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On my 82....should the fuel pump kick on when the ignition is turned on for the first time when cold? I,ve heard some years they did and some didnt. Mine, I only hear the pump kick on after the first attempt when the engine is cold..Its had a cold start issue since purchased and I,ve replaced the fuel pump relay ( bought a used one if I recall), temp 2 sensor,cold start injector and have installed a new ignition switch. These have cleared up quite a few issues the car had,but the cold start issue is still there.
I believe it should for about a second and shuts off until the L-jet senses ignition pulse from a turning engine. Test your temp-time sensor, it is expensive but mine was faulty and with a new one my car starts immediately no matter the temperature. Check manual page 24-17 for testing.
Majestic. ..I checked it a while back and it was out of spec. I've been trying to get a hold of a good used one just to be sure. I've been trying to keep the budget reasonable and I've been working on all the other issues that this 928 had. Most issues have been fixed. ..except this. . When cold, Or the First Start Of The day, I dont Hear The pump Kicking on, but maybe the time switch is Affecting it.
The temp-time sensor is only used to control enrichment at start up, nothing to do with the fuel pump - if the contacts are closed (cold), current passes to the cold start injector, while cranking. The pump relay on early CIS cars turns on the pump for a few seconds at turn on, then off - if ambient noise is low the pump should be audible, but its easier to check with somebody under the rear. The pump then next comes on when the relay sees ignition pulses . Not sure if this is the same for L-jet. L-jet systems have the pump relay triggered by a switch inside the air flow meter, indicating that air is being sucked in, meaning the engine is turning, either running or cranking.
jp 83 Euro S AT 57k
Unlike every FI vehicle I've ever owned, my '82 does NOT run the fuel pump when the key is first turned to on. It always starts instantly whether it's 110º or -10º or even during first start in the spring after sitting all winter.
My fuel pump relay appears to be nothing special vs. others with circuit boards like the headlight relays. Definitely no timer circuit in it.
Not long after I bought the car, I began having starting issues only when hot and that ended up being an inexpensive check valve on the fuel pump. I assume there is no need to "prime" the system due to the check valve. However, a bad check valve doesn't seem to affect cold starts.
George, thats what I was looking for. I,ve suspected the Temp time switch but have been working on other issues on the car. I dont hear the pump kicking on until I,ve turned the engine over, then once it finally starts,it will start fairly easily the rest of the day. I just wanted to verify that the pump not kicking on was normal for the 82s, and it sounds like it is. Thanks to all for the help!
Chuck
Pump kicking on is normal for 84 and back US 928s and 83 and back Euro 928s.
The fuel pump relay is special in the early cars and includes a 5th pin off to the side that allows the system to prime before starting. PN #: 928 615 113 01
A standard 53 relay can be subbed in but the pumps will no longer prime.
The system in both cars also gets the signal to run the fuel pump(s) full time from the ignition box, which sees the signal from the hall sensor in the distributor.
It has nothing to do with either fuel injection system sending a signal.
My reading says the 5th pin on early relays is the input from ignition pulses, and the prime at turn on is just something built into the relay, with a timer to cut off if no ignition pulses.
To Chuck, if you can hear the pump start while you are cranking, thats a pretty noisy pump, and I would suspect its expected life is short. I can hear mine start at switch on inside the garage, but only by concentrating, with the driver's door open. If you have no adverse symptoms, leave it alone. If you do get delayed start up, Roger carries the priming relays at good prices.
jp 83 Euro S AT 57k
The common relay uses a timer that watches for a pulled-low tach signal to happen. If that doesn't happen in a second or so, the relay opens. Specific relay timing circuits have varied over the years, with many aftermarket relays now using a rather common 555 IC timer to take care of the duty, vs a RC and transistor timer in some of the originals. The transistor looks for a tach pulled-high signal. It's a subtle difference, one that determines whether the pump runs before the engine actually cranks.
Petza sent a couple of expired relays for a look, and my intention is to come up with a plug-in that will allow use of a replaceable relay that will plug into the 555 timer board. Modern cars use a miniature relay rated at 40 contact amps that's a fraction of the can size of the original pump relay, so it should pretty easily handle FP load if a proper protection diode is added across the contacts. I lost my local CIS "test" car when Jim Chambers sold his '78, so this project has sort of fallen on a back burner for a bit.
Another cause of hard starting could be the fuel pressure regulators leaking and thus allowing fuel pressure to bleed off back to the tank when the car is off. Pull off the vacuum lines and sniff for gas or dip a toothpick in to see if it is wet inside. These are at the back of the engine.
Thank you all for the input...heres a little more info..
1.. I checked my receipts..the fuel pump relay,I did replace that with a new factory relay this spring
2..The car did come with a new fuel pressure regulator in with the spare parts...I replaced the one on the drivers side with this one. the other side may have issues. I did note while checking fuel pressure and flow (which were in spec) that the fuel pressure did bleed down fairly fast when the pump was shut off. ( within a minute or so)
3..I do hear my fuel pump running,even with the doors close and the car idling...and this car has the muffler bypass installed so its not a quiet car.
4..A gentleman who actually owned my car a few years back told me that its always had the cold start issue,at least since he owned it. Going through the stacks of receipts and invoices,I dont see anything as far as the temp time switch being replaced..lots of other parts,but not that..it may be the original. Chuck
Another cause of hard starting could be the fuel pressure regulators leaking and thus allowing fuel pressure to bleed off back to the tank when the car is off. Pull off the vacuum lines and sniff for gas or dip a toothpick in to see if it is wet inside. These are at the back of the engine.
Majestic....just wondering.....if one of the regulators were leaking by and causing a hard cold starting situation...wouldnt jumpering the fuel pump relay bypass this issue and expose the problem as being one of the regulators? When checking fuel flow and pressure we jumper the relay,and if the thermo time switch is working,it seems like the car would start normally as the pump is up and running and providing the fuel pressure needed to run?
Your thinking sounds correct to me, though you stated that the temp-time sensor tested out of spec. At this point, knowing that the temp-time sensor is bad, replacing it would be my first move. You will not get easy cold starts without it so looking elsewhere for a problem is chasing after the wind.
With all system functioning, the engine should start with authority before it even feels like it has completed a single revolution.
Thanks. when I first bought the car and was going through all the basics,I did try to start it with the relay jumpered and it was still a very hard start when cold. In an earlier post someone mentioned that the specs in the WSM may be incorrect for the TTS,so even though it was reading out of spec,I decided to address all the other issues that the car had before making a decision on what was needed. After repairing and replacing so many plugs and sensors and whatever,the cold start issue still is there and with the relay jumpered it still starts hard. The time switch is probably the original and I,ll be replacing it as soon as I can! Thanks again!
The TTS should power the cold start injector while cranking, for a short period - no of seconds is usually stamped on the body. If you suspect its failed, check first that power is arriving at the cold start injector while cranking. If it is, check next that fuel is coming out of the cold start injector while cranking - the cold start injector may have failed, or fuel is not getting to it. These are a common item - 911 part no, item 32 on above diagrams.
If no power to cold start injector while cranking, check that power is getting to TTS, and if not, trace that issue back to the main board.
jp 83 Euro S AT 57k
11-28-2017, 04:17 PM
82 928s....fuel pump question
. When cold, Or the First Start Of The day, I dont Hear The pump Kicking on, but maybe the time switch is Affecting it.
