Engine doesn't start without throttle opening

[muc]

Do you have dual batteries? If so do you have a battery isolator installed?
Does the fuse/relay box on top of the engine have rubber mounting bushings?

 

[Wave34]

Did you say you ever checked your Throttle position sensor? On the fords it is usually close to 1.1volts in idle or throttle closed position and goes all the way to 5volts fully open. Perhaps if your boat has one the sensor is occasionally faulty. Only way to test would be to put leads on on it with egine off and test voltage. Try to start engine. If engine starts make note of voltage. If engine does not start note voltage and increase throttle and attempt restart. If it starts note voltage. Turn engine off put throttle back to idle and attempt restart and make note of voltage if it starts or doesnt. etc..

I never measured the TPS.
The reason is because after the long initial start, if I just turn off and immediately start again it does start right away.
I have that on my list like the MAP sensor.

 

[Wave34]

Do you have dual batteries? If so do you have a battery isolator installed?
Does the fuse/relay box on top of the engine have rubber mounting bushings?

Yes dual batteries with an isolator for the alternator.
There is no rubber mounts for the relay box. It is on a bracket that is metal to metal on the intake manifold.

 

[muc]

Yes dual batteries with an isolator for the alternator.
There is no rubber mounts for the relay box. It is on a bracket that is metal to metal on the intake manifold.

Volvo had service bulletins on both of these items because of all the weird problems that could arise from these two items.
Have no idea if either of them are the cause of your symptoms.
I do know you are making some faulty assumptions with your troubleshooting.
Really need a scantool in the hands of someone who knows what they're looking at.
A scan tool rarely tells the tech what's wrong. Most often it tells us what's right so we can focus on where the problem is.
It's possible one or both of your temp senders are reporting the wrong temp. But without a scantool you can only test at one certain temp. And sometimes that's not good enough.

It sure sounds like you have an temperature/electrical issue. And without being able to see what the computer thinks is happening, it could be almost impossible to fix it.

 

[Wave34]

Ok, I put some more effort in this hard starting problem.

I already had a new cap and rotor and plugs with no improvement.
I installed new Volvo spark plug wire set and it improved the starting let's say by a good 60%.
Spark was not good I guess.

I checked the voltage at the coil while cranking, and it is over 11V, so this is good.
But when measuring the coil resistance, the secondary side was below specs. Around 5000 ohms. I bought a new coil, the secondary measures 8500 ohms which is withing specs.
But the new coil didn't improve anythings.

It is a mixture problem I believe.

I was thinking that maybe the throttle plate is not adjusted correctly, and there is not enough air vs gas.

In the Volvo manual, it says not to touch the idle stop screw, that it is adjusted at factory to make the IAC valve work in its sweet spot.
But, what if someone before me touched that adjustment?

I didn't see any procedure to check the opening or angle that the plate should be at.

Correct me if I'm wrong, but during start, the IAC valve does nothing to control the air in the engine. It stays at a preset position, and the air is metered only by what the throttle plate lets pass around it.
I can't test by opening the throttle with the hand control because it will also rotate the TPS thus more gas.

Would a bad adjustment of the throttle plate cause my problem?

 

[ripjmk]

Buy a new Knock off HP Fuel Pump, I had hot start issues for a long time, it turned out to be fuel pressure leak back through the HP pump. Fuel pressure has to remain high at the instant of cranking as the pumps are not re-energized until oil pressure is above 4 psi. The HP fuel has a discharge check valve and a high pressure relief valve. Debris (or paint chips) in the check valve will cause slow leak back. Debris in both the check and relief will cause rapid leak back. The leak back will be dependent on fuel viscosity so in cold weather the leak back will be less.
After replacing my HP fuel Pump my hot start issues wen away and mr fuel rail pressure remained above 50 psi for over 5 min!

 

[Wave34]

Buy a new Knock off HP Fuel Pump, I had hot start issues for a long time, it turned out to be fuel pressure leak back through the HP pump. Fuel pressure has to remain high at the instant of cranking as the pumps are not re-energized until oil pressure is above 4 psi. The HP fuel has a discharge check valve and a high pressure relief valve. Debris (or paint chips) in the check valve will cause slow leak back. Debris in both the check and relief will cause rapid leak back. The leak back will be dependent on fuel viscosity so in cold weather the leak back will be less.
After replacing my HP fuel Pump my hot start issues wen away and mr fuel rail pressure remained above 50 psi for over 5 min!

Thanks for your feedback.
I also have a bleedback of fuel pressure when I turn the engine OFF. I confirmed this with a gauge. Went from 55 psi to 10 within a minute.

But, what makes me believe that this is not my problem, is when I turn the key ON, the pump turns ON and rises the pressure to 55 psi immediately. I wait 2 seconds for the 2 beeps to finish, then I crank the engine. Sometimes it's good, sometimes it's not. But while cranking, I have 55 psi on the fuel rail.

What I was thinking, I don't know if it makes sense, is when the fuel pressure bleeds down to 10 psi with the engine OFF, some air gets sucked back from the fuel return line and from the fuel cell. And when I crank the engine, that air gets trapped in the inlet of some injectors and has to be injected while cranking.

Where did you get your knock off HP fuel pump? Do you have an automotive equivalent?

 

[Wave34]

After 3 pages of text I tought it would be a good idea to resume my tests.

Fuel:
Fuel pressure; 55 psi cranking and running (bleeds down to 10 psi in 1 minute with engine OFF)
Checked FPR screen; no paint debris
Checked bleed valve from fuel cell; no fuel going in the intake manifold
Removed and checked the injectors; no leakage under pressure, and spray pattern was good on all of them; I cleaned them, and put new o-rings

Ignition/Starter:
New cap, rotor, coil, Volvo wire set, plugs;; I saw improvement with the new wire set only.
Checked voltage at coil; more than 11V while cranking
Power cables; 1V drop from B+ to starter; OK
0.8V drop from engine block to B-; OK
Between 10-11V at the starter while cranking; OK

Électronics:
ECT; removed and checked resistance in boiling water, down to fridge temperature; similar to chart
New IAC, and cleaned the seat and bore; no change
New lanyard switch; I tought it was resistive, but finally not
Replaced the ignition relay with the spare relay in the relay box; no change
Replaced the starter battery with a good used gr27. Tested with a load tester.
Cleaned the terminals of the power cables at the starter, engine block, and terminal block on the transom


Things to test:
MAP sensor
TPS sensor or adjustment
Throttle plate position adjustment
...suggestions?

 

[ripjmk]

The fuel pump I ordered here https://www.amazon.com/gp/product/B07V84X3GT/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
What's to loose, you've tried most everything else and its only $80.

 

[Wave34]

I will update that thread to help those that may have the same problem.
I finally found my problem. It was a leaking injector.

Why I didn't see the problem before?
One of my first test a couple of years ago, has been to remove all injectors, and test them one by one on a DIY jig that I was pressurizing fuel and look with a paper towel if there was leakage.
At that time, I didn't see any leakage. I was testing at 45 psi of fuel because my setup was leaking above that. Since cars run at that pressure, I tought that my test was concluant, since there was no leak.

FF this summer. I tested injectors for leakage again, but this time I left them attached to the fuel rail. With the 60 psi of fuel pressure that the Volvo pump outputs, I could see one injector leaking. So, 45 psi was not enough to make it leak, but 60 was.

I sent all injectors to be ultrasonically cleaned, but de leaking one was still leaking, so I ordered a new one from my GM dealer. I installed everything at the end of august and no more hard start since then.