Q45/1994: Flooding. Help validate...

[Mint Q45A]

Hello...I need some help with the following:

Background and symptoms: - A few months back the car began having slight/sporadic issues when starting first thing in the morning. It would cough a little, and I would need to crank it probably twice. This would only happen in the morning. After that the car would run (and still does) perfectly; no issues re-starting during the day. Strong performance; smooth idle...- The frequency of these symptoms seemed to have gradually increased in the last few weeks- Last week did the required Emissions Testing - everything came out ok; very good numbers, way below the limits- In the last couple of days the symptoms have turned worse; now it looks looks like a "flooding" situation. I have recurred to the process of pressing the gas pedal at WOT before and during starting so that the ECU doesn't open the injectors- As soon as it starts, a big, smelly (fuel), cloud of smoke comes out the exhaust- Again, no issues during the day; car runs and re-starts, perfectly.- This only happens when the car sits overnight (garaged, but ambient temp dropping into the mid to upper 30's)

Other info: - 122k miles- New fuel pump installed very recently- Resisitance for all injectors (measured at the harness) within 12 to 13 Ohms range- TB and IAC cleaned recently - suspecting that these had something to do with the sporadic hard starts- Plugs replaced less than a year ago- Original injectors, except for two, replaced approx. 60k miles ago

Theory (and here is where I need help):- Considering that the injectors' resistance is ok, I suspect that one or more "O" rings have deteriorated and are letting fuel sip through into the cylinder(s)- The issue is more relevant now, with colder outside temps; any fuel that sips into the cylinder during the night will not evaporate, causing the flooding situation.

- Is it relatively common for the injectors' O rings to fail?- If this is the case, does Joe T sell them? As a kit?- Should they all be replaced? - Or is there something else that could cause the flooding?

Note: No fuel smell inside the engine compartment; valley under the plenum is completely dry.

Plan: - Do a leakdown test - From what I understand this consists of installing a pressure gauge between the fuel filter and the fuel rail. Pressurize the rail by opening the ignition and letting the FP build the pressure. Apply some sort of hose clamp to the fuel line (before the gauge) as well as to the return line to hold the pressure. Watch the gauge for any pressure drop over a period of time.

Questions: Is this the correct way to do this type of test? What kind of pressure drop vs. time is considered acceptable?Can you use compressed air instead of fuel to pressurize the fuel rail? Assuming the test is positive (there's a pressure leak), what is the best way to identify the injector(s) that need the new O rings? Remove the plugs? Remove the whole fuel rails with the injectors and run another test, outside the car?

Tks in advance for any help or suggestions you can provide me.

In the meantime I plan on removing the fuse to the fuel pump as soon as I park the car at night (while it is still running) and let it go dry. Then remove the fuel line feeding the fuel rails.... I just don't want to run the risk of hydrolocking and causing some severe damage....

Does this make sense?

[Q45tech]

Tee in a fuel pressure gauge and using a special clamp tool/wrench block off fuel return line and watch and graph the pressure vs time................it should drop to 34 psi and even overnight not go below 20 psi..................leaks in rails/injectors are the only place it can go..........unless FP check valve is failing or you haven't fully blocked off return line.

About every 6-7 years I've rebuilt my fuel rail hoses but never had to replace a FI o-ring.

With ethanol the rubber o rings can swell and leak -- self inflicted damage.

[Mint Q45A]

Q45Tech (Dennis?),

Tks for your feedback. I will try to do the leakdown test in the next couple of days

Based on the symptoms I described, could there be any other cause for the flooding - besides the potential rail/injectors leaks?

Note: I checked for any voltage readings on the connector coming from the ECU to the injectors, with the car off. Nothing = Good. This was just in case that for some strange reason the ECU was signaling the injectors to stay open, even after the car had shut down....

[Q45tech]

A major reason things are designed to ground [go to low resistance to ground] to operate is that when transistors fail they usually blow open like a fuse to protect against running when off.

Think: injectors, ignition coils, hvac fan controller, etc.

The transistors are sized so that 100% duty cycle will blow them open eventually as they overheat.

Maximum duty cycle [dwell] on injectors [coil] is about 55% of time open/energized.

Never seen a shorted working injector driver transistor..

I would look at coolant temp sensor and make sure the resistance tracks with FSM vs temperature as this sets the time the injectors are sequentially open, then following that the extra richness after crank................the higher the resistance the more fuel per time period.

[sdkhalsa]

This sounds very much like a situation(white cloud included) I had with my 94' Q which was so bad as to make the car not drivable. Half of my injectors at the time were just over a year old with half about eight months old. I pulled all of the injectors and had them tested by an excellent shop here in Phoenix -- they were all OK. The conclusion that I and the shop owner reached was that one of the o-rings failed. This was after more than six months following installation.

Perhaps the problem was accidentally reusing one of my old o-rings, but just to make sure I changed all of the o-rings, and became super meticulous in lubricating and installing them. Some people on the site go to the trouble of pulling the fuel injector holders and have the injectors installed by an injector shop followed by a pressure check. This seems a bit over-the-top to me, but the time required to open the plenum and repeat the job could well justify the effort. I would highly recommend changing the short sections of fuel hose when doing the injectors as they are very difficult to get at otherwise. One of mine started leaking at 110 K and it was a real bear to get at.

[Mint Q45A]

I will look into the Temp sensor, although considering that the issue is when the car is absolutely cold, I am not sure it could be affecting much.

I plan on pulling the fuel rails (the whole assembly) with the injectors still on (assuming these come off the intake manifold relatively easy - I guess there's an o-ring on each injector) and then tun the fuel pump on to check for leaks.

Question: Do the gaskets on the runners get damaged when the plenum is removed or can they be reused?

[goody90q45]

I plan on pulling the fuel rails (the whole assembly) with the injectors still on (assuming these come off the intake manifold relatively easy - I guess there's an o-ring on each injector) and then tun the fuel pump on to check for leaks.

That's a lot of work just to check for a leaky injector. Do the 20 minute job first (leakdown test) and then think about pulling the plenum. If you're lucky it might be #1, #2 or #8 fuel injector leaking in which case you wouldn't have to pull the plenum. I think you hooked up with Jay at a meet. Why don't you see if he or one of the locals can hook you up to NissanDataScan and figure out which fuel injector is leaking.

I'm feeling your grief because I'm having the same problem now that the weather has turned a bit cooler (NorCal). It takes an extra 1/2 second to start in the morning and then it's rough for the first 20 seconds of warmup with a minor fuel smell (exhaust?). After that, fine all day. Gas mileage is down about 1 mpg. I'll be doing the leakdown test myself in the next couple of weeks. I also should add that I had o-ring failure on 2 different injectors early in ownership, both resulting in hydrolock, with no engine damage. I inherited these problems from the previous owner I believe.

Question: Do the gaskets on the runners get damaged when the plenum is removed or can they be reused?

If you're talking about the gaskets between the plenum and the intake runners.... I had new ones available when I removed my plenum to replace an injector and when I compared old to new there was little difference so I ended up reusing the old gaskets. I depends what condition they're in (brittle / supple?) and if you mind spending the hour or two to loosen the plenum again if you guess wrong. I'd be more worried about the hoses attached to the TB and IAC and whether I'd be able to quickly find a replacement if one cracks.

My experience is you can get a pretty good idea of what shape the under plenum hoses and gaskets are going to be in just by feeling a couple of accessible hoses near but above the plenum. Are they supple or do they crack when you squeeze or bend them? My Q was supple or I wouldn't have removed the plenum but I parted out one where the hoses crumbled like cold peanut brittle.

It's your call as to how many new parts you want to have on hand when you remove the plenum. You've read enough posts to know that many on this board would recommend replacing everything.

[Mint Q45A]

Mike,Tks for the feedback. This is very good info.

I just finished setting up the leakdown test. After the first 30 min I already saw a 5 psi pressure drop (from 40 to 35). I will be monitoring the pressure every 30 min for a couple of hours and check it again tomorrow morning. The hard part is knowing whether the return line is completely close/blocked or not; I just clamped....

Note: I will email you a photo illustrating the "setup"

Depending on the results I will decide whether to remove the plenum or not. Fortunately, based on my recent experience cleaning the TB (had to remove it completely to replace when replacing the VC gaskets), as well as the IAC valve, the hoses are not brittle. But that doesn't mean I probably will not end up needing to replace more parts.

Is the NissanDataScan able to pinpoint exactly which (if any) injector is leaking?

[3Q Jay]

one other ting to consider.....if you start with a 'hot' rail or even warm, you will see pressure drop as the gas/vapor cools following shut down.

so, best way to do the leak down is on cold engine, turn key on, let pressure come up, then key off and watch the decay.

also note that with key ON engine OFF, there will be no vacc signal to the pressure regulator on the ds rail, and you will get ~45psi.

[Mint Q45A]

Jay,Good to know. After 75min, the pressure has already dropped 15 psi (from 40 to 25). I did start the test with a warm/hot engine. Considering your feedback, tomorrow morning I will re-start the test, with a cold engine and leave the gauge on during the day - but I will also re-tighten the clamp on the return line, just in case.Tks!

[Mint Q45A]

After just 1.5 hrs the pressure had already dropped 20 psi...

I am restarting the test: Now the engine is cold, and I am using a sturdier clamp on the return line; but I am also clamping the line from the pump, just in case.

[Q45tech]

You could just use a section of hose with a bolt screwed into it to replace the return line avoiding a clamp to stop flow.

34>20 psi is only 24% less flow from injector for the same opening time. Note that ecu adjust opening time to match battery voltage to injector and coolant temp sensor supplies addition data to lengthen open time during cranking and warm up phase.

Have seen corroded coolant temp sensor connectors create additional cold resistance make ecu think it's below zero when it was actually 40F

[goody90q45]

Mike,Tks for the feedback. This is very good info......Note: I will email you a photo illustrating the "setup"

I got your pics and will post them up tonight.

Is the NissanDataScan able to pinpoint exactly which (if any) injector is leaking?

With NDS installed on your laptop you can turn off one cylinder at a time. From there you can determine in which cylinder you feel the least change to help zero in on the leaker.

[Mint Q45A]

The results are in....- 5 psi press drop in the first half hour - similar to what I saw before. Went to bed...- This morning: 40 psi press drop (zero pressure on the gauge!).I thought of the "hose+bolt" idea for the return line, but couldn't risk spilling gas in the garage - the previous night I did spill some gas, the fumes got into the house and wife was going to kill me...... Now that I have Zero pressure in the rails, I will do it and run one more (and last) test...

If I get similar results, the plenum is coming off.....

In order to identify the leaking injector(s) I thought of the following options: - "Sniff test" : once I remove the plenum, I expect to get a stronger gasoline odor from the runner(s) where the leak is- "Paper Towel Test" : stuck paper towels down the runners, reaching the injector area and check for any moisture (fuel). If not, run the FP and wait for the pressure to drop - check the towels again- Pull the whole fuel rails assembly and run the FP - this is my last option...

Dennis, is it correct to assume that if the injector's resistance is ok, the only chance for it to leak fuel is through the O-rings? In other words, no need to replace the injector?

Unscheduled oil change comming up...

Tks!

[Q45tech]

The solenoid [coil resistance] that surronds the pintle has nothing to do with leaks! Internally a spring holds the pintle closed.

Now dirt or deposits on pintle can wear the socket or keep it from closing properly.

Temperature changes sound like hoses or gaskets.

There is a check valve on pump to keep the pressure from reversing the pump.

I've never tested the fuel pressure dampener to see exactly what it does other than react to WOT high air flow in MAF....................

It might be useful to crimp fuel line before gauge to confirm which way the leak occurs to rule out pump backflow.

[Mint Q45A]

Dennis,

Ref - Crimp the line from the filter to the gauge to rule out fuel backflow...

I thought about it and that's how I set it up (big, heavy-duty clamp ) and left the test running, one more time - hopefully the last... (using the hose+bolt+clamp on the return line too).I will see the results when I get back home later today.

Tks for your feedback about the potential causes of leaks from the injectors!

Mike, I will be sending you new/better pictures with the "final" setup...

[goody90q45]

Dennis, Ref - Crimp the line from the filter to the gauge to rule out fuel backflow...

Mike, I will be sending you new/better pictures with the "final" setup...

Here's a couple of pics sent to me by MintQ45a showing his gauge and clamp set up for measuring fuel pressure drop. Should I be looking for a gauge to measure liquid pressure or can I get by with an air pressure gauge?

[Mint Q45A]

Ok, here is the final result....

After using the setup shown on the pictures (Goody, tks for posting them for me): completely blocking the return line with the bolt + hose + clamp, and adding the heavy clamp on the line from the filter to the gauge and letting it sit for almost 12 hrs...: No pressure drop, at all.....

This means the injectors/rails are Ok...

Lessons learned: - Need to tight the clamps really hard- The fuel pump seems to allow some backflow (although is new), therefore it is better to clamp it. As a matter of fact, when I was done and I removed this (orange) clamp, the pressure dropped approx. 10 psi, meaning that the line from the pump to the filter had already lost some pressure. - After a couple of failed attempts/false readings, finally learned how to do the test, correctly

NOTE: I used a cheap tire gauge I already had + a $2.00 nylon T fitting (from ACE hardware) and some fuel hose and clamps

One quick tip- After completing the test: Remove the clamp from the feed line, remove the fuse for the FP, start the car - it will barely start and die. This way you remove all the pressure from the rails; you can then remove the gauge and reconnect everything back...all without spilling any fuel. Finally put the fuse back on, and you are done...

Hope this is helpful

As far as the flooding, I am not sure...I now suspect that my temporary fix for the dead KS (using the 500kOhm resistors) have something to do. with it..therefore I will be replacing the KS+harness...They are already on their way from Joe (with some injector O-rings that I won't need...)