idles at around 9000 rpm.

I drive the car approximately 1x a week (it only has 43k original miles) and when I first turn the key it starts right up. After I have driven the car for a while, it has become a real effort getting it started again. I know the manual says that I should not touch the gas pedal but the only way I can get it to restart is to pump the gas a bit until the engine starts.

It actaually seems like the engine is not getting gas, the starter turns over very quickly and it reminds me of a time when the kill switch was left on and I tried to start the car.

Thanks for your advice.

Rob

[Steve@Rennsport]

Rob,

If your idling at 9000 RPM, its an F1 engine and should be healthy,...

Seriously though, it sounds like you have a fuel pressure issue and before diagnosing that, I'd recommend replacing your fuel filters (both engine-mounted and in-tank ones) before proceeding.

After that, you need that special set of CIS fuel pressure guages to measure cold & hot control & system pressures to see how the Warm-up regulator and Accumulator are working.

[Joe Bob]

#1 problem on CIS is fuel pressure followed by vacuum leaks.

[Sirius Driver]

I've got the same issue, same year model too. I replaced my fuel pump pressure release valve, and that definitely was not the issue. I still have the hot start issue.

[Joe Bob]

Hot start IF the starter spins....IS...fuel pressure related. Check valve in the neck of the fuel pump and/or accumulator are the prime suspects. When it won't start when hot, try picking up the flapper valve in the air box. It tricks the pump into running and building pressure.

[boyt911sc]

Originally Posted by Rob Gold

I would like to find out if my problem is something that I can handle (on a scale of 1-10 I am a 2 dealing with automotive repair) or if I need to visit my mechanic.

I own a 1983 911sc cab. Last summer had the injectors changed and it runs great, after warm up it idles at around 9000 rpm.

I drive the car approximately 1x a week (it only has 43k original miles) and when I first turn the key it starts right up. After I have driven the car for a while, it has become a real effort getting it started again. I know the manual says that I should not touch the gas pedal but the only way I can get it to restart is to pump the gas a bit until the engine starts.

It actaually seems like the engine is not getting gas, the starter turns over very quickly and it reminds me of a time when the kill switch was left on and I tried to start the car.

Thanks for your advice.

Rob

Rob,

Your problem is not difficult to diagnose and fix it. I would rate the degree of difficulties between 2 & 3 from a scale of (1-10). It would sound daunting at first but there is nothing to worry about. But you need the right tool to make the diagnostic tests easy and fun. A fuel pressure gauge will help you determine if your fuel pressures (control, system and residual) are causing this problem. You don't even need to run the engine when doing this preliminary test.

Are you sure you have sparks (ignition)? These are the two (2) things (fuel pressures & ignition sparks) I would immediately confirm before attempting to replace any part/s in the process. Keep us posted.

Tony

[Rob Gold]

I assume I have a spark because if I fiddle around with the gas pedal (pump it) the car eventually starts.

suggestions on where to purchase the fuel pressure gauge, and how do I find what the proper pressure should be?

Thanks

[Rob Gold]

I am going to try your suggestion, if lifting the flapper solves the problem what is that an indication of , the fuel pump valve and accumualtor you referenced in your post?

[Joe Bob]

Hopefully the check valve....it's cheap. Using a set of gauges, you can watch the fuel pressure bleed off after shutting down a hot engine.

You probably get a local person in the PCA or on the board to let you use them. They are not real expensive but enough if you don't use them a lot.

[Bob Kontak]

Even though hooking up the pressure gauges sounds scary to a learner, they really are not that bad. You just have to get up the guts to get them even with you lack of experience.

They will pay for themselves if you fix this problem.

Residual pressure means that when you turn the engine off, pressure remains in the fuel lines for a long time - like over an hour or more. You can have a beer, smoke a cigar, have dinner and watch some youtube videos and it will still have pressure. Joe Bob is saying that if the check valve that "traps" pressure in the lines is not sealed you can watch the pressure drop on the gauge as the gas bleeds back towards the fuel tank through the faulty check valve. The cold start valve sprays extra gas when you start the car cold. When warm it is overridden because there is supposed to be pressure in the system. No pressure - no start valve - hard starting when warm.

My gut feel is that one of the injectors is not sealing and leaking gas at rest causing the pressure drop.

[CharlieB]

I spent countless hours reading all the threads about CIS problems. Bought all the guages and testers. Confirmed all my pressures were spot on. Used the dwell method and a Gunston to set AFR. Tested the O2 sensor, no problems. Confirmed ECU, relay and FV, etc. were working. Then started having the same warm starting glitch that you've described. When checking hot residual pressure it would hold at 40psi for a few seconds then drop to 20psi and within 1 minute dropped to 0! Old time P-car mechanic asked me if I'd checked the primary fuel regulator in the side of the fuel distributor. My response was "The What"? I'd never read anything on these threads about anything called a primary fuel regulator. Well guess what, there is one and you can see it on the parts diagrams. Pulled it out, used carb cleaner on a Qtip, cleaned all the parts, swabbed the bore out and reassembled carefully. Cranked the engine, let it warm then shut down. Residual pressure slowly dropped to 22 psi and stayed there for over 40 minutes AND no more warm start problem. So won't hurt to try cleaning the PRIMARY FUEL REGULATOR!!!

[CharlieB]

Oh, I almost forgot. After the warm start and loss of pressure problem surfaced I did put a new check valve on the fuel pump but still lost pressure. I also checked the fuel accumulator and it was fine. My theory is the sticking fuel pressure regulator was losing all the fuel back to the fuel tank through the return line when the engine was shut down. The pressure loss was almost instantaneous!

[Rob Gold]

This makes sense for me to try first, I can't locate a picture of the pressure regulator on the pelican site, can you point me to a reference that would show me what the regulator looks like and where it is located?

Thanks for your help

[boyt911sc]

Originally Posted by Bob Kontak

Even though hooking up the pressure gauges sounds scary to a learner, they really are not that bad. You just have to get up the guts to get them even with you lack of experience.

They will pay for themselves if you fix this problem.

Residual pressure means that when you turn the engine off, pressure remains in the fuel lines for a long time - like over an hour or more. You can have a beer, smoke a cigar, have dinner and watch some youtube videos and it will still have pressure. Joe Bob is saying that if the check valve that "traps" pressure in the lines is not sealed you can watch the pressure drop on the gauge as the gas bleeds back towards the fuel tank through the faulty check valve. The cold start valve sprays extra gas when you start the car cold. When warm it is overridden because there is supposed to be pressure in the system. No pressure - no start valve - hard starting when warm.

My gut feel is that one of the injectors is not sealing and leaking gas at rest causing the pressure drop.

Bob,

The CSV (cold start valve) is controlled by the TTS (thermo-time switch) during the start phase. It has nothing to do with fuel's residual pressure. The TTS is grounded when engine is cold. At 113°F, TTS starts to open up and looses ground circuit. So you could crank the starter without the CSV getting activated at engine temperature above 113°F. So when the residual fuel pressure drops too low in the system it would result to starting problem and more harder to start warm. The engine may start, depending on how much residual pressure was left in the system. That's why when you lift the AFS (air flow sensor) with ignition switch @ ON and start the engine immediately, you could successfully start the engine because of the FP re-pressurizing the fuel lines.

Tony

[CharlieB]

Rob: You have a PM from me! Charlie

[CharlieB]

Rob: Here you go! Yours and my 80SC are a little different looking than pictured in the diagram but they work the same. The parts should be a little tight as you pull them out and likewise when you reinstall them. Make sure the little o-rings are in good shape. Just be patient and careful. I put a towel down before I pulled the parts to catch any of the usual dropped pieces. Let me know how it goes! Charlie

[WVU 911]

I have a similar problem with my 82SC, only it is when the engine is cold. Does anyone have any ideas?

[T77911S]

Originally Posted by WVU 911

I have a similar problem with my 82SC, only it is when the engine is cold. Does anyone have any ideas?

your problem is not similar, the OP is hot starting, yours is cold. trying to help both in one thread will be confusing

[CharlieB]

I'm not a CIS expert by any means. Learning something new every day. But I can give you some suggestions. Read every thread you can find on this Forum re CIS issues. Lots of knowledge out there for the newbie. Books, books and more books about CIS, K-Jetronic, etc. are available. Buy a set of guages. Kind of intimidating at first but really easy to use. Learn the workings of the various CIS components, ie: WUR, AAR. AAV, FV, etc. and how they interrelate to the system as a whole. The more you become familiar with CIS the more confidence you'll have with your P-car and the more fun you'll have owning and driving it.

[Rob Gold]

I pulled the pressure regulator and cleaned it. The o rings looked OK to me. Started the car, ran it to operating temperature and then let it sit for about 45 minutes. Same problem, but this time I pulled the air box and lifted the flapper as suggested in an earlier post. The motor started right up.

I assume this means I have a loss of pressure in my fuel system, what would be the next step?

Thanks for your help.

Rob