New ECU but engine dies on throttle

[Guest Clarence A Wood]

Hi all,

I recently posted a request for an ECU for a 1982 280ZXTand have since received one from World Auto Parts. I installed it and the engine was very hard to start. It would kick over a few times then die. I finally got it to idle (by repeated starting attempts) but the engine would die on throttle. I have the large shop model for the car and I went through all of the checks (again) and everything checked out. The engine got up to operating temp by idling and became easy to start (Oxy Sensor was hot and ECU was reading it) but still would die on throttle. I could get the engine to rev by pumping the accelerator peddle rapidly; the engine would almost die but catch and start to speed up, then almost die then speed up and then past 2k rpm throttle response was good but engine did not sound or feel all that smooth.

One thing I did to the engine while I was waiting for the ECU to come in, I adjusted the valves, cold. When the engine was idling I noticed that the fifth and sixth cylinder valves were clicking rather loudly (when the engine warmed the clicking was reduced). Do you think that improper valve lash could cause the problem of not accelerating? I have adjusted valves before and I was careful to do a good job and was surprised that 5 and 6 were loose; the others sounded fine. I have installed a new Oxy sensor. I have looked for vacuum leaks but found none; however, when I removed the oil filler cap the engine does not fall off idle which surprised me. I pulled a main vacuum line of the intake manifold and the engine fell off idle. It seems to me that, when the engine was running well, when the oil filler cap was removed the engine would fall off idle.

I am going nuts over this thing! Please some one drop me a line saying "Oh, I know exactly whats wrong....". I know, NOT.

 

Thanks for your help,

Clarence

[badjuju]

the oxy sensor and valve adjustment aren't your problem, the clicking valves are irritating, but you'd have to adjust them pretty aggressively to have the motor running like you have described it.

 

I'd check electrical connections, your air flow meter, etc.

 

spray some starting fluid around the intake manifold, if the idle goes up, you're hitting a vaccuum leak. Likewise, if you spray wd-40 the same way, and the idle goes down, you're hitting a vaccuum leak.

 

try moving the flap on the air flow meter by hand while it's running, see what sort of changes it makes. do some experimenting.

 

Check fuel pressure

check spark plugs

check your timing

 

what color smoke are you getting?

 

black - not so bad

blue - sorta bad

white - bad

 

eidt:

and welcome to the community. I'm impressed, your first post and doesn't obviously break any forum rules. Don't think that's happened in a while.

[Guest Clarence A Wood]

thanks Badjuju,

just did a timing check, even though I checked the timing while the old ECU was being diagnosed, and instead of being 20deg +-3 it was 3deg at idle of about 600 to 675! I corrected the timing. It seemed to improve the ability to accelerate rpm but there was still dead spots but not as bad.

The temp outside here is 58deg and the exhaust is gray/white. I thought gray was good; why do you think that it is bad? Black=rich; Blue=oil; white=?

Thanks,

Clarence

[Guest Clarence A Wood]

Pay no attention to the bad ignition timing! I was using a timing light that had an adjustable degree option and it was set at 20deg so the actual timing was 23deg instead of 3 deg. It's been a long day....

[Spraguepsycho1]

White smoke is usually water. If it only smokes white when starting it in the morning for a little while then goes away it's usually just condensation that built up in the exhaust as it cooled drawing in colder damp air. If it keeps smoking white after everything's warmed up, it's usually a blown head gasket.

[Guest Clarence A Wood]

Thanks Spraguespsycho1,

tomorrow I will open the radiator cap, if I can get it to start, it will idle and I'll watch for bubbles to see if I have a head gasket leak.

What I can't figure out is what senders to test when the Oxy Sensor is still cold(Open Loop); these sensors tell the ECU how to run the engine. I know one is the Cylinder Head Temp Sensor, and it test out ok. The only other conditions are +3.6krpm or heavy loads or too lean/rich mixture. Gosh, what I seem to be saying is that the ECU is not running the engine under the Open Loop! If something was making it think that it should be running under Closed Loop because the engine is hot then.....

I'm getting a headache.

[Guest Clarence A Wood]

I disconnected the CylBlkTmpSensor and it started and idled just fine. I have been trying to find a thread that I read by someone here who had the same problem but I can't find the thread. As soon as I reconnect the sensor the engine bogs and dies under throttle. I tried to drive the car w/out sensor but it would lose rpm and almost die and then run normal for awhile and then lose rpm. If I put the trans in N the engine would return to normal and would operate under Drive for awhile and then suddenly drop rpm. As long as I went from Drive to Neutral I could limp down the road. The Sensor tests out good!!! What/where could the problem be?

[badjuju]

Hi all,

I recently posted a request for an ECU for a 1982 280ZXTand have since received one from World Auto Parts.

 

This might sound like a stupid question, but it's very important: do you have an 82 zxt? I ask because there are a lot of ECU swaps out there, and you might have read that this ecu works well in your z31 or something, which would explain any and all problems you have.

 

How did you test the sensor? How do you know it's good?

 

My 81 would run with almost every sensor disconnected.

 

Good ways to check the head gasket:

 

check the rad for bubbles while in runs - break between cyl and coolant

check the rad for oil - break between oil and coolant

check the oil for water - break between oil and coolant

when I said "white smoke" I meant something out of the ordinary. We all know what regular car startup looks like, I'm talking suddenly you see it and ask "what the f*ck is happening"

 

It's just steam from rad fluid burning off after being shoved into a combustion chamber.

 

take off all the sensordevice connectors (ie injectors and whatnot) one at a time, clean the contacts on the device, and on the connector, put the sucker back on. I bet you'll fix your problem.

[Guest Clarence A Wood]

I purchased the ECU from World Auto Parts and they insisted on a VIN number, I looked up the number on the ECU they sent and it is off a 1983. "How did you test the sensor? How do you know it's good?" I have the graph of temp to ohms so when I took an ohm reading it looked close. (I have since ordered an new sensor because the sensor ohm reading did not match what would reasonably be believed to be the actual temp of the head: I held a meat digital temp gage I use for barbecuing to the head and found over 30deg difference-not real accurate but the head is aluminum. ) The thing that puzzles me is why the engine just bogs down when the sensor is connected. It doesn't seem reasonable the 30deg difference would be that disruptive. But the book said that if the sensor (off of the head) does not match the graph when placed in boiling water to discard the unit, so maybe the ECU does some comparative logic that really aggravates a small diff into a severe response. A week from now I'll find out. I ordered the part from MotorSportAuto - would you believe that they held a discount on the books for over five years, which is how long its been since I've needed parts! Now that the engine starts correctly, the exhaust is clear for several minutes (5 maybe 10) and then turns white.

[Spraguepsycho1]

Sounds like just about the same time the cooling system would normally warm up and start pressurizing.