My ongoing fuel injection woes (Now with compelling HD Video)

[KDMatt]

Alright, so I've been struggling with my car since last October (more so than ever in the last month). I've been having an ongoing 'lean' condition problem.

Here are the components that were called into question and have been replaced:

Fuel Pump (brand new, tested and working within spec)

Fuel Tank (washed/recoated)

Fuel Pressure Regulator (Tested and working within spec)

Fuel Injectors (replaced approx 20,000 miles ago)

Fuel Filter (less then 5000 miles ago)

Water Temp Sensor (replaced approx 20,000 miles ago, with injectors)

Components that were/have been called into question:

Air Flow Meter (swapped with a second unit I have handy, produced the same results)

Ignition Coil (tested according to FSM, along with Ballast resistor, both seem to be within spec)

Ignition Module (no idea yet)

Dizzy Cap/Rotor

Plug Wires

Throttle Position Sensor (tested according to FSM specs and seems to be working okay)

ECU (checked solder joints, a few were a little dirty -- resoldered, same results)

Auxiliary Air Valve (Currently have it taped off/bypassed, results are only marginally improved)

Vacuum Check (low at 14.5 psi, but the car used to run just fine at this pressure)

... and that's all I can think of right about now

This morning I thought I had fiddled with it enough to try and take it for a little jaunt. I put the car into the carwash and let her sit, engine off, as the power sprayer washed off months of crud (actually got a pretty heavy dousing INSIDE the car on the driver side).

Anyway, about 1/4 mile after the carwash things got almost INTOLERABLE. It was coughing, sputtering, and backfiring worse than ever. I honestly thought it was going to peter out and die. I was very fortunate to have gotten it home.

Anyway, since the symptoms were so pronounced I quickly ran inside and grabbed the camera and shot a couple minutes of what it's doing, so hopefully I can get some other ideas about what's going on.

Something screwy is going on here.

(Oh, and before I get a million people suggesting ignition, the last time I read the plugs they were all lean .. all of them. I'll double check once I've got some daylight to work with, but I'm pretty sure they'll come back lean again, even though I haven't put many miles on the engine since changing anything).

[Zed Head]

It might be that your injectors aren't firing on every revolution like they're supposed to. That could be an ECU problem. Make sure that injectors have a 12.6 volts at the connector pins with the key On. Ideally, you would also measure voltage when running to verify current flow but that would take some ingenuity. It should drop to ~9 volts due to the dropping resistors and the injector load when running from what I've read.

Edit - I just looked back at your post and see that you've already been in the ECU. For what it's worth I had a bad ECU but could find no visible signs that it was bad. I'm pretty sure that the FSM says if you've checked everything and still have a problem, it must be the ECU. Not a very satisfying way to solve a problem though.

I've seen several stories about people kicking or bumping their ECUs to fix a problem. Usually they were fixing a rich condition though.

Edit 2 - Did you find water in the area of the ECU after the car wash? Has it been getting the occasional watering over the years? You might check the ground circuit to the ECU also. The ECU has to have a good ground to fire the injectors. You might have rusty ground points.

Edited June 22, 2011 by Zed Head

[KDMatt]

It might be that your injectors aren't firing on every revolution like they're supposed to. That could be an ECU problem. Make sure that injectors have a 12.6 volts at the connector pins with the key On. Ideally, you would also measure voltage when running to verify current flow but that would take some ingenuity. It should drop to ~9 volts due to the dropping resistors and the injector load when running from what I've read.

Edit - I just looked back at your post and see that you've already been in the ECU. For what it's worth I had a bad ECU but could find no visible signs that it was bad. I'm pretty sure that the FSM says if you've checked everything and still have a problem, it must be the ECU. Not a very satisfying way to solve a problem though.

I've seen several stories about people kicking or bumping their ECUs to fix a problem. Usually they were fixing a rich condition though.

Edit 2 - Did you find water in the area of the ECU after the car wash? Has it been getting the occasional watering over the years? You might check the ground circuit to the ECU also. The ECU has to have a good ground to fire the injectors. You might have rusty ground points.

Zed, at this point I'm willing to try just about anything. I've got an extra injector two lying around somewhere, I could break/tear off the bosch connection and wire it up to a bulb or something to see if it's pulsing right.

Also, the area by the ECU looked pretty dry. I could see a bit of moisture creeping along the door sills, but it wasn't in contact with the ECU itself.

[FastWoman]

KD, considering your carwash experience, I would now be astonished if your problem isn't electrical. Pull the cover off of your throttle position sensor when that happens to see if you have water between the contacts. If so, just blow it out. That's a common car-wash-related problem. Obviously ignition is the other, as you've alluded. I'd replace every ignition service-related item that has any age on it at all -- cap, rotor, wires, plugs.

I suppose it's possible your ECU got a blast of water, based on what you're writing. However, it has a pretty tight box and sits behind that plastic kick panel (or is yours removed?). Just have a look: Pull the big connector (WITH THE IGNITION OFF). Is there moisture inside? Open up the box. Is there moisture inside there? There's your answer.

Your ECU triggers off of the (-) terminal of the ignition coil, so you might have an issue there. Just another thing to check.

My best guess is that you've got some bad connectors in the engine compartment -- crumbly, leaky, corroded. How would you describe their condition? I'd pay special attention to the sensor connections -- TPS, CTS, AFM. I'd say you got 1/4 mi down the road before current passage started corroding one of your connections, to the extent that electrical contact was lost. All of those Bosch connectors have water seals. I'm guessing yours have lost their integrity. (Am I right?) Replacement 2-conductor connectors are available on Ebay very cheaply. A seller named "forest" (something like that) sells them. Search "280Z injector connectors" to find them. It's the same connector for the injector, cold start valve, thermotime switch, water sensor, and air valve. You can snip the 3-wire TPS connector off of a more modern junkyard car or pay an outrageous price for a used one off of Ebay. Your AFM connector should be in good condition with a bit of cleaning. Use dielectric grease to improve all of your connections and seal out water.

[FastWoman]

Looking at your video, I see some bare wires beneath that loom material, and I see a crumbled rubber boot on your cold start valve. I'm guessing those are your original connectors. If so, the ones on the front of the engine and on your injectors are probably crumbly. I'd replace that stuff. I'd also wrap up your wiring harness with electrical tape, rather than the plastic loom material. That will keep the water out if you wrap it well.

Oh, and just because you have electrical issues doesn't mean you don't have other issues too. In my experience, any car older than 10 years, maintained in a typical manner (or even fairly well) has at least a few engine problems, if not many of them. Even my own engine has one problem -- a faulty air regulator (Grrrrrr.... Just replaced it. Might have to break down an order a NEW one.) So if I were you, I'd go on a general search for other issues, including vacuum leaks. You should contemplate this issue while enjoying a refreshing cup of Yotastic yogurt.

Edited June 22, 2011 by FastWoman

[FastWoman]

PS your vacuum of 14.5 reflects an inefficiency somewhere. It always does -- any engine, anywhere. (Well, maybe not with Model T engines. Dunno.) You should be pulling 17 or 18. So when your engine was running fine before with 14.5" vacuum, it really wasn't. You just didn't realize it. Thus my point, almost all old engines have multiple problems of which their owners are absolutely unaware.

Edited June 22, 2011 by FastWoman

[Zed Head]

The video looks like the engine is running on fewer than 6 cylinders. If it was ignition and your injectors were firing, your plugs should show rich. But if you're sure that you're running lean, then it might be injector related, or it might be a lean misifre.

The test light on an injector plug is a good idea. The engine will run on less than 6 cylinders so you might be able to see an intermittent loss of grounding. FastWoman has mentioned the Christmas tree bulb across the connector pins in previous posts (maybe this topic also). I would get the engine running, pull the injector plugs one at a time, stick the light across the pins and see what you can learn. You might find that it's isolated to just a few cylinders. You might be able to see a variation in the flashing light. At 600 RPM, one injector should flash at 600 RPM. Might be hard to see. That's many mights but intermittent electrical problems are hard to find.

The light test might not show everything though. If your injector plugs are corroded or loose you might not be getting good current through to open the injectors, even though the test light shows current. So make sure that you have good connection to the injectors. The test light or Christmas light might not show a bad connection at the injector.

Last thought - I just saw a post on another forum with a picture of the PCV hose. It was cracked. The PCV hose is difficult to see because it's buried under the manifold but if it has a hole it will create a vacuum leak. The intake/crankcase leak down test will help find that if it's the case. Sorry FastWoman, I went generic on your test name. I haven't had yogurt in quite a while.

Edited June 22, 2011 by Zed Head

[KDMatt]

Hey guys, thanks for the quick responses.

@FastWoman: Indeed, I'd be atonished now too if it weren't electrical ... this just means I seemingly have miles and miles of wiring to climb through now, which has me less than enthused.

I'll take some pics of the ignition components, just for arguments' sake, but I truly believe they're a-ok.

I pulled apart the ECU, there were a few dirty looking solder joints, and I resoldered them. Other than that there was no obvious evidence of moisture in there.

The terminals on the coil have all been cleaned (the coil itself, in fact, has just over 20,000 miles on it) -- it's one of those Accel Super Stock coils. We tried swapping a stock coil back in, and it actually made it run noticeably worse.

The connections on the TPS, AFM, and CTS all seem to be fine (i.e. they look metallic and not green/corroded).

I actually bought a bunch of connectors from that "forrest" guy on ebay, and replaced the Bosch connectors on all six injectors, plus the CTS, so those all ought to be nominal. I'll pull them and look again though if you think that's a good idea. I also had all of my injectors sonic cleaned and refurbished at about the same time.

Also, yeah ... the vacuum isn't ideal. My only point was that I don't believe the low vacuum to be the direct cause of my current problem (again, I'm open to being wrong about this) -- I was only pointing out that the car was running pretty well before (running rich, in fact), with the vacuum about where it is now.

@ZedHead: Yeah, I remember at one point when this first started setting on, I could pull the injector clip off of #4 or #5 pretty interchangeably and not see much of a difference in the running condition of the engine.

Are you talking about those tiny christmas tree lights? I have lots of those.

I'll check out the PCV hose as well.

Anything else I missed?

Oh, and here's an idea I had. To make this is easy as possible for you helpful folks, I'm going to try and take pics of everything.... granted I'll be using my phone, so the pics may not be brilliant, but they'll be something nonetheless.

Here's an overhead pic of my engine, and I'll go investigate anything anybody thinks looks a bit suspicious, and then take pics of that.

Thanks again for all the help so far.

[Zed Head]

Brake booster and hose.

FastWoman's test will tell you though, whether or not you have a problem. Might save you some time or give you some direction.

[FastWoman]

Zed, "intake/crankcase leakdown test" it is -- best performed with a yogurt cup.

Yeah, KD, that will tell you whether you have any issues with the PCV hose. The test will instantly rule out quite a lot.

And indeed, we're talking about the miniature christmas light bulbs. Just pull one out of its socket, and plug into your injector connector. It's a similar resistance and will flash when you get voltage to the connector.

I'm glad you've got some new connectors on your injectors. Although you apparently didn't do your thermotime switch and cold start injector connectors, those wouldn't really be a problem while the engine is running.

There's a drop resistor assembly beneath your master cylinders that's in series with your injectors. You might check those connectors.

Also, how were all the bullet connectors inside your engine harness when you peeled it apart? And how did you make your new connections? (Some people just twist wires together, so I guess one has to ask.)

Tell me about the connection between your AFM and throttle body. You've rigged something there besides the stock boot. Is it completely air tight? If you've got unmetered air leaking into there, you're going to have a lean-running issue. You can still buy a stock boot for roughly $50 from a Nissan dealer.

Regarding the vacuum: Your engine won't run badly because of a low vacuum. Rather, you'll have a low vacuum because your engine is running badly. You've reversed the cause and effect.

Ignition: You might try spraying down your engine compartment at night (with a cool engine, please!) and seeing if you can replicate your poor running. Then with the lights off, watch your engine for any stray sparks. You could easily have a tiny break in your insulation or a carbon trace somewhere, resulting in an ignition short.

No more ideas tonight!

[KDMatt]

Brake booster and hose.

Done and done. I replaced the brake booster a couple of years ago, when it was leaking it was pretty obvious (I just never bothered to paint the new one, d'oh!)

Does that help?

@ Fastwoman: Sorry, haven't had a chance to do the yogurt cup test yet (need to track down a place that'll sell me Yotastic, anything else I can use if I can't get any luck?)

I also haven't peeled apart the harness just yet (it's been raining a ton, so I didn't get any time on the car until last night). I did some more circuit testing and cleaned up some more connections. Everything still seems A-OK, sans how it's actually running.

In terms of the new connectors, I did the coolant temp sensor, and the six injectors. I skipped the thermotime switch and cold start because, like you said, they don't do much when running. I usually have my cold start disconnected anyway because it leaks! I only have it connected now as a last-ditch effort, hoping it'll richen up my mixture a bit as a result.

My new connections were made by soldering the copper wire together (after a twist), then wrapping with electrical tape.

I'll check out the dropping resistors, but I've physically cleaned their grounds, and also tested them according to the FSM, and, if memory serves, they came back fine.

I had a leak once at my custom intake near the throttle, but this was pretty obvious when it happened as I could both hear and feel the air leaking through. Then, when I'd wrap my hand around the intake, my covering the leak would cause the engine to run a bit better. However, I'll check it out again. Like I said, at this point I'm willing to explore any avenue of possibility, as my brain alone has not yielded much success.

Interesting factoid about vacuum.

I'll give the engine a bit of spray tonight and see what happens (oh, and I'll see if I can grab some pics of my ignition components before I do, just for you.)

Anything else I'm forgetting or I can do for anyone? :/

[FastWoman]

Twist, solder, and tape is good, but only if the tape is then taped up (and stabilized) inside tape wrapping around the entire bundle of wires. (Heat shrink tubing is better, BTW.) Nissan constructed some of the harness this way -- well, with crimping instead of soldering. Check to see if your insulation came loose somewhere on your CTS wiring. If you have a short, that could create an extreme lean condition.

The best way to troubleshoot all of your wiring, BTW, is to do the electrical tests described in the FSM at the level of the ECU's large connector. If you have a short or open circuit somewhere, you'll be able to locate/measure it there.

Yogurt cup test: Dunno.... Search around your kitchen for a cup, bottle, jar, or whatever will stuff inside the mouth of the boot and seal it. I only joke about the Yotastic yogurt cup, but it's not something essential. Just find something that will stuff up the hole.

Keep looking! There's a gremlin or three hiding in there SOMEWHERE!

Edited June 24, 2011 by FastWoman