Hello all,

I am the proud new owner of a '79 928 5-spd and I am currently trying to get a handle some maintenance issues. I've done most of the basics: New plugs/wires/rotor/distributer, checked timing, inspected vacuum hoses, etc. The car runs good once it's started and warm, but it has been difficult to start when cold (after sitting for a couple of days). At times, I have had to crank to the point of risking draining the battery -- she would keep teasing my by almost lighting off then quickly sputtering out. Warm starts can also be an issue, she'll crank right up but mis for a moment or two before settling down. The idle speed seems to be somewhat erratic as well (after warm up period, of coarse). Once warm, the car may idle at 800 rpm but after a some driving the idle may settle at 1100 rpm. I've adjusted the idle screw to no avail.

Other observations include:
Fuel pump continues to run with key in on position -- should the pump stop after a few seconds?

Cold start injector is wired to the intensive wiper wash button- WTF? Press the button to prime engine instead of relying on thermal switch.

Small diameter hose exiting the firewall (adjacent to red heater valve hose) is just dangling loose. Started car and place my thumb over hose end and did not feel any vacuum. Any idea where this hose is supposed to attach?

Any ideas folks?

 

Sounds like the first problem you have is the small valve back by the fuel pump that is supposed to keep pressure in the fuel line for quick restarts even after sitting for a while. When this valve is bad, fuel pressure leaks down and the pump has to run for an extended period of time to build it back up before the car will start........this is why your fuel pump runs more then a few seconds. The check valve is pretty cheap and a common item that needs to be replaced.......any of the big three suppliers will know exactly what you need. I'm not a guru of the early cars so the rest of the problems I will leave to others on the list.......good luck!

 

MikeN,

Thanks for the input. I should add that the fuel pump check valve has been replaced recently - by the previous owner. It is possible that the check is bad - you know what they say " If you want things done right ..."

 

Congrats Hupp,
I'm really enjoying my '79. I think you'll realize what a piece of engineering you have once the work of getting the bugs fixed. My fuel pump only runs when starting, and then when the engine is running. Otherwise, it defaults to off.
Hey, thanks guys. I was going to ask the same question. Check valve, eh? I love these little problems. I know, I'm weird. I guess it's just being used to carburetors, I like something new. Besides, carbs just seem like such glorified toilets to me. Injection is so cool.

 

Greg K,

I've already realized how well built the car is, even by today's standards. I actually enjoy working out the bugs as well. I'm starting to suspect that the fuel pump relay has been by-passed. The relay apparently communicates with the coil in order to determine when the engine is cranking. Once the engine stops cranking, the fuel pump should stop -- a safety feature designed to stop the fuel from spilling out in the event of an accident. The only time the pump should run without the engine cranking is before starting to build system pressure.

By the way, have you changed your injectors? Any tricks/snags that I should be aware of?

 

uhm, first of all I think your fuel pump needs to be running all the time. How else will the motor receive fuel to run?? Constant fuel pressure must be there.

Before you go diving off into suspecting things you are gonna have to check your systems out. and by systems I mean fuel delivery, spark delivery and vacuum.

First off you need to pull the spider off. Its really not that bad a job. and you need to replace every rubber vacuum line you have. Mine all inspected okay looking but after getting into it I had many of my hoses with small cracks or they were hard and brittle and leaking around the clamp. I fixed half of my problems just by replacing hoses. And it wasnt that costly. I went to pep boys with my old ones and just bought various types with the same type of curves and bends.

Next, you need to check your fuel system. Buy or make a fuel pressure guage and per the manual check all your fuel pressure values. Its quite easy to do as long as you follow the manual. Again I had some pressures that were off a bit. I readjusted and the car idled and ran much better. The tester I made maybe cost me 25 bucks. You dont know who has been messing around with the CIS system so you need to put a guage on it and find out.

Next, you need to check your electrical system. It isnt hard because our cars are very simple electronically. Again follow the manual and its very easy. You need to have a multimeter for testing but again you can pick one up for 20-30 bucks at most. I got mine at harbor frieght for like 25 bucks and it does everything. Test your plug wires also. Unscrew the ends and test for continueity. The manual tells you how to do it.

You have to go through those three systems first to make sure they are all working.

 

You may have a faulty fuel distributor. I had the same symptoms years ago, replaced the easy things like check valve, but eventually had to replace the fuel distibutor to solve the hard-start problem.

When you crank the engine and it doesn't start, the fuel pump should run for a second or two then stop. You can bump the starter and hear the pump.

When you remove the injectors, they unscrew from the runners. Be careful, when you turn the injector it can strip the sleeve that screws into the runner. Maybe soak in Liquid Wrench, etc. before you remove them.

Good luck.

Rich.

 

Thanks for the info guys and, just for clarification, I understand that the fuel pump should run "while the engine is running (I used the word cranking and meant running)." The point I was trying to make was that my fuel pump never stops as long as the key is in the on position. It will run continuously - engine running/not running/stall whatever the case.

I need to get my hands on the shop manuals; however, they seem to be hard to get. I've talked to the guys at 928 Intl. and the books are on back order - for about a year. Is there any way I can get the manuals sooner?

 

OH, didnt realize that the pump was running all the time with the key on. Okay then, pull the relay, does it still run, if not its probably a bad relay. what if you pull the fuse. that should kill it, if not then someone has re-wired it to be hot all the time when the key is turned on.

I also replaced my ignition switch about two months ago. I had a no start case where I would turn the key to start and get nothing, that is nothing at all, no starter, no fuel pump noththing. but then I would come back later and it would fire right back up. I replaced the ignition switch and have had no problems with anything since then. It was a good investment for me since I had the pod off to do a odometer fix.

Manuals are hard to get, thats why you should buy the cd version until you can come up with a set of manuals. someone on the forum here sells the cds. someone will pipe up. its definately been worth it for me. its kinda hard to find things fast but its easy to print just a section out and use it to work on your car. write things down on it and save them for later, that kind of stuff works great. buy the cd you will like it for sure.

 

Thanks Curt,

The CD version would be great! If this thread does not elicit a response from the "CD Guys" I'll probably start a new thread.

Richard mentioned a faulty fuel distributer. Will a faulty distributer cause the car to run poorly? Mine runs like a bat out of hell once it's lit off.

 

In my case the fuel distributor only caused difficult starting. The car would run fine after start-up and full fuel pressure in the system.

Rich

 

My car used to start on the touch of the ignition key.
It now takes several seconds on the starter to fire up.
It the runs fine accept when it is cool weather it revs up and down until its warm.
I spoke to a local Porsche garage and they adviced me to start trying with Redline injection cleaner .
They also sayed that it might need an CO adjustment to get read of the variating revs.
If Redline would not do the trick they suggested to remove and clean the injectors and in worst case have them replaced.
My car has spent to much time in the garage this year, that's why they guessed that injectors were possibly leaking.
(Also based on the black sparkplugs)
These babys needs to be on the road.

 

Peter is right. The more you drive these cars the fewer things go wrong. Like oil leaks. I had several oil leaks that just went away on their own because I have been driving the car about every other day now.

As far as the fue distributor goes, I would try everything else first before pulling that thing out and having it replaced or rebuilt. That could cost some bucks. I think I would build a fuel guage and take some readings per the manual. See how things look after that. Then make a few adjustments if needed. Its been about 6 or 8 months since I last took fuel pressure readings. I have been driving the car much more since then so I really should take the readings again to see if things have changed. I also adjust fuel mixture on a monthly basis. I have installed an O2 sensor so that I can take readings and make my adjustments. I feel that is a must to fine tune these things.

 

Curt is correct, the fuel distibutor costs $$$$$$$. Do everything else first. You may solve your problem before going to the expense of a new fuel dist.

Rich.

 

LOL! Maybe I need to step back to a '79, because I'm certain that quite a bit of my 86's 4100lb curb weight is wiring. But it's not the sheer amount of 10,000 power options that's the problem - it's former owners and their poor choices in electrical repairs...

I would fully investigate this and look for other "odd mods" related to cold starting.