# 87 Hardbody AIV replacement--it was shot!



## wilburk (Dec 29, 2012)

Just replaced the AIV on my dad's 1987 pickup. It's been missing and backfiring during sudden acceleration and this was one of the things we checked. The underside was completely rusted through, and the filter fell apart like sand at the touch of a finger. 



















But it didn't solve the problem. Truck idles FINE, and even runs ok with SLOW acceleration. Giving it gas suddenly--clutch in or out, doesn't matter--causes it to miss, backfire, shudder, and sometimes even die. Engine temperature doesn't seem to matter. 

So far we've checked spark plugs, distributor, air filter, and timing. Timing has NOT changed since the problem started and we've doubled checked to make sure it hasn't changed.

Have the FSM, and will check out air flow meter, exhaust gas sensor next.

Anyone else experienced this problem? Any thoughts/suggestions?


----------



## yellowrosefarm (Dec 11, 2011)

Yes, I'm having the same problem now with my 88 and at least 3 other people on here are also experiencing it. If you slowly press the throttle it will rev, but if you get on it hard, it cuts in and out. Today, I pulled the air filter cover, worked the throttle by hand to get it to act stupid and sprayed 2+2 gum cutter (carb cleaner) down the throat. It made no difference at all so I'm saying it isn't fuel related. I have a spare good distributor which I'll swap in soon and see if that makes a difference. I'm sure if one of the 4 of us finds a solution, it will fix the others also.


----------



## wilburk (Dec 29, 2012)

Thanks for chiming in yellowrosefarm. I read a few others posts that seemed similar, too.

Good idea with the carb cleaner. That doesn't totally rule out the fuel system does it? Is the carb the _only_ part that controls the air mixture ratio? Guess I don't know enough about that.

Really does sound like it's missing and stumbling though, so it really surprised me that adjusting the timing wasn't making any difference. 

Was wondering about the exhaust system, too...

Keep me posted! :thumbup:


----------



## wilburk (Dec 29, 2012)

If you're one of the people who also have this problem, speak up! Let's figure this out...


----------



## smj999smj (Jan 1, 2006)

In the aluminum housing on the AIV (the part that has the hose going to it) is a reed valve assy. Make sure the reeds are flat and not warped. If they are not laying down flat, replaced the reed valve assy.


----------



## wilburk (Dec 29, 2012)

smj999smj said:


> In the aluminum housing on the AIV (the part that has the hose going to it) is a reed valve assy. Make sure the reeds are flat and not warped. If they are not laying down flat, replaced the reed valve assy.


Saw that diagram in the Haynes manual. Assumed the reed valve on the new AIV would be fine--maybe wrongly. I'll check it today. Thanks for the idea.


----------



## wilburk (Dec 29, 2012)

Both reed valvues looked fine when I checked today. 

Ran ECU diagnostic but LEDs kept blinking together (red and green) 1, 2, 3, 4, 5 times, then reset. My first time doing this, but I was following FSM steps. Any pointers?


----------



## smj999smj (Jan 1, 2006)

You have a 5 mode system, so you have to switch into the mode you want. Mode 3 is the self-diagnostic mode which would have the stored trouble codes. Try this link:

http://www.troublecodes.net/Nissan/pre88nssn.shtml


----------



## wilburk (Dec 29, 2012)

Thanks smj.

After reading more carefully and looking at the diagram of the ecu more carefully, I realized that the diagnostic mode selector switch is the part that I was overlooking. And it's not accessible because the ecu is jammed so far forward. It's close to the led indicators, but still covered by part of the trim/floor. 

Looks like I'm going to have to take off the seat.

Thanks for being understanding with someone who's learning!

Will post update when I read the code...:fluffy:


----------



## wilburk (Dec 29, 2012)

Another thing that confused me initially is that there is the diagnostic mode ON/OFF switch _on the back under the plastic cover_ and then the selector in the front (that I can't see).


----------



## yellowrosefarm (Dec 11, 2011)

My 88 ECU also is blinking both lights together. 1 slow flash, 2 slow flashes, 3 fast flashes, 4 fast flashes, 5 fast flashes, repeat. There is no mode selector on this ECU, only the on/off switch. I tried using the on/off switch as the mode selector and have disconnected the battery but the lights always flash the same.


----------



## wilburk (Dec 29, 2012)

yellowrosefarm said:


> My 88 ECU also is blinking both lights together. 1 slow flash, 2 slow flashes, 3 fast flashes, 4 fast flashes, 5 fast flashes, repeat. There is no mode selector on this ECU, only the on/off switch. I tried using the on/off switch as the mode selector and have disconnected the battery but the lights always flash the same.


Hmmm, are you sure that the mode selector isn't just covered and/or you can't see it?

Here's a super ghetto photoshopped version of my view:










I can see the LED window pretty clearly, but then the floor bumps up towards the transmission and that covers the mode selector. Is that maybe the case with yours?

I'm going to take the seats out (bench seat) soon and take a closer look...

Thanks for posting updates.


----------



## yellowrosefarm (Dec 11, 2011)

I have the seat out so it's no problem to see everything. I even pulled the top off the ECU and looked inside. There are no other holes in the case besides the on/off switch.


----------



## wilburk (Dec 29, 2012)

yellowrosefarm said:


> I have the seat out so it's no problem to see everything. I even pulled the top off the ECU and looked inside. There are no other holes in the case besides the on/off switch.


Weird. So the only things on your ecu are on/off switch, LEDs, and place where cords plug in? I wonder if anyone else has experienced this...

And I hope the same thing doesn't happen when I take out my seat!


----------



## yellowrosefarm (Dec 11, 2011)

Yes, my 86.5 is the same. Only the on/off switch, no mode selector. I did some testing on mine this evening per the factory service manual and it appears the power transistor for the intake coil is bad on my 88. It's only supposed to pass current one way between terminals 1&4 and 1&2 and this one passes both directions. So, I'll have to get a known good used one or a new one and go from there.
BTW, for anyone reading this thread who is wondering which coil is which. The one with a 4 pin connector from the power transistor to the truck wire harness is the intake. The 3 pin connector is the exhaust. Both of my trucks have the exhaust coil toward the front of the truck with a 90 degree boot on the coil wire. On the distributor cap, the exhaust tower is the lower down of the two and both of my caps are labeled E or I.


----------



## wilburk (Dec 29, 2012)

Haha I have to be honest and say that most of what you wrote went beyond my knowledge of late 80's nissan truck ecus. 

So what you're saying is you're replacing your intake coil? How exactly does that effect your ecu diagnostic readouts?

:waving:


----------



## yellowrosefarm (Dec 11, 2011)

Don't know if it would have anything to do with the ECU but it sure could keep the engine from running right.


----------



## wilburk (Dec 29, 2012)

Ohhh so you were just saying the result that the code gave you...

I'm still in the figuring out the code stages. How did you get the code if you didn't have the mode selector?


----------



## yellowrosefarm (Dec 11, 2011)

I don't have a code, just working through some ole time meckanic diagosticating.


----------



## wilburk (Dec 29, 2012)

Oh right on. I've been doing that on and off recently.

Next step may be to go pay a mechanic to diagnose, but NOT fix.


----------



## yellowrosefarm (Dec 11, 2011)

OK, I figured out what was going on with the ECU. The 5 flashes are indeed the 5 modes. The switch is in the "on" position to view the lights flashing together. When the mode you want flashes, in my case #3, you turn the switch off. Then wait............a pretty long time and the codes will start to flash. In my case I got 2 flashes on the red and 1 on the green for 21, ignition signal. That, of course, agrees with my finding of the intake module being bad. My 86.6 only has the diagnostic mode. Turn the switch on and you get the codes.


----------



## wilburk (Dec 29, 2012)

Oh nice, I'll definitely try turning it off when it gets to the right mode. I was kind of playing around with turning it on and off but nothing came about. Maybe this will work.

Also, could you explain what you mean by 86.6, etc.?

thankssssssss


----------



## smj999smj (Jan 1, 2006)

He means "86.5." The last year for the 720 pickup was 1986; later that year, the Hardbody was released as an 86-1/2 model.


----------



## wilburk (Dec 29, 2012)

Awesome--thanks for the update on the lingo.


----------



## wilburk (Dec 29, 2012)

Fixed the truck!

Finally figured out how to check the ecm on the third diagnostic mode thanks to various users. Gave me a '44' code--all OK. Hmmmmm.

Then remembered advice from some to check the ignition coil. Turns out, the cable from the ignition coil to the distributor was...get this...LOOSE. That's all. The little rubber housing over the connection kept slipping off and the connection wasn't that tight in the first place. Did some testing of this hypothesis and it turned out to totally fix the problem. Pushed it in tight, threw a hose clamp on, and have been gunning it no problem. No cutting out, backfiring, etc.

Huge thanks to yellowrosefarm, smj, and all others who chimed in and whos random posts I read after searching.


----------



## yellowrosefarm (Dec 11, 2011)

Hey, that's great news! Congratulations.


----------



## yellowrosefarm (Dec 11, 2011)

The intake coil module came today and it fixed the problem. Now that the intake side is firing like it's supposed to I can rev it up without the cutting in and out. I think the coil was probably OK and it was the module all along. Cost about 50 bucks for the module from rock auto.


----------



## wilburk (Dec 29, 2012)

Ok so my hose clamp seems to have been a temporary fix...another sputter, power loss, skip, and dead car! 

yellowrosefarm, did your 88 only have one coil? Are there potentially two? Thinking that replacing the coil is the next logical step (since the connection seemed to fix it temporarily). It's cracked through and rusting.


----------



## yellowrosefarm (Dec 11, 2011)

Yes, all z24's have 2 coils. One to fire the 4 exhaust spark plugs and 1 to fire the 4 intake ones. The computer (ecm) turns off the exhaust coil above about 2500 rpm, which, I assume, is why my engine was cutting in and out. I had replaced the exhaust coil already when it wouldn't start at all, not knowing then which coil was which. I think the intake coil itself was probably OK but the module was bad. Oh well, having two new coils is a good thing and they aren't too expensive. ($36 at NAPA). Your problem may still be a bad connection rather than a bad component. If it will start and run then push/pull/wiggle/jiggle all the coil/distributor connections and see if it cuts off.


----------



## wilburk (Dec 29, 2012)

Found the other ignition coil...it was RIGHT next to the other one. Haha.

Spent some time idling the truck today and wiggling distributor leads. Nothing really happened unless I pulled them all the way off. Think it probably isn't the coil.

It's still getting bogged down when accelerating. And then dying. Sounds like it's getting smothered. Wondering if it's a fuel issue...

It's seeming like it's worse when it's warmed up. Like 5-10 minutes or so. This seems like some sort of clue.

Today I re-checked:
1. EGR valve
2. distributor cap, leads, contact points
3. fuel filter (didn't replace, but the fuel that came spilling out was crystal clear)
4. Visual inspection of carb and it looked really clean (I know this doesn't necessarily mean a ton)

Any other ideas? You've been super helpful so far!


----------



## yellowrosefarm (Dec 11, 2011)

This is a long shot but I'm wondering if the catalyitic convertor is stopped up. Your saying it sounds like it is being smothered out is what brought that to mind. Do you know anyone with an infared temperature gun you could borrow?
With that, you could check the temp of the unit at the inlet and outlet to see how big a difference there is. Without it, you could run it as hard as you could, then look underneath and see if the cat is glowing red. I had an Isuzu and a Dodge that the cat stopped up on. The isuzu cat did glow cherry red after pulling a hill. The Dodge just lost all power and wouldn't pull a hill.


----------



## wilburk (Dec 29, 2012)

Interesting idea--I'll check it out tomorrow. Don't know anyone with a temp gun, but I'll run it hard and see what I can see. 

Took out both coils today and tested resistance. They're a bit below the haynes manual specs, but the resistance is identical. This makes me think they're ok...


----------



## wilburk (Dec 29, 2012)

Ok so finally got around the replacing the primary coil today. It has fixed the bogging/dying problems when given gas. I think this mystery has finally been solved! :fluffy:

You can see the cracks in the side of the coils--likely water had gotten in and rusted/destroyed the coils. The spark was probably jumping out of the side of the darn thing!










Even the mounting brackets (or whatever) were super rusted out.










So it's fixed. Thanks to all who helped along the way.


----------

