Can these cars vapor lock? 1998 V70 T5 Topic is solved

[S Carlson]

It's been very hot in Massachusetts this past week. I am seeing the effects of this extreme heat in a number of ways. Monday, after commuting from work to daycare (about half an hour) in 90 degree heat, and parking for about 15 minutes to pick up the kid, I went to start the V70. It cranked, sputtered, and did not start. When I tried to start a second time, I just cranked and cranked with no sputtering, nothing at all, just cranking. I waited a minute, tried again. Same thing. I waited a few minutes. I cranked again, and the car miraculously started. Phew! Drove to a house we were looking at (turned out to be way over our budget) and after that the car worked fine the rest of the week.

Took the family camping this weekend. Drove all over to lakes and ocean and ice cream stands, temps in the 90s. On our way home, we stopped at a supermarket after driving about an hour and a half. Was in the supermarket about half an hour. Came out. Car again cranked, sputtered, and did not start. Cranked again and got nothing. Tried waiting a minute and cranking. Nothing. So I opened the hood and spritzed some fuel from the Schrader valve on the rail, just to check fuel, even though I recently did the fuel pump relay and fuel pump. It seemed like half of what came out was vapor! I spritzed some more until it was mostly liquid (or at least seemed that way). Got back in the car and it started right up!

Fuel injected cars can't vapor lock, can they? CAN THEY??? Most fuel injection systems have a return line, so fresh fuel is circulating and would flush any vapor back into the tank, so they shouldn't be able to vapor lock unless it's right in the rail.
BUT. This is the 98 V70, with the fuel pressure regulator down by the steering rack. There's a single line that goes 3 feet or so up to the engine. That line is a one way street. I can imagine, sitting parked with the engine very hot from an hour and a half of driving on a hot day and then sitting on hot blacktop (and possibly leaky injectors lowering the pressure in the line), the fuel in that line could vaporize and the engine would not start.

Does this seem plausible? Or am I a crackpot for even theorizing this?

[Grantkat]

You you could be suffering from fuel delivery or venting issues that mimic the symptoms of vapor lock. Though anything is possible, true vapor lock is extremely rare for an EFI system as opposed to a carburetor, the high-pressure fuel continuously circulating from the tank keeps the fuel system relatively cool.

here are a few suggestions to look at:
1) Malfunctioning EVAP system, which controls fuel tank vapors. If the EVAP purge valve gets stuck or the charcoal canister becomes clogged, fuel vapors cannot properly cycle, leading to a pressurized/vacuumpacked tank and hot-running issues or stalling.

2) A failing fuel pump - As the pump wears out, it struggles to maintain the correct line pressure, resulting in stumbling or stalling.

3) If the fuel pressure regulator diaphragm fails, it can flood the engine with excess fuel or allow fuel to drain back into the tank, making the car hard to start when it is warm.

4) Clogged fuel filter

5) Fuel tank venting - open your fuel cap. if you hear a loud rush of air, your fuel system isnt venting properly.

these are more of a catch-all to eliminate potential issues and try to narrown down the culprit

[abscate]

Add the fuel pump controller ( ‘ fuel pump relay’ ) to this list of checks, they fail in both hot and cold modes

Don’t use aftermarket for that part

[S Carlson]

Did you read my post? I mentioned recently changing pump and relay, plus lots of pressure at the rail. I realize it was long, but the information was in there, multiple times.

As I mentioned above, these 1998 x70 cars are not typical efi systems, because the fuel pressure regulator is not right at the rail. Instead, there is a single line to the rail from the fpr which is hanging down by the steering rack. This line is a one way street to the fuel rail. Fuel is not constantly circulated in this line, so fuel could vaporize in it, especially if the injectors leak down enough to drop the pressure.

In response to the possibly-chatgpt-generated list:

1. The evap system is not going to affect fuel delivery. That's a crazy notion. The fuel pump operates at pressures far exceeding any fluctuations in the tank. But since you asked, the evap system is fine.

2. As I stated above, fuel system is healthy. Pump is new. Fuel pump relay has been rebuilt with new caps and reflowing solder joints. Fuel pressure at the rail was high when I checked, but seemed to mostly be vapor at least at first. I also recently checked fuel pressure with a gauge.

3. I've checked the fpr vac line. No evidence of fuel in there so I think we can rule out a blown fpr diaphragm.

4. Just changed the fuel filter.

5. Not happening. Again, evap system is fine. Plus, at the risk of belaboring the point, I fail to see how a small pressure differential in the tank could cause a no-start plus vapor in the fuel rail.

I just want to know if anyone's heard of it happening, where fuel vaporizes in that three-foot one-way line from the remotely mounted fpr to the engine. We have had this car since 2013, but we don't drive a lot. Others may drive more and might have seen something like this. I see a lot of unresolved threads about intermittent crank-no-start on these forums (user rebecca8 among others), but no definitive answers are forthcoming. Still, I'm up to date on the usual maintenance (plugs (NGK), wires (Bougicord), cap, rotor, pump, relay, fuel filter, pcv, and many other things) and I am familiar with this car.

[abscate]

Sorry I missed the relay and pump replacement line. If you used Volvo parts I would rule those out

These cars never vapor lock in my experience. Check fuel pressure at the rail when the no start occurs to rule that out. At spec pressure , that fuel line would have to reach 80-85C to boil the gas inside. I doubt that is happening

[Clemens]

Did you read my post? I mentioned recently changing pump and relay, plus lots of pressure at the rail. I realize it was long, but the information was in there, multiple times.

In response to the possibly-chatgpt-generated list:

Not exactly the tone we appreciate here at MattewsVolvoSite. Just saying ...

[Grantkat]

Did you read my post? I mentioned recently changing pump and relay, plus lots of pressure at the rail. I realize it was long, but the information was in there, multiple times.

As I mentioned above, these 1998 x70 cars are not typical efi systems, because the fuel pressure regulator is not right at the rail. Instead, there is a single line to the rail from the fpr which is hanging down by the steering rack. This line is a one way street to the fuel rail. Fuel is not constantly circulated in this line, so fuel could vaporize in it, especially if the injectors leak down enough to drop the pressure.

In response to the possibly-chatgpt-generated list:

1. The evap system is not going to affect fuel delivery. That's a crazy notion. The fuel pump operates at pressures far exceeding any fluctuations in the tank. But since you asked, the evap system is fine.

2. As I stated above, fuel system is healthy. Pump is new. Fuel pump relay has been rebuilt with new caps and reflowing solder joints. Fuel pressure at the rail was high when I checked, but seemed to mostly be vapor at least at first. I also recently checked fuel pressure with a gauge.

3. I've checked the fpr vac line. No evidence of fuel in there so I think we can rule out a blown fpr diaphragm.

4. Just changed the fuel filter.

5. Not happening. Again, evap system is fine. Plus, at the risk of belaboring the point, I fail to see how a small pressure differential in the tank could cause a no-start plus vapor in the fuel rail.

I just want to know if anyone's heard of it happening, where fuel vaporizes in that three-foot one-way line from the remotely mounted fpr to the engine. We have had this car since 2013, but we don't drive a lot. Others may drive more and might have seen something like this. I see a lot of unresolved threads about intermittent crank-no-start on these forums (user rebecca8 among others), but no definitive answers are forthcoming. Still, I'm up to date on the usual maintenance (plugs (NGK), wires (Bougicord), cap, rotor, pump, relay, fuel filter, pcv, and many other things) and I am familiar with this car.

Hey There S Carlson,

Not Chatgpt, though interestingly I checked and it came up with a similar list (not bad for generic AI). Those came directly from an indy mechanic I know. I see you eliminated evap. thats all good.
You are correct, evap doesnt affect fuel pressure However, a malfunctioning evap does have the potenial to affect fuel/air ratios. Not a given by any means, however again that was an attempt to look at anything which might might be a contributor.

[abscate]

On the return lacking fuel system , used in 1998 1999, the evap pressure does control fuel pressure. This posters 1998 does not use this system though, as he’d has identified the FPR on the rail

[S Carlson]

Sorry I missed the relay and pump replacement line. If you used Volvo parts I would rule those out

I'm sorry, I probably came off as rude. I was trying to get the dang thing fixed. We have a toddler screaming at us and another baby due any day, in addition to full time jobs. My wife has given a vote of no confidence in this car, and begs me to get her a Prius, which I will probably have to do.

I replaced the pump with a Walbro, which after using them on track cars I consider equal to or better than OE, and I rebuilt my own relay, because I rebuild electronic MRI and NMR components for a living, so a relay was child's play. I used good Nichicon caps and I can hear the fuel pump prime, reliably, when I turn the key. That's another advantage of the Walbro, you can definitely hear it when it runs!

These cars never vapor lock in my experience. Check fuel pressure at the rail when the no start occurs to rule that out. At spec pressure , that fuel line would have to reach 80-85C to boil the gas inside. I doubt that is happening

As a quick and dirty pressure check, I spritzed fuel from the Schrader. I haven't yet found a pressure gauge that doesn't leak when I attach it at the Schrader, and that's not for lack of trying. I ended up just buying and installing the Walbro pump and rebuilding my relay for peace of mind. However, with a lot of PTFE tape I was able to attach one with only a small drip and got the spec pressure, no problem. My hypothesis was that an injector was leaking down a little when the car was shut off, reducing the pressure just enough for vapor to form on a very hot day. The engine is pretty dang hot. Too hot to touch, and remember I solder for a living, so I touch a lot of hot things. The top of the engine hits upwards 70C for sure, after running in traffic during the 100 degree days we've been having. Plus that line goes right past the exhaust/turbo. It is a hot house in there. That and the one way fuel line for 3ft after the regulator, which is above the steering rack, was why I considered vapor lock a serious possibility.

On the return lacking fuel system , used in 1998 1999, the evap pressure does control fuel pressure. This posters 1998 does not use this system though, as he’d has identified the FPR on the rail

Not on the rail, but about 3 feet back, kind of dangling over the steering rack. It is a bizarre location for the FPR if you ask me. I would retrofit to a design with it on the rail, if it exists. Does it exist, in the older 850s? I have a pressure dampener on the rail as well.

=======================================

That all said, I think I found the actual hot start culprit. The cam position sensor was full of oil due to failed cam seals. I was not getting the EFI 314 code (P0340) until I got it to sputter/start and run very badly by holding down the gas pedal. Typical taciturn Swede prefers to suffer in silence. But after getting the car to run badly, let up on the gas and the engine stalled, and then restarted and ran perfectly. But I had the historic fault code P0340. That is what tipped me off to the cam sensor. The seals basically came out in my hand, and were very crispy. I did the glove test to verify that PCV was still working (R&R'd that whole system in 2020 only 30k miles ago), and checked the cam seals on the timing side of the engine, which seem still fine (phew!).

It is interesting that Motronic4.4 doesn't seem to care if the cam position sensor is failing while the car is running. I think it must rely on the crank position sensor once it's running, but needs to figure out the cam position when starting, because the cam could be in one of two positions for any position of the crank. Once it's running, my hypothesis is that it keeps count of the crank revolutions and doesn't need the cam sensor unless it loses count. On the older Saabs and Hondas I am used to working with, there's only the cam sensor, so when it exhibits temperature dependent malfunction, the engine quits while you are driving and you have to wait for it to cool down before you can drive some more. Late 1990s Saabs had the coolest system, where they figured out where the cams were at by sensing capacitance across the spark plug gaps! Then they only needed a crank sensor! However, the capacitive sensing system would also die in the heat.

My initial thoughts of vapor lock may have come from spritzing the fuel Schrader (initially to check pressure), which involved opening the hood, and that and spraying fuel might have cooled the sensor down just enough to let it work again to start the engine. After getting the P0340 code, I experimented with pouring water on the cam sensor to get it to start. That seems to work as well. So now it's got new seals, new sensor, and a new distributor rotor (because those have that resistor that can fail in heat as well) and hopefully we are good. And we are headed into the jaws of an El Nino summer. Baby is due any day. Wish me luck!

[matthew1]

Thanks for posting the follow up. Good luck with your new kid and current kid. Teach em young!

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