3500 rpm stumble 240zx 280zx Maxima L motor - FIXED!

[HRH]

Okay, so on Ugly Betty, she runs fine, but since I've had her, she's had a little stumble at 3500 rpm, usually if I hold it there.  RPMs don't drop, but you can definitely feel it cut out like it's missing.  Not bad, you can drive through it.  Idles high since I haven't adjusted the air bypass valve since I gutted the airbox and deleted the cat.  Put your foot down, she responds nicely.

 

In chasing it, I found the vacuum advance can on the distributor to be bad.  Plugged that.  The 82-84 Maximas had matchbox 6 cylinder distributors with a secondary connection that is an idle control, interestingly enough.  Think regular looking matchbox but with a two-prong injector connector on the side.  If you disconnect the idle control, it still runs just fine, but the spark curve seems to be rather weak.  Probably exacerbated by the fact that the vacuum advance is not in operation at current.

 

Have not replaced ALL the vacuum lines yet, but don't think I have any other leaks.  Intake/exhaust gasket was done, it's good, retorqued, no leaks.  Replaced both AFM and TPS.  I'm debating the correct position for TPS.  Going to check the manual, but as far as I know, it should have continuity at idle and right off idle go into the mid circuit, so that's how I have it hooked up.  Read some blurb online that it should remain on idle circuit until 1/3 throttle, which I think is incorrect, hence my double checking.

 

Anyway, I know the distributor is a little screwed up.  The vacuum advance is plugged (not a problem) and the advance plate is broken with a ball jammed in the side, which could be affecting the centrifugal weights (possible problem).  I have a new one on order and may do some junkyard diving today.  The hesitation is much more noticeable when she's bone cold in the morning, until it's hot out.  When she's warm and the ambient temperature is warm, the hesitation is nearly gone, but it's still there.  I was thinking the matchbox as it is an original unit, but seems as though it would fail on hot, not on cold.  Have not tested it yet, but will.

 

Since the tach isn't dropping out, I am assuming it's not electrical-related, which leads me back to fuel pump with that funky diaphragm valve.  From what I've seen though, when those fail, they cease to run or have a hard time starting.  It shouldn't have a pressure issue at 3500 rpm and then fine at idle and fine at WOT.

 

I'm also going to take off the air boot today and clean out the throttle body, just to see if I have some crap in there.

 

Aside from that, anyone have any ideas? 

 

Just confirmed the matchbox unit for four cylinders doesn't care if it's 6 or 4.  I thought it mattered, but interchange on the NAPA website shows both Maximas and 710s use the same version, so bingo, think I have an extra unit somewhere in the garage I can throw in for testing.

[q-tip]

I would point my finger at the fucked up dizzy.

[I'm BLUE]

You found your Vacuum Advance is shit.

You found your breaker plate is shit with a ball fallen out jamming the timing advance/breakerplate.

You have that funky 4-prong e12-92 ignition module which "can" be shitty since it retards your timing until you un-plug the bottom plug ( well at least for a 240z or 280zx conversion)

Nope it's not the dizzy HRH look elsewhere  lol

Just one of these problems would give you some headache I would imagine sounds like you got it licked.

 

I've ordered some parts from Nissancc.com to rebuild my 79' 280zx EI distributor (it's a touch different with an e12-80 module , top bushing style , plate , and does not posess the e12-92).

Can get a breaker plate assembly.

A new vacuum diaphram.

The pickup assembly is relatively cheap as well.

Reluctors are cheap , and so are the roll-pins that go with.

Stators are a decent price even.

You can use a chevy HEI module too if you get sick of the rest or want to do it on the cheap.

 

Make sure to get those really small cruise control vacuum hoses etc to.Those are usually all thrashed.

I've had a 280zx fuel pump ... always work ... always pump ... but would bleed back pressure under load , and cause somewhat consistent miss.

If you haven't already ... pull out and clean your injectors - replace o-rings - clean the connections , replace the injector harnessconnectors , or dump seafoam in the tank if not time.

Not sure if you still have a catalytic converter on the car or even need it in your area ?

Ignition plug wires and coil wires can start leaking outside of their insulation ... at their own will ... as well. I've had coil wires do that a few times (cheap).

The L6 intake/exhaust manifolds front or rear studs will break/spin out or loosen. Just happens. They leak here or there.

The AFM boot between the AFM and the throttle body leak... peel it back with it off and use shoe glue if it's bad for a temp fix ....

CHTS ... not sure it exists in the maxima head , but it does on the 81-83 280zx. Those connectors need to be replaced , and sometimes the sensor.

 

Here's a few pictures of my 79' 280zx distributor being getting taken apart if it's something you want to do with yours for whatever reason (or not) just use a small hammer/fast light taps to get the bushings out... works MUCH better than a big weighted hammer with bigger blows or straight pressure for me at least. I was going to stick it in my press , but didn't want to ruin the distributor body = http://nwdatsuns.com/viewtopic.php?f=16&t=10&start=180

 

 

That's how I really feel HRH ;)

[HRH]

Lol, thanks Blue!  Wait a minute, DTP?  I'm so confused.  Anyway, the pump makes me wonder.  I did get a new pump just for giggles.  I'm tempted to replace it.  There are two pressure dingi on the pump.  On on it, one shortly after it.  I can't remember, why was the second one there?  Was it to prevent fuel hammering, or something, shit, I used to know, it's on the tip of my tongue.  

 

Luckily I have a hoarder gene and I found a matchbox dizzy I yanked at pull and save many moons back.  Tested the vacuum advance, it works great!  So, I'm going to remove the top 4 cylinder reluctor ring and put in the 6 cylinder, or some combination thereof, and that should solve the rest of the distributor problem.  Right now I just got the cover back on the diff, she's been leaking for a while, all sealed up with Right Stuff now.  No more leaks!  Need to go fill it though.  After that I'll drain and refill the trans.  Then I'm starting on the topside work.

 

Yes, injectors are all brand new, intake/exhaust has been resealed, and it has one 10 mm stud in the rear of the head now, that was in the build thread, what a bitch.

 

Your description of the fuel pump issue makes me wonder.  I know those pumps are common for that issue, and it would make sense that when cold it would be more prevalent, when it's hot and everything heats up, it seals a little better and has less issues.  I may just replace the pump anyway since it is a factory 150k pump.  That's asking for it to go out, especially now that it's getting a lot more use with autocross, not just putting around.

 

That's interesting, I just looked at the pump I got, it doesn't have that pressure diaphragm in it.  I'm actually thinking I can get rid of both pressure diaphragms, as I ran the same type of external pump with the EFI in the 510 and never had an issue with fuel pressure. Going to go dig around on the Internet and see if I can find more information as to the function of those and whether or not they're necessary.

[HRH]

Well check this out:

 

http://forums.hybridz.org/topic/70163-fuel-damper/

 

I think I may just remove that section of line and put in the new pump minus dampers and see what happens.  Like I said with the 510 and the bastardized 200sx injection system, which was 4 years earlier technology, I had 0 problems other than a huge cam trying to work with that system.  But no driveability issues at mid or full throttle.

 

Anyone else removed theirs and had bad or good effects?

[datzenmike]

'79 matchbox...  simple

 

 

'84 Maxima matchbox... not so simple.

 

 

You can't use the Maxima matchbox on a regular non EFI matchbox dizzy. As the motor revs up the ignition retards up to 20 degrees. Someone on the Realm had this problem. I think it's some kind of ECU retard for detonation control used on later EFI motors that have this.

[HRH]

Interesting!  Good find Mike!  Good thing I'll be back-dating it.  I'm thinking the problem may lie in my fuel pump/fuel damper though, with Blue's description.  Not to mention the way I've felt the problem, even if the distributor is shitty, it's still working just fine, the only problem is a less than ideal spark curve.  That will make for lack-luster running, but the miss at a specific rpm that doesn't register on the tach seems to me would be more fuel related.  Not sure yet, just got a crapload of 3/8s EFI line.  Looks like a 5 foot run from the sending unit down to the fuel pump.  Need to investigate further, you'd think they'd put a metal line in between but maybe not.  I may skip the line and just do the pump for testing purposes though.

 

And you know, I wondered why they had an ignition control when the distributor was still equipped with vacuum advance.  That explains it, they used the vacuum advance in conjunction with the retard feature so it would have decent pickup from idle to full throttle, but not the full effect.  I ran it to 3000 rpm and it won't go above 33 degrees or so total advance, even when static timing indicates 14 degrees btdc.  Anyway, off to go play some more!

[I'm BLUE]

lol. Yeah I got a new name HRH it's no longer DTP it's "I'm Blue" :D.

Seems like that's well worth a shot using the fuel pump or the old/good fuel pump from your zx.

I think the fuel dampener would have some effect , but I've always wondered if they became more of a nusissance than it's worth like what you maybe experiencing !

Since you're going to be doing auto-cross (I don't know the rules) I'm planning on doing a surge tank or cutting/re-welding a 280zx tank to go into my 240z (we'll see)

Granted like mikes explaining if the circuit board if fawked on your maxima dizzy module ... well ... that's just one more sign there's nothing wrong with your dizzy... :rofl: ;)

You can wire up a spare pump straight to the rail (can.. carefully of course or something sealed) , and take it for a test drive... that should tell you soon enough without getting grief with all the under car work :) .... just zoom by your methhead neighbors and do everyone a favor if ugly betty blows up = they blow up ... WIN WIN !!!

The fuel feed lines back at the tank-to-the-pump have been pretty rotten on some of the zx's I've worked on... expensive ... even the breather lines were questionable at best on 2 of them ...The one feeding the zx fuel pump (big fat angle nippe piece looking thingy) was a total bisch to get ahold of of new for something close to the right size locally. If NAPA didn't have or able to order it I was fawked ;)

 

Thanks for the pics Mike ! I've should have said some of those 240z's have 280zx EFI systems running in them , and some are carbed .. opps lol !

I've never cut one of those later e12-92/93's open (I only own a couple 92's and 80's as well as the Chevy shit lol)... that's a lot of stuff going on there !

Here's a site (classiczcars) that I found the information from a bit ago (he's a member here I believe) , and it makes enough sense = http://www.classiczcars.com/forums/electrical-s30/32137-e12-80-s.html

 

 

 

 

"Okay, so substituting an E12-92 or E1-93 module pulls off timing, but the prongs on the side get signal from the computer to advance timing? Right? Did I read that correctly?" I thought to myself.

Easy enough to theorize what happened next. All I had to do was run a wire with 12 volts (spliced from positive post on coil) to one of the pins on the side of the E12-93 module, and gained back 5º of timing (iirc). It's wired to the I pin, but the W pin does the same thing.

After that, I simply adjusted the distributor to give me 18º btdc @ idle, and it has run flawlessly for over 1,500 miles. Pulls cleanly to 8K RPM too (although I do have the head and cam to make it there).

Well, there you have it. Now anyone can run the E12-92 or E12-93 modules which have been completely worthless up until now.

 

- blue 72

 

Last edited by blue 72; 10-05-2008 at 05:34 PM.

'72 240Z - F54, P79, '78 5 Speed, 3.9 R200

 

[HRH]

So I'm almost ready to go at the fuel pump, and as I was getting ready to refill the transmission (oil looked great) I realized when I Right-Stuffed the diff cover, I ran a bead around the edge of the diff and went to the outside of the bolt holes except on the bottom bolts, where I went around both sides.  I sealed the thing up and then began thinking, hmm, that's going to allow oil into the threads, which will allow it to travel down the bolt, which may leak.  Not going to yank it off and reseal it, but what do you think, will it leak a little, or leak a lot?  I'm thinking a small amount of seepage from my boner mistake.  Shouldn't be enough to need resealing I'm thinking.  It's not under pressure of course, but still makes me wonder.  Grr. Should have paid more attention.

[datzenmike]

Now that's interesting. Guy on the realm had that module on an L20B matchbox. When revved the timing retarded. Thoughts were : was the vacuum advance on backwards? was there pressure instead of vacuum to the advance, was the motor running backwards, counter weights on backwards, drive gear for dizzy on backwards, dizzy running backwards? on and on. Eventually someone noticed the different module and the extra plug on the side.

[datzenmike]

Sealer should be ok. It would have to get out from under the bolt head and the cover. It's tightened on good. Pretty unlikely.

[HRH]

So I posted last night right when the power flickered during the thunderstorm, and it kicked me off the internet for a bit.  Suffice to say, my post didn't take.  The jist of it was:

I replaced the fuel pump with an aftermarket unit.  Very little debris in the original screen in the original pump, that was a plus.  The rest of the car rusted, not the tank! ;)
Got rid of both fuel dampers.  No problems.  In fact, my very annoying on/off throttle, which would lurch the car in a drive through, is pretty much normal now.  No more backfires after letting off at 6500 rpm on full throttle acceleration runs.

However, the stumble is still there.  Tomorrow my new distributor arrives.  I couldn't wait.  I cannibalized the 4 cylinder extra distributor I had and put the 6 cylinder ring and star wheel in it.  There were some small cracks in the insulator plate near the screw holes, but the ring was intact.  I did crush a corner off the plastic piece that sits in the middle of that.  Doesn't seem to matter so far, we'll see tomorrow morning when I attempt to drive to work.  Really all I'm trying to do is find out if the stumble at 3500 is gone.  If it is, oh joy.  Then I'll hook up the vacuum advance again.  The donor distributor vacuum advance works but the vacuum tube is facing the wrong direction, so it's still disconnected at the moment.

And if it doesn't work, I have a new distributor tomorrow.  I'll probably put that in anyway, just so I don't have to worry about it.  I shall report if the stumble/miss is gone!

Oh, and I got the stereo installed yesterday.  What a bitch, no DIN plates, ended up welding some of the original to the CD player sliding box.  Worked great, but annoying install.  And then during the install, I welded a foot long crack on the inner door skin.  WTF Batman?!  Welded up the top where it cracked too.  Freakin' weird.

[HRH]

AH HAH!!  So after driving down from our quota dinner with the team tonight, I finally had the Maxima leave me stranded.  Fortunately, karma rewarded my gesture of giving the guy at the freeway off-ramp my leftovers. (Longhorn ribs and mashed potatos) Anyway, shortly after that the car died and the tach just continued downward.  So I pulled into a wonderfully bad area to be in at night and started diagnosing.  Figure coil right, the tach went dead, it's attached directly to the coil for signal and power.  The tach lost signal, everything else was still connected, no issues.  I yanked off the coil wire and attempted to start, no arcing out of the coil.  Hmm.  After about 5 seconds, then there was some arcing.  Tried to start it again, tried to catch just not quite.

 

At this point I went into Frank's Diner to pee and call one of my buddies.  About 10 minutes later after I finally got ahold of someone semi-closeby, I tried to start it and viola!, fired up!  So I called him back and told him I was going to try and limp it across the Maple street bridge towards home.  I made it across the bridge, not by that much and she died again.  Tried turning on the 4 way flashers, they wouldn't work.  Interesting.  Had just enough momentum to turn into a side road and I mean like 2 mph of roll.  Guy behind me looked all cranky.  Whatever.  At least he didn't hit me.

 

So I yank off the coil wire again and hit the key.  Arcing normally.  Hmm.  Put it back on, fire it up again.  Go back on Maple, makes it to the Safeway before it dies again.  I push it through the intersection into Safeway's parking lot.  (Good thing I got rid of the 40 pounds of AC system huh?!)  Wait a minute after cooling down from the 100 yard push.  Same thing, check for spark, no spark, then all of a sudden spark.  Fires up.  One last limp down the hill turn left onto my street and I JUST make it to my gate and she dies again.

 

THIS time however, I hear the fuel pump whir for it's 10 second cycle at startup, then it cuts out, then it starts up again.  Turn the key off, fire it back up and park it in the driveway.

 

What I'm thinking is not the coil.  I'm guessing either the ignition switch or the ignition relay is cutting out.  Or the wiring in between.  Given the earlier heater blower switch I fixed, I'm wondering if Nissan skimped on the switch quality and the ignition backing is becoming a problem.  The ignition switch has been a bit hard to turn since I got it.  Tomorrow I'll yank it out from the dash and examine the backing.  From there the relay.  Gotta fix it quick, I'm going to Oregon and Canby!

[ggzilla]

soak your fuse box in vinegar

[HRH]

Fusebox isn't external, it's in front of the glove box on the Maximas.  Looks great.  I'm still thinking the ignition switch and/or ignition relay.

[q-tip]

Bad relay maybe

[ggzilla]

Intermittent wiring connection. Unplug & replug each connector.

[HRH]

^ No shit!  :D  I have a new ignition switch and tumbler to install, as well as the relay for the ignition.  I may just wire in a series of toggles like I had in the 510, but we shall see.  Don't know if I'll get around to it tonight, might be Sunday.  Either way, I'm betting I'm going to find a crappy ignition backing that is failing.

[ggzilla]

Get a new ignition backing if your worried about it.

[HRH]

^ No shit!   :D  I have a new ignition switch and tumbler to install, as well as the relay for the ignition.  I may just wire in a series of toggles like I had in the 510, but we shall see.  Don't know if I'll get around to it tonight, might be Sunday.  Either way, I'm betting I'm going to find a crappy ignition backing that is failing.

 

Ggzilla, you're killing me here! ;)  Did I just not say I have a new ignition switch (backing) and tumbler to install, as well as the ignition relay?  Don't feel too bad, my employees can't read either.  :D

[HRH]

Ok, found out the ignition switch/backing was pretty loose.  Not convinced that was entirely the problem.  However, there are some fairly significant cuts in the insulation of the ignition plug, due to it's close proximity to the tilt mechanism for the wheel.  So, after unsuccessfully getting the ignition cylinder out (pin jammed), I whacked the shit out of it and cemented the fact that I'm going to make a plate for toggles and a push button start.

 

Interestingly, the hazard switch seems to be unrelated as I've found, it's just kind of temperamental and doesn't like to switch on sometimes unless you rock it back slightly.  So throw the hazard switch out of the equation.  The fuel pump double on could have been the backing stuck right between on and acc.  Not sure on that yet.  The fuel pump relay is controlled by the ecu, so there is a slight possibility the ecu is having issues.

 

Short of it is, I'm going to wire in the toggles/push button, then go for a drive.  The relay I would love to replace, except there are about 8 relays and not a damn one of them are marked.  So it's a guessing game at this point because the shitty wiring schematic I have doesn't identify circuits accurately enough.  Fuck Chilton's for trying to cover 6 years of different 810/510/Stanzas/Maxima diesels, etc in one book.  It's absolutely worthless other than basic information.

I have the glove box manual for the car, it is worthless also.  And even in the original picture, the big box plate over the relays doesn't have a location diagram sticker on it.  Bah.

 

That brings me back to either the ignition switch (possible) and/or the ignition coil, and/or the relay, and last the ecu.  Off to go make a switch plate!

 

[HRH]

Okay, so it took waaaaay too long (as usual) to solder all the new connections, drill holes, make a plate, etc.  But I have the car all wired up now except a hidden kill switch.  First time I started her up the tach went wonky.  Thought that was odd.  Realized when I undid the metal cover for the relays, there are two ground wires attached to that that are fairly important.  Probably like the grounds at the voltage regulator on the 510.  Anyway, cleaned those up, ended up putting a bolt and nut in that attachment instead of the sheet metal screw, tach works fine now.

 

Interesting development:  Haven't gone driving yet, but I'm thinking the problem may just have been as simple as a coil.  Reason being, I extracted the old one, lo and behold it was FACTORY Nissan.  :)  Nothing like 150,000 miles!  I have pictures, I'll probably post those later after testing.  Crossing my fingers I don't have any more issues.

[LenRobertson]

Matt - I'm seldom shocked by anything anymore, but I'm shocked you don't have a Factory Service Manual for the Maxy. And I very seldom tell other people what to do, but I'm telling you, go to eBay and buy a FSM! :D If you don't do eBay, PM me. I can get you one and you can pay me back. The place the FSM is invaluable is wiring problems. It breaks all the different electrical bits down into their own little system instead of having a big blurry generic wiring diagram like Useless Chiltons.

 

Len

[HRH]

Yeah, I should do that Len.  Going to go get dinner and do a test drive now.  Have all the tools with me this time so I can diagnose if she dies.

[HRH]

FUCK A DUCK!!  Took her for a test drive, everything seemed all hunky dory, drove around for a half hour with the dog, then went and got dinner.  On the way back, only once, I noticed the tach stall out from 6300 rpm to 6500 rpm, through first and second, but no appreciable loss of speed or other issue.  Then, right before home, she did it again.  Tach needle went to zero, car was dead, but this time I held my foot at the same position, and oddly enough, after coasting for 10 seconds, the damn thing turned on again and I couldn't get her to shut off.

 

Once home, I left her running in the back slab and tapped on all the relays in the box with a ratchet.  Not one closed up and killed the car.  And of course, I couldn't test the stupid car this time because she didn't break down enough.  Going to eat dinner, then more testing.  I'm beginning to wonder if it is a wire or the ECU.  I felt the ECU, didn't feel hot, not that that probably matters.

 

Any ideas?  This is starting to annoy me.  I'm about ready to find some carbs.