I'm wondering if anyone knows what the acceptable rate of fuel pressure drop is for the 4.2 SV8; I am trying to confirm a suspected injector leak, having had the injectors professionally cleaned whilst the engine was out of the vehicle and now experiencing starting difficulty that was not there before.
I tapped into the fuel feed line at the filter, using a second filter to insert into the bayonet fitting and a short length of flexible fuel hose between the two filters and a pressure gauge teed into that hose. I had limited time last night but these are the results of a quickie test:
The pressure with the engine running was 55psi, which I believe is correct. Upon switching off the engine, the pressure dropped to 40psi in 3 minutes, 35psi after 5 minutes and 32psi at 8 minutes.
A second test with the line to the engine clamped off resulted in a drop to 47.5psi in 3 minutes and then almost imperceptible movement of the gauge.
A third test, leaving the gauge in place for several hours (no clamp) had the gauge drop to about 10psi.
I think that the big difference in rate of pressure drop with the line to the injectors clamped off confirms an injector leak, which is consistent with the start problem I'm experiencing. If anyone has the actual specs, or knows where I can access them, that would be great.

 

In theory it shouldn't really drop much below about 32psi, so its ready to start next time.

After driving it, does it start right away when sitting for about 10 -15 minutes?
After sitting for hour or more, does it have extended crank time before starting?

Have you looked at the spark plugs, are they wet after it has sat?

I had a customer who did the same thing, took the injectors out to have them cleaned, etc. and started having this same problem. Checked fuel pressure, etc. Letting it sit for about 15 minutes it starts right away. Let it sit for about 2 hours, long crank before starting. Replaced injectors, solved the issue.

 

Yes that is pretty much what it is doing, it will start easily enough after sitting for a short time but if it sits for more than about 20 minutes it is hard to start and gives off a cloud of black petrol-smelling exhaust smoke- presumably from the fuel that has leaked into the cylinder and results in a rich start in addition to the low fuel pressure- and if it sits overnight it is just plain slow to start- presumably from the low pressure but the leaked fuel is no longer in the cylinder. It all makes perfect sense in a most annoying way, means I'll have to remove the engine again and replace the damn injectors. Thanks for your reply that helps confirm my suspicion.

 

Smoke from petrol will be white (black is oil) and fuel pressure should come straight back up with ignition on if the pump is OK. Have you checked the pressure while it is cranking?
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Start at 8:00 mark. Not saying the guy is right or wrong but his reasoning can be a reference point to help you out.


Would cleaning the injectors damage them, on this car anything is possible because they intentionally design parts to not to be able to be refurbished or replaced from the aftermarket. I would hope that the guy cleaning them could see on the bench any problems and report back to you. If any were sticking open, that can even be caused by a brittle wiring fault on reassembly, but it would idle horribly not just cranking too long.
For the fuel pressure regulator, worth ops checking the rail O-ring, vacuum line and plug there after reassembly.
If it is really the fuel pump, that would be a strange coincidence by happening at the same time as your overhaul. But actually these cars were designed for the pump to use fuel as coolant, which means never being below quarter tank is part of owning this damn car, especially in hotter climate. So if the fuel level was very low in preparation for the overhaul, which is the reasonable thing to do normally, the pump could have killed itself, because that's what they do.

 

Thanks for your input however I don't think that is correct Kansanbrit, smoke from a rich mixture will be black, burning oil will produce blue or white smoke; I suspect that your massive injector flooding that put 15 litres into your sump caused oil to be burned, combined with a lot of unburned fuel out the exhaust. A very rich mixture, such as I'm suspecting is happening from a small amount of excess fuel sitting in the intake port or combustion chamber prior to starting, is consistent with the brief burst of black smoke I'm getting when the car has sat for a while. Leaking valve stem seals generally cause clouds of white or bluish smoke when taking off from traffic lights etc as oil is drawn past the seals under vacuum as the car slows down.
I'm not dismissing your comments, I'm building an assessment with all the info I'm getting here and elsewhere so thanks again.

Thanks for taking the time to post the link and comments. The video you posted is great info. This engine doesn't have a fuel pressure regulator like the corvette in the video, there's an electronic sensor on the fuel rail and the pump recirculates fuel inside the tank along with a complicated valve arrangement that maintains pressure. What I had thought was a fuel reg return line next to the feed line is actually the vapour line for the evaporative emission system.
I don't have much confidence in the guy who cleaned the injectors unfortunately, he was surly and unhelpful but got the job as he's the only shop in the area with the equipment. I'm also philosophical about the fact that I have no comeback on him at all, I handed him a bunch of injectors, he handed them back to me a few days later and could rightly claim he had no control over what I did with them thereafter. I don't think I'm even going to waste time by going back to him for a discussion. My trusted mechanic who suggested the leaking injectors explained that cleaning them can cause tiny particles to be dislodged but not removed, they then end up stuck downstream in the injector and prevent it fully closing.
I don't think I understand your comment about brittle wiring on reassembly, could you explain please?
An injector leak is still the lead hypothesis at this stage, although it must be a tiny leak as the car is idling ok and driving well once started. I guess it doesn't take much volume loss to lose a lot of pressure, the lines are rigid and fuel of course is not compressible. I should be able to spend some more time on a pressure test either tomorrow before I start my night shifts or next week on days off. Some have suggested that I drive it hard for a while to maximise fuel flow and see if I can wash any tiny obstruction through the injectors but I think the spray nozzles, downstream of the needle valve, are microscopic so that would probably not be a real solution.

 

If you had an injector stuck open wouldn't the pressure drop to complete zero very quickly?
I had one stuck open recently on a little four cylinder, ran really rough, tapped all the injectors with a wrench and it started to run fine.

 

 

The hypothesis at the moment is that there is a tiny speck of foreign material causing the injector valve to not seal completely when closed, as opposed to being stuck wide open as in your example and in the video. I've been informed of this exact thing happening on other vehicles after ultrasonic cleaning of injectors. If I can disprove it I'll be very happy (unless I'm up for a new pump and valve etc!) as I'm looking at engine removal, $1500 worth of new injectors and a couple of hundred $ in gaskets that are less than a thousand kilometers old. Plus an a/c regas again! And no certainty of a fix until it's all done!! So I'm very open to other possibilities. If only the injectors were staring me in the face when I open the hood like in that video. Even pulling spark plugs to look in the cylinders is an undertaking on this car. Think I'll do that first though. The fuel pressure test I did that showed a slow drop on the engine side is really pushing me toward the above theory though.

 

OK, you seem to have all the answers so good luck

 

I'm thinking I should have applied your signature line to the injectors when I decided to get them cleaned.

 

A follow-up to this- I replaced all the fuel injectors, which of course involved removing the engine again and stripping the induction system, and the problem is now fixed. Before removing the engine, I let the car sit for a while and then did a cold start. When I pulled them, 6 out of 8 injectors were wet at the tip and the spark plugs wet with fuel. I have driven the car over the weekend with numerous hot and cold starts and it is performing faultlessly so- touch wood- problem found and fixed.
I have just dropped the car into the auto electrician to re-re-charge the air-conditioning; he told me he had exactly the same experience with his own nissan patrol a while back. The problem seems reasonably common. Had I only known.

 

Thank you for the update and sharing the process with pictures. If I was facing overhauling the top end, I would also choose to pull the whole thing and cleaning the injectors was the reasonable thing to do on a list of while in there. It could have been anything, as disturbing all those connections introduces a lot of unknowns. Especially without diagnostics, this was like flying blind.

Anyway the theme with this car continues, and that it is that it demands new OEM-only replacements for the most part. What injectors did you end up going with, out of curiosity. The OEM were a hefty sum when I checked, but I also see tons of these remanufactured ones and wondering if they would be good enough. Searched for AJ811177.

https://www.ebay.com/itm/201820425788
https://www.ebay.com/itm/303330672795

 

I bought new Denso injectors from British Parts UK. I did see a multitude of refurbished options such as the ones listed above, but the work involved in accessing them really meant that new was the only option in my mind and the idea of an ebay purchase made me nervous. It is a sweet relief to have the car running properly after all that work, a box of matches was not far down the list of options if it hadn't worked.

 

Glad you figured it out mate. I have the skills but have not yet done the research - why/how are the injectors/rails not accessible while the motor is in the vehicle?