help please 3.0 hard start issue
 

Hey all, I don't have a 3.0 so can't be of any help, but a friend says his 911 has trouble starting when hot from time to time.

Said that the car cranks fine, but wont initially start, but after several tries it does.

He said that a local shop to him said it has something to do with a "thin" wire to the starter that over heats and that it is an easy fix...

Does this sound familiar to anyone and if so, can they elaborate?

Thanks

That doesn’t sound like a normal explanation. Your buddy needs to thoroughly check out his CIS system for vacuum leaks and normal system operation. Also, if the fuel filter and accumulator are old I would advise that he change them both out as a set.


-Steve

Sounds like the fuel accumulator. It keeps pressure in the line for hot starts. Here is a link for CIS troubleshooting to help your buddy.

jimsbasementworkshop.com/CIS/

If the car cranks, the starter is spinning. If the starter is spinning then the wire isn't overheated.

Thick yellow wire is to solenoid terminal 50 to engage, thin yellow is from solenoid terminal 16 to TTS and CSV circuit that aren’t used/needed for hot starts. Find a different garage...
Check for CIS component problems, accumulator, fuel check valve, WUR, air leaks etc. by testing with fuel pressure gauges.

Thanks everyone. I do know that fuel filter is new but am unsure about accumulator.

I'll pass this along!

Best

cranking and starting are 2 different things.

if it randomly does not CRANK, then look at the starter (solenoid) then ignition switch and if it has an aftermarket car alarm (remove it) look at that.
usually there is a relay installed in the wire to the solenoid and the crimps can be bad. this wires carries a lot of current to pull in the solenoid so it needs good clean connections.
you also need to clean battery connections, ground connections. don't forget the tranny to body one.

starting issue is it will crank fine but will not run.
start with ignition. new plugs cap and rotor.
check residual pressures.
check valve at fuel pump
hot start is not usually the CSV circuit.

My hot start problem was a bad fuel accumulator.

Once the car is started and hot, the fuel accumulator ensures that the required pressure for the CIS system stays reasonably pressurized, slowly de-pressurizing over time. What this means is that when the car is hot, the pressure is there and you are not yanking on the key to re-pressurize a hot engine. By virtue of de-pressurizing, the cold start system will be on line for your cold engine, and the accumulator will have by then returned the system to a (virtually) depressurized state.

Hope this makes sense. The issue for your friend may simply be rapid depressurization and hard starting. You will want to set a gauge on the pressure and watch it.

+ 1 on above with respect to residual/rest pressure.

Failed starts can lead to air box backfires which can crack the airbox.

The cost of an airbox R&R is probably five times (or more) the cost of a decent set of gauges. An average set of gauges are sold at Harbor Freight which would do a fine job testing rest pressure.

OK, I've gotten more info......

This happens regularly, but more so often when the motor is at operating temp.

He turns the key, all lights and gauges come on, fuel pump comes on, but motor does not crank.

Car has a new ignition and new starter with new solenoid.

He has tested out and the signal wire to solenoid shows 12 volts until he hooks it up, then it shows 4 volts.

He is thinking its either voltage draw on old wire or the new starter solenoid is bad.... Thoughts?

Additional information.........
 

Andy,

Do you know if the engine has CIS or carb or EFI? It is quite difficult to offer a good assessment of your friend’s engine problem without knowing the details, like fuel pressures, ignition signal, etc. Thanks.

Tony

Sorry, Tony, CIS.. Factory stock motor

Year?

77

This sounds like a starter circuit issue and not a fuel delivery issue. The ignition, starter and solenoid have been replaced so the only other item left is the wiring of the starter circuit. The contacts and components in the starter circuit wiring need to looked at for heat damage and tested for continuity. Granted, the issue is difficult since it only occurs while engine is hot.

Hi-torque starter or the hot start relay kit should do the trick.

Pat, apparently it is not only while hot, but just more prevalent when hot...

Does the drop in voltage (from 12v at the wire to 4v when connected) suggest anything?

Just out of curiosity, you have stated the car is a 77 with a 3.0 engine. The 3.0 was introduce for the 1978 SC model year. Can you clarify if the engine is a replacement?

The voltage being 12V at wire disconnected from terminal 50 of solenoid/starter when ignition turned to start would be normal.

The voltage being 4V at wire connected to terminal 50 of solenoid/starter when ignition turned to start would be abnormal. What is the voltage at the battery terminals when starting the engine?

Isolating wiring issues can be difficult and providing advise from a distance can be just as difficult. with that said I would recommend using using a test cable with a momentary switch to jumper out the starter circuit.

Disconnect the yellow wire from terminal 50 of solenoid/starter. Connect one terminal of the test cable to plus terminal of battery. The other terminal of the test cable to terminal 50 of solenoid/starter. You can now use the momentary switch to bump the starter. If the starter turns then your problem is in the wiring circuit to the solenoid/starter.

Using the schematics for a 1977 you can start from terminal 50 of ignition switch and use the test cable to supply 12V from battery. bypass (jumper out) each wire in the circuit until you isolate the portion of starter circuit wiring causing the fault. You can also work your way from the solenoid/starter to the ignition switch. Once you have the individual wire isolated you can try to repair or just run a new wire of the same color and wire size to fix the problem.

I know it is easier said than done, hopefully your electrical troubleshooting skills are at a competent level to find and isolate the fault.

The test cable can be made out of parts found at home depot. You will need the following:

Two alligator clips with rubber insulation covers.
Momentary contact (push Button) Switch.
10 feet of two conductor stranded lamp wire 14 gauge.
Also recommend an automotive in line fuse block with an assortment of fuse sizes.

I have had a home made test cable for over thirty years and have used it multiple times to isolate wiring faults.

Ok, how do I upload a movie again? I have a quick vid of trying to start but don't know how to put on page...