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Discussion Starter · #1 ·
Guys before I bore you will the details of how I got here (loss of power mid range and up) I would like someone's input into why a brand new ECU would not provide spark and allow the car to start? It just cranks and cranks but I do smell gas so it's getting fuel. When I take the new one out and plug the old one back in the car fires right up??? Anyone run into this before with a replacement? Thanks
 

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Well now you just gonna get asked a bunch of questions of how you got here and why you think you original ECU was bad. lol

Could be it’s just not the right match, although it may have been listed as compatible.


Sent from my iPhone using Tapatalk
 

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Guys before I bore you will the details of how I got here (loss of power mid range and up) I would like someone's input into why a brand new ECU would not provide spark and allow the car to start? It just cranks and cranks but I do smell gas so it's getting fuel. When I take the new one out and plug the old one back in the car fires right up??? Anyone run into this before with a replacement? Thanks
Where did you get this new ECU? does it look like your old one? does the number match? you might have an incorrect one... they are different depending on year (84,85,86,87, 88 and 89) other factors that may have effect is your O2 sensor and whether your ECU is for turbo or NA.

Bon
 

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Discussion Starter · #4 ·
Where did you get this new ECU? does it look like your old one? does the number match? you might have an incorrect one... they are different depending on year (84,85,86,87, 88 and 89) other factors that may have effect is your O2 sensor and whether your ECU is for turbo or NA.

Bon
Thanks for the reply Bon, I got the ECU from RockAuto and it's for a 85, non Calf emissions, standard trans, non turbo. And it cannot be flashed. On paper it's a match, plugs all match, and it looks just like the old one. This should have been a plug and play unit but like I said it's not allowing spark.
 

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That's really strange. but some of the reman ECUs are either different or don't work (so I've heard) you might just want to try and get a used one from ebay or try steve over at 300zxpartsforyou.com
that way you know it came from the factory. still a strange issue...
what's wrong with your original ECU, is it bad?

Bon
 

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Discussion Starter · #6 ·
That's really strange. but some of the reman ECUs are either different or don't work (so I've heard) you might just want to try and get a used one from ebay or try steve over at 300zxpartsforyou.com
that way you know it came from the factory. still a strange issue...
what's wrong with your original ECU, is it bad?

Bon
Yeah I agree this is very strange. I did look around the wreaking yards here where I live trying to find a used one before I bought this one but these cars are getting harder to find and I did not have any luck there. This all started after covering up an exhaust leak when the car started chocking for power mid to upper range. I suspected it was an vacuum leak which I smoked checked and fixed a few. But the problem didn't go away. Codes were telling me fuel temp sensor, throttle valve switch, air regulator, crankcase sensor, and AC sys malfunction. I replaced the air regulator, CAS sensor and fuel sensor/reg and AC checked ok as did the throttle valve switch. I also replaced the fuel filter. I made sure each plug was getting power which they were. I then suspected the exhaust was chocking off the power and had a local muffler shot cut off the catalytic convertor (which was shot anyways) but that didn't change anything either. The shop manual I use kept taking me back to replace the ECCS on every check I did so that's why I ordered this one. But I didn't expect the engine not to start so now I am stuck again. Two things I have not checked yet are the fuel injectors and the EGR valve and sensor but I am not getting codes for either of those and have doubts they are the cause. This has been a really frustrating event.
 

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I replaced my fuel injectors recently. The symptom was the engine was hard to start. It fixed that. While it may benefit you to replace them, it's a lot of work and doesn't seem like your immediate issue. My EGR system has not worked for many years (probably the same goes for a few of us) and yet have not had the symptoms you described. Make sure none of your spark plugs have cracked insulators, and have dielectric grease applied correctly to prevent arcing. It's a real problem. Also make sure the alternator belt is properly tensioned. I can tell you from experience that aftermarket belts are not the right size so just go with OEM on that. A drive belt is not something you think of for engine trouble, but when that belt slips the engine doesn't run right.
 

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Discussion Starter · #10 ·
Thanks for the reply O, dielectric grease I have never used but will look into it. The alternator belt is tight also. Yeah never had starting issues yet with this problem and like I said I did/have not received a code on the injectors each time I checked the codes. I did have the injectors replaced by my local nissan dealer years ago during the recall and never had any problems after that. I will take a look at the plug leads as you say but when I checked for spark I used the distributor side of the wires to do the check and each one had a solid spark. Next I think I will jack with the timing to see if that changes anything (thinking the change in exhaust flow and/or fixing the vacuum leaks may have effected that setting) but I have my doubts with that solving anything either. I do appreciate your input here however and if I ever solve this I will post back here incase you are one of the other owners has this happen to them.
 

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Discussion Starter · #12 ·
UPDATE: Gave up on the new ECU and sent it back and put the old one back in. Car still starts and idles good but the original problem of a power loss right at 2400 rpm still exists. If I hold the accelerator right at 2400 power drops off to 1500 rpm and then pulsates back and forth between the two rpms. I can power through that range and drive the car but at higher speed there is a significant power loss. No vac leaks, catalytic convertor was cut off with no change, fuel press reg and temp probe check out, spark to every plug, throttle position switch checks, air flow meter checks, and the air regulator valve (new) checks. The latest codes are still giving me 31 for AC system and 41 for Fuel temp sensor circuit which both again check good. Anyone out there ever run into this kind of a problem with their Z31?
85 Std trans, non turbo
 

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how's your air filter?
have you taken your MAF off and examined it?
I think you may be having some kind of problem with your TPS.... even though you said it checked good.
What kind of spark plugs are you using?

Bon
 

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Discussion Starter · #16 ·
I took the air filter completely out when this started and got the same results. The MAF tested and passed and I even unplugged it and the engine ran worse and had trouble starting. I have retested the TPS again with the same results. Plugs are E3s.
 

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Plugs are E3s? Are they NKGs?
This is indeed a very strange issue.

Bon
 

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The Z-cars do have a reputation of running best with NGK plugs. I've tried some of the weird plugs from time to time, and decided they were best designed to lighten my wallet.
 

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Do your Z a favor- take those E3's out and put in NGKs. BCPR5ES, or BCPR6ES. you can get them below.... or at least have a reference. These are also available at local parts stores.
Part# 22401-01P16 or 01P17


Are your injectors all working correctly? I mean per FSM. And also have you looked the CHTS (cylinder head temp sensor) It could be failing, even though it really has to do more with starting up process with ECU and the engine temperature, it wouldn't hurt to check this or even replace it.

Also, as BruceA has already said in the post... Steve over at 300zxpartsforyou.com has correct second-hand ECUs. You could try getting one from him for your year car and see if there is any difference. I don't trust these aftermarket ones, like the one you got and sent back.

Bon
 
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