So, my buddy and I took on a job of fixing a co-worker's car. He's got a 1990 Maxima. He drove the car until it got really hot and then he drove it some more. He drove it until it just quit running altogether. Come to find out, he hasn't had heat in his car since winter of 2000.

So, his heater core popped, sent coolant all over his interior. Don't know how familiar you with the placement of the ECU, but it's located directly beneath the Heater Core. Yep, dumped coolant all over the ECU.

So, we pulled the intake, and heads, took them down to the head shop to have them checked over, planed and cleaned, then put a new gasket set on it and put new timing belt and water pump and then pulled the dash (the entire freaking dash!!!) to replace the heater core. We got that put in.

The car will start and run, but it doesn't run very long and it flashes the check engine light. Also, the engine computer control relay buzzes when the key is turned to the off position. So, we went and found another computer out of 90 Maxima in a junkyard and also pulled it's relay too.

Here's the kicker. The car will start and run (but poorly) with either computer in there. The relay also buzzes with either relay in there as well.

So, then we cross reference the part number of the ECU that came from the junkyard and discovered that that ECU is from a 1992!! So how did it end up in a 1990 Maxima in the junkyard?!?

I checked to see and found that only 89, 90, and 91 Maxima ECU's will interchange.

We need some serious help as we've had the car for 3 weeks waiting on various parts and we need the garage space for other projects.

Chris

 

Um, whats the question?

 

so you're saying you need an ecu for an 89-91 Max??


www.car-part.com

 

And smack your co-worker upside the head for driving a hot car....

 

with all those cars you dont have a max?? you should be flogged!!!

 

After seeing the condition his co-worker's was in, do you blame him for not owning one?!

 

Well, in my confusing post I embedded several questions. One, why does the relay buzz? Two, why does the car run like crap? Three, what is the real problem here?

Well, my buddy and I put our heads together last night and came up with this. Why does a relay buzz? Anyone? Well, this particular relay has two live powers a ground and a signal. It is being a fed a loose ground somehow and causing it to quickly open and close. So, somewhere, a power is shorting to ground, causing the baking of an ECU and a buzzing relay.

We opened up the main harness and found at least 9 or 10 wires spliced in with electrical tape. I'm assuming this isn't factory. Well, when we grab one of them and tug at it's splice, the relay quits buzzing.

Now we just have to figure out why all those wires were spliced in there.

The redneck who previously worked on this car used silicon instead of gaskets and made several hacks to make it run right. Now we have to undo what he did and make everything correct. Wheeee!!!

Now, to answer some of the questions presented above. You ask why I don't own a Maxima? Never had an intense desire to own one. I owned a 5 speed FWD Stealth and decided at that point I really have no desire to own another high powered front-wheel drive car. Plus, you see them everywhere. Most of them are ragged out and dirty, at least around here.

I collect and build Audi's because no one else will. You hardly ever see them on the road anymore, because shops charge too much to work on them and people don't have the patience to deal with the cars' quirks. And when people get tired of them, they get rid of them for around $200 to $300 per car. I fix them, sell them and turn a pretty good profit and get the satisfaction of knowing I've built up a pretty reliable car. I've owned 7 of them and built them for friends and co-workers. The turbo cars are fast and sure-footed in foul weather and that's appealing to me.

After this experience, I might get into Maxima's if I can pick them up cheap enough.

Chris

 

It sounds to me like the repairs on this vehicle will be greater than the car's value. I am assuming you are doing all this work for free?

If not, then I would definetly try 2 things:

1. Replace the ECU with an ECU from a 90 that hasnt been hacked into.

2. Check over the ignition wiring for shorts.

Man you are either crazy, or a dang good friend to have around to take on a project like this!

 

Well, we're not doing it for free, but we're doing it for about $2000. Which I think is pretty reasonable for parts and labor. We will be going through the wiring this afternoon.

Chris

 

Way to help, guys...

I send a buddy of mine over from another bulliton board giving you guys high recommendations... and the majority of you come back with completely useless replies.

Thanks for the couple of you that did try to help, though. Just as an update- he found the problem (ground short) and got it fixed.

 

No offense dude, but his problems had so many broad possibilities that there is no way in hell that I or anyone else could have diagnosed it. Suggestions? Sure I could have suggested a few hundred things, but what's the point of that? You should know that electrical problems, especially ones this involved, are very difficult to diagnose wihtout actually seeing what's going on. I could have told him to grab a test light and look for a short, but you probably would have considered that useless too, as it is an obvious course of action to take.

cbpldc, I think I speak for everyone when I say don't ever hesitate to post questions here, I and many others really like helping people out. Just know that sometimes the problems are so deep that the only way to really help is to be there and have a visual. Good luck with the repairs.

 

male,
Thanks for the support. I guess I just needed a night to sleep on it to figure out what the problem was. The buzzing relay was what bothered me the most. We will be taking down the car to the timing belt later and resetting it. We think we may be a tooth off, which would cause the wierd little problems.

Threxx, as always, thank you sir.

Chris

 

Any time chris. So you did the heater core huh? I have no heat around town, I believe the core is blocked up. Was it really necessary to take the entire dash out to replace it?

 

Yep. The entire dash assembly. I have pictures of the chaos, if you' like to see. In fact, you have to loosen the metal crash bar that goes across the underside of the dash that the steering column is bolted to. Tip: Carefully replace all of your wiring looms in the positions that they came from. We had to tear it all down again to move one back.

Check your carpets to see if they are a little wet.

Chris

 

I really don't want to do this. I know it is just like anything else, take it step by step and it's no big deal, but considering the heater core is like $300 and I have to tear the dash completely apart to get it out, I was considering just ghetto rigging my heat by mounting two of those 3000 BTUH electric heaters from JC whitney under the dash, one on the passenger side under the glove comp, one on the drivers side under the column. It would work, no warmup time, easy to install and would cost 1/3 the price even if I was to install the core myself. Make sense, especially now that it's cold out and doing work like this in the cold absolutely sucks. Maybe just to hold me over until spring ya know. What do you think? Can the core be installed in one day? BTW, my core isn't leaking, just doesn't get hot, as I suspect it is blocked. The previous owner put that Bars leaks in the cooling system to seal a leak somewhere. That has to be it. When I slide the heater control lever over to hot, I hear a positive thunk, so it seems like the damper is switching to hot properly, plus, I get heat on the highway when the car has been hot for 20 min or so and the rpm are held steady. If I coast in neutral around town and hold rpm at about 3k (I don't make a habit of this, just to see what's upi with the heat) it gets warmer. Damn this heat! I'm going electric!

 

Well, I would bypass the heater core just in case. That is if you're serious about adding those electric heaters. I think it would be more of a headache than it's worth, and by the time it's said and done you could have taken the dash out and put it back in in about 8 hours time. That's just a Saturday, man.

Also, we picked up our heater core from the Nissan dealer for like $150 or less. Call Dave Burt Nissan in Indy.

Good luck.


Chris

 

hmmm..$150? That's more like it. Maybe it's time I buckle own and get that dash apart! Thanks for the suggestions.

 

maybe it's just the cable on the lever on the left side of the air control thingy. i've heard of that being a problem before. that lever is what runs the water through the heater so maybe check that out first.

 

Do you mean the lever that goes up and down (outside air damper) or left to right (temp control)? I think the temp control (horizontal one) opens and closes the valve. The one all the way to the left that shows a stick figure in a seated position opens and closes the outside air inlet. If you have that in the position showing blue lines at his head, you are letting cold outside air in. The end of the cable does fall off the control lever at the duct (down in the footwell), but that's OK on mine. Liek I said, when I switch the temp cotrol back and forth, it gives a nice thunk adn feels like it is workiing OK. The fact that the temp coming out of the vents depends on how fast my engine is spinning leads me to believe there is a restriction. At first I thought I'd clean out the control valve under the hood, but then I figured if something blocked that up, it sure as hell blocked the core's little orifices (hehe..) too. So I'm resigned to the fact that my core is plugged up. As the water pump speeds up, it forces more water through the core making a noticible temp change. Damn that dashboard. Why couldn't it be an easy job dammit.

 

yeah, i was talking about the vertical one. i think i read somewhere that when you switch it down it runs the water to through the heater. when switched up it is not running through it and lets outside air in.

 

Yeah man i hear yeah, My car did the EXACT same thing, ECU and AT control unit SOAKED! I bought it that way and didnt know it. Till i tried to diagnose my tranny. But yeah I had to take ALL of the stupid dash out, as per my sig pic.

But I used to own a 1986 Audi 4000S, man alive I could beat it (not that I would) and it would NEVER let me down, almost had it to 200,000 till some tard in a jetta sideswiped me. First car and best car I ever owned, but that led me to the 1990 Maxima GXE I own now, and never regreted it, great car! Though I miss my Audi


just ramblin

 

Just a random question, but why wouldn't/couldn't it be the thermostat, male??

 

Wouldnt the engine start to overheat if the thermostat was bad? I dunno about that, but yeah on mine it turned out to be the core.