98 S70 T5 - no fuel pressure

[shegarty]

I have attempted to get a pressure reading but the tester that I was able to find was not useful. There wasn't enough room between the valve and the throttle cable assembly to connect the 90deg attachment. I tried using an adapter and some fuel hose but was unable to get an accurate reading. I will see what I can pick up tomorrow. When I say that there is no fuel pressure after 24hrs I mean that the line is totally devoid of fuel, we are talking about a big leak-down somewhere. When I installed the fuel pump after the car had been sitting for about 24hrs and there was no fuel at all in the output or return lines when I disconnected them.

[RickHaleParker]

Should I find a leaky injector does anyone have a set of whites for sale???

I would go to eBay and get a set of remanufactured injectors that are flow matched with tight specs.
Remanufactured are just as good as new. Flow matching increases performance and fuel economy.

Flow matched will cost you more up front but with the fuel economy increase, in time they will pay for themselves. Making flow matched an investment with dividends, not an additional expense.

[shegarty]

Get a fuel gauge on that valve and get some real measurements

It’s normal for pressure to be gone overnight, the spec is something like 50 psi and 30 psi after 20 minutes. You cannot predict pressure by how much it squirts, get some good data

Ok, with the rail off and the injectors connected I was able to finally get some readings with the pressure tester ... after priming the system by turning the key to position 2 four times here is the data:

0min - 38 psi
1min - 36 psi
5mins - 34 psi
10mins - 31 psi
15mins - 28 psi
20mins - 28 psi
30mins - 25psi

According to what I have read I think this is out of spec (10% over 20mins?) and pressure is draining too quickly through a leak in the system. All of the injectors are dry and I have already replaced the fuel pump ... fuel pressure regulator?

Also, when doing all this work I noticed that the main engine ground from the battery is corroded through, I am in the process of attempting to remedy this now by crimping a new lug ... maybe the problem is electrical?

[scot850]

For a 98 43psi is considered the minimum operating fuel pressure for the system. So if you have only 38 psi with a new pump you must have pressure leaking somewhere like you say.

Neil.

[Roger_850T]

I don't think that leakdown rate is your problem. It's reasonably slow. Keep in mind that the real reason for the check valve and keeping the system pressurized is to prevent vapor lock on a hot summer day when the car was just shut off. (It can get really hot under there, and fuel in the lines would flash into vapor. By maintaining the pressure, the fuel would have less of a tendency to vaporize in the lines, and the car would start again.)

What is supposed to happen: The fuel line can happily be all the way down to zero. When you turn on the key, (to "position II",) the ECU should turn on the relay (and thus the pump) for "a few seconds" to pressurize the line, then turns it back off again. It doesn't inject any fuel at this point, just pressurizes the line. If you are watching with a fuel pressure gauge, you should see the pressure pop up to whatever the regulator is controlling to.

The ECU won't start the pump again until it sees the engine turning. It detects this by the crank sensor (i.e. the sensor that's on the bellhousing looking at the flex plate / flywheel.) Once it sees this signal, it turns the pump back on and keeps it running until the signal goes away, which should include the time you are actively cranking the engine, then continuing once the engine starts running.

I would repeat the pressure drop over time test, but then look at the gauge when you turn the key back on to start it again. If it pops back up to where it should be, then I think all is pretty much in order there.

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Which doesn't really address your no start issue.

When you are cranking, does it sound completely dead, or like it sort of wants to run but not quite?

Things I am thinking of:
- Fuel isn't vaporizing very well when cold. Old injectors with a poor spray pattern won't help with this. Also, old gas or summer gas will have a different volatility. If the gas is relatively recent then it's probably not the issue.
- Idle Air Valve isn't moving much, or is stuck, and doesn't allow extra air when it's cold. (Does stepping a little on the gas pedal while you crank make any difference at all?)
- Temperature sensor is not reading correctly, so it's not enriching enough when it's really cold. (This is kind of a long shot, wouldn't be my first guess; I'd want to measure first before replacing.)

Thinking back to the injectors, there are places that will clean/flush your injectors for ~$20 each. I've been thinking about it - not because I have any issues, but more preventative to make sure all is good. Probably as good as, if not better than a replacement set - because then you know they've been tested and demonstrated good. (Used set might be as bad as what you already have.) A set of remanufactured ones as described above would also be fine.

Other things I think of you've already looked at - air leaks, hoses not sealing, split, cracked, etc.

Also, I'd check the ignition system is up to snuff - when it's cold, it will be hard to light off the fuel/air mixture, and a weak spark due to plugs/cap/rotor/wires/coil etc. won't help.

Does it get easier once the temp comes back up again?

Good luck! Hope this helps!

Roger

[shegarty]

For a 98 43psi is considered the minimum operating fuel pressure for the system. So if you have only 38 psi with a new pump you must have pressure leaking somewhere like you say.

Neil.

I'm not entirely sure on this as it could totally just be a calibration error - I have never used this gauge before and it was a loaner tool. I was more concerned about documenting the pressure rate drop.

[shegarty]

Roger - the fuel pressure pops back up again just as you mentioned and appears to be acting normally - does anyone else out there have an opinion about the rate of the pressure drop? There seems to be little consensus on what is "normal".

As for the other suggestions, I am using new fuel, idle air valve has been cleaned thoroughly (gas pedal depression doesn't change no start issue), ECT was replaced with a new unit about a year ago maybe along with crank and cam sensors. Plugs, wires and cap are relatively new, also tried switching out the coil for a know good unit with no change.

After finding the bad ground (main ground to battery from engine block, totally corroded through and not connected at all) I am now leaning towards that as a possible culprit maybe generating a weak spark, which would be dependent on temperature and could also get worse with time. I know that there are multiple grounds that would probably be able to handle the load of starting but under the stress of low temps they were not able to keep up to the high amperage demand of starting. For the last couple of weeks it seems like it got progressively worse without and dependence on temperature - possibly as the last of the connection corroded through?

The one thing that still confuses me - why has cycling the key to position 2 several times helped with the no start issue in the past? Also, when I was replacing the fuel pump why were both the main supply and return lines to totally empty? There wasn't even any residual fuel that spilled when I disconnected the lines.

[Roger_850T]

According to VIDA, the pressure should be 300 kPA (~45psig). For residual pressure it should not drop below 200 kPa (~30psig) in less than 20 minutes.

Technically, you are out of spec by ~2psig.

From a practical perspective, if you were telling me you were having trouble with hot start and vapor lock, it might be an issue. For your cold starting issue, I think it's fine. Especially since your pressure comes up when you turn the key on.

You might try checking for spark by pulling a plug and cranking with the plug next to the head - just to get a visual on how strong or weak the spark looks. (Fishing here.)

The ground issue is plausible, or at least something that should be fixed anyway. Usually that causes more of a "battery fails to charge" issue, as the poor ground generates a voltage drop on the ground side, and while the voltage regulator holds the voltage at the right spot, the battery doesn't see it (due to the high ground voltage drop), and it doesn't charge. Or, the car cranks slowly. You could probably test it by using a jumper cable from the battery negative to the engine block, (in parallel with the ground strap,) and see if it makes a difference.

FWIW, Volvo had an issue with some earlier (~93 or so) cars - the oil companies added more ethanol to the fuel, and it changed the volatility of the gas, (especially at low temperatures), and the ECU didn't enrichen enough for the lower volatility gas. It would start and stall out right away. They fixed that one by flashing the EPROM on the ECU. That's long enough before your '98 that I doubt it's an issue.

Roger

[Roger_850T]

What did your pressure come up to when you turned the key to II? In your test data above, it looks like maybe 38psig? That might be a little low, and might be contributing. Converting more precisely, 300kPa would be 43.5psig, so at 38 you are at ~90% of where you ought to be. That would cause it to be injecting only ~90% of the desired fuel, not quite as rich as it ought to be, especially when it's cold.

Is that the cause of your issue? Good question. Perhaps it's something that is contributing (along with other items) to the issue? Maybe that and injectors that aren't atomizing well? I don't know, just pondering here.

Roger

[shegarty]

Thanks Roger - the pressure might be a little low but the tool I am using is a loaner from the auto parts store and I have no idea when or if it has ever been calibrated. Also, if the schrader valve is not flowing 100% it might read a little low too - during normal operation pressure appears to be sufficient she pulls like a champ with no loss of power that would be associated with low pressure or badly flowing injectors.

As to running lean - it appears to be running rich if anything after hard starting but this could be due to the extra fuel present after a long cranking time. Exhaust has a definite smell of fuel for the first 30secs or so and then cleans up.

I have addressed the bad ground issue with a temporary solution of a household screw clamp connection to rule it out a possible cause.

As the issue only appears to be a problem after extended periods of time I will have to wait until the morning to see if it has any effects.