Heat soak no start

[98v70t5mgonegray]

Warm start/ heat soak no start condition.
1998 v70t5 manual
2.3 liter early style with returnless fuel rail.

Ive owned it for roughly 5 months.

Before issue presented replaced.
Misc engine mounts, suspension mounts, subframe mounts
Abs/tracs repair
Air pressure sensor
Evap canister lines, 2 were open to air.
MAFS
Flametrap/pcv
Timing belt, tensioner

Trying to get it to a zero tune status, and getting codes cleared.

Maybe 3 days after Timing belt kit/ oil change. this problem first presents, the car starts cold like always, and will run forever.
Warm shut off and immediate start back up will happen with a bit of labor, stumble and find idle.
If you shut it off and wait 10 or 15 min, you will have to wait another 15 to 30 min. No matter how many times you try, it wont catch. It cranks fast, It will cough and start to start, but not get it all together.

Disconnected the new mafs, didnt help.

Since this issue presented I've replaced.
Fuel pump relay
IAC valve.
Coolant temp sensor (was reading 275 ohms at warm not the 300 that its stated it should).

At this point I started investigating the possibility of additional unmetered air, I sprayed carb cleaner everywhere looking for vac leaks.
Pulled the fuel rail and checked for leaky injectors.
Replaced evap canister shut off valve. (The lines to this valve had like old bad gas in it, more than several drops.)
That didn't fix it.
I Isolated the evap canister purge line to the intake, did not fix it.
I replaced the plugs, wires, cap and rotor.
Runs smoother but problem persists.
Ordered a fuel pressure gauge.
Read fuel pressure at 38psi in key 2 position and 32psi running.
Replaced fuel filter. No change.
Replaced the fuel pump.
Fuel pressure now 42 and 33 running.
That seemed low running, ive read its supposed to be like 36.
I disconnected the vac line to the fuel pressure regulator, when running it was keeping 42psi.
(Test to see if the
Car would start better warm with higher fuel pressure)
let it warm up and still the same starting issue.
I then replaced the crank and cam sensors.
Its still there.....

There are two things to note.
From day one, on a cold start initial revs to 2100 rpm (unusually high, but because the warm start issue didnt start until a month ago could be unrelated.)
Second thing every once in a while it has a studder in the idle. Maybe once every couple days, just quick and back to normal.

Any info on what hot start looks like different from cold start?
all the sensors it uses for start up?
If evap purge happens during startup or not?
What air is supposed to be flowing whats not?
Any insight on a ground near the front of the engine, something bumped when i did the timing set.
Any help would be appreciated.

[bmdubya1198]

Are there any codes still showing? I know you replaced it already, but this sounds like an ECT sensor issue.
The evap purge valve won't affect startup. It will throw a code if it's bad, but it won't prevent the car from starting.

Did you just clean the IACV or did you replace it? It might still be bad, and it could have gotten something stuck in it. That could also cause the high rev startup you mentioned.

[98v70t5mgonegray]

I did replace the iac, ive unplugged it running and rpms went way up, kicked on a/c, it is moving for sure.
No codes, i have a basic scanner shows no fault codes no mil lamp on.
Did replace the ect, it made no change, gauge always worked fine, fans cycle on and off.
All seems the same with the new ect as well.

[mrbrian200]

First double/triple check your timing belt. Trouble starting when hot is a known issue if it's one tooth off on either the intake or exhaust cam (most vehicles, not just Volvos). If that's ok,

Also consider a cam and/or crank sensor can act like this when they're on their way out. These are hall effect sensors that utilize a permanent magnet. Magnet loses flux over time. In addition, all permanent magnets also lose strength as a function of heat, so heat soak aggravates the condition. At higher rpms (running) things are moving fast enough to generate a useable signal. Very low rpms, such as when cranking, the sensor doesn't generate enough of a voltage differential for the ECU to read and determine proper timing.

The occasional stumble at idle if not attributed to a bad ignition coil or injector I would consider a telltale sign that the signal from one of these hall effect sensors might be getting weak. They don't always trip a DTC when the ecu sees a useable signal while running, or it thinks it sees a signal while cranking (but it's weak and ignition timing is off).

Also with regard to a possible leaky injector: An most vehicles, and I doubt Volvo would be an exception to the rule, if you hold the accelerator pedal all the way to the floor while cranking this is 'clear flood mode' the ECU shuts off the injectors with the throttle plate all the way open. If it starts after trying this then you have a bad injector that is leaking when hot.

[98v70t5mgonegray]

Thanks Mrbrian200,
I'll pull it in and re-check the timing marks, considering its the last thing i did before the issue started its really a place i should have back tracked from, but having done several before and actually using an ipd cam lock tool, i figured i was golden. I'll give it another good look.
I have just replaced the crank and cam sensors, so they shouldnt be weak.
I'll give the wot a shot if timing marks are where they are supposed to be, and report back.

[mrbrian200]

I have just replaced the crank and cam sensors, so they shouldnt be weak.

Ah ha.
Try unplugging them and squirt the sensor contacts and the plug contacts with QD electrical cleaner.

A terminal inside the one of the plugs may be a little 'wide' and loosing contact with the sensor as the terminal heats up and expands. Especially if the spades on the original sensor were a little thicker than the replacement. Jumping 30 years between an original part and a replacement this sort of thing can happen.

Also, though rare, it is possible for a replacement sensor to fail prematurely.
I'm not sure how much 'detail' you would see with OBD-I tools as for gauging the signal quality of these sensors. On a '98 you might need an scope to look at that.

[98v70t5mgonegray]

Thanks mrbrian200, good suggestions for sure. I was hoping to find i had screwed up the timing belt, but i was able to check it this afternoon, all 3 marks just where they should be.
Ill grab some di-electric grease and hit the cam,crank, and ect. To be specific I replaced those after the problem started.

[darrylrobert]

Any update? sounds very much what my xc70 is doing....reading these forums can be like a good book with the last page missing..

[erikv11]

Heat soak no start is basically always going to be electrical item, if that is any help ... electrical part is failing, e.g. corroded wire or element, so it heats up under use then the resistance goes up with the heat, at startup it can't pass enough current, no start.

Not a corroded battery cable issue (those are common) if it is cranking fine. On this one I would probably suggest to look at the cam and crank sensor connectors, maybe the ECT sensor connector, no indication in the storyline the connectors were inspected carefully, except the last post suggested OP was going to look there next.

[scot850]

ECT sensor or it's wiring/connector on the power steering pump. Check the wiring carefully.

Neil.