1977 280z possible EFI Problem?

[ckurtz2]

Hey Guys, 

        I hate having to post in the fuel injection section of this forum, because I hate EFI issues, but here we go. I will try to be as detailed as possible.

        As you know I have had some EFI issues in the past, but I got them all sorted out about a month or two ago and my car was running near perfect. In the past two weeks I have been having an issue where the car will either surge at idle, buck hard under part throttle or hit essentially a rev limiter. Happens damn near randomly, except it has definetly been getting worse over the past few days to the point where it is undriveable as of this morning.

       I first noticed it about two weeks ago in Arizona traffic in the hottest part of the afternoon. Out of nowhere the idle fell from about 1200rpm(yes Ik its high, I have since resolved this issue) to about 300 then it caught itself and went back to about 1500, and then just did this repeatedly. And then it just randomly stopped and I was good to go. Next time I noticed it, I experienced the same thing. I was idling at a car show in line for a long while and poof idle randomly fell. When it falls it's extremely abrupt like my fuel pressure goes to 0 or spark is cut entirely, then it would catch itself and shoot way past my set idle speed and then fall again, and then randomly smooth out. After this happening for a few minutes I was able to leave the car show and I WOT onto the highway entrence and about the biggest cloud of smoke came out the tailpipe that I have ever seen (grey).  Then about ten miles later on the highway the car would loose all power under any throttle input for about 2 seconds (RPM on tach stays the same) and then catch itself and be fine. 

      Next time I noticed it was a few days later. Started the car, it warmed up and immidiately it sounded weird. Gave it a rev and it popped big out the intake, AKA super lean. Ok, turned off car, started it again and the problem immidietly dissapeared. The next day I started it cold and it started rythmically popping out the exhaust, big booms out the back under part throttle. So now it was being super rich. Restarted the car and the problem went away again.

      Now in the past week when I drive it around the block (trying to figure out when the problem is occuring) it will surge at idle only sometimes(rarely now) but under part throttle it either bucks like all hell or hits what seems to be a rev limiter.  So as you can see it's been a little impossible to diagnose as symptoms change almost what seems like daily. The car bucks like hell warm or cold now. It also struggles free revving.

The tank is rust free, new spark plugs, new injectors, new fuel filter, etc etc. 

I watched the fuel pressure at idle and its a steady 28psi, under throttle it raises as it should. 

So I am at a complete loss if this is a spark problem or fuel problem.

Luckily the the problem was consistent enough today I could pull out my phone and snag some videos. You can see that the car bucks badly, and hits a rev limiter. All of this was recorded at the same throttle input (1/4 throttle or less). I got it to rev up without cutting when I matted the pedal. As you can see it's like riding a bull. 

https://urldefense.com/v3/__https://youtu.be/12XZ2cdfsO0__;!!IKRxdwAv5BmarQ!fE9nrDYKDsfg3pQMI3nISyNOzjJOgfXGtS6ZOtQ11qQhDp_XGhAh6wzW5KRg0tbBiD28vwXgz6ChP2MZ1ASj2SoX$

https://urldefense.com/v3/__https://youtu.be/AhmiXD09NwM__;!!IKRxdwAv5BmarQ!cbEdNrHLCcm69RgNO5EzHkIZL9xu_zTAcNqN4yUP8151vyGAxeI0EW-ffHhFaQ7WDQLLbCZJ_xSxxEU3Y_GstqcP$

Is this a typical issue of a failing ECM or Trignition Module? Out of all the forums I have read I can't get a lock on if it is.

 

 

  

Edited September 25, 2022 by ckurtz2

[kickstand80]

Clean the connections on the AFM and the engine temp sensor that goes to the ECU. Check all the connections, ignition, injectors ect. Make sure they are clean and tight. Check the function of the distributor advance, check to see if the bearing retainer in the breaker plate is broken. A crack in the distributor cap. A bad points condenser if you are running points.  Random issues are the hardest to diagnose. 

 

[TomoHawk]

Thast's not an issue.  It's a problem. There is a difference. Please learn to use correct English, not liberal  jargon.

[Zed Head]

1 hour ago, ckurtz2 said:

Is this a typical issue of a failing ECM or Trignition Module?

The richness and erratic running kind of fit what's been reported for a failing ECU.  I had one fail as I was testing it, but it just died completely as I was road-testing, then restarted after a few seconds.  It did this about three times before it wouldn't restart as I tried to get home.  I was about a mile from home.  The exhaust smelled like fuel as I tried to restart it at the end.  I ran home and got the original and the engine started right back up and was fine after that.

Anyway, short answer, people have had luck diagnosing it by banging on the side of the ECU or wiggling the wires to it as the problem is happening.  If the problem clears up then you know it's in the ECU.   Apparently the problem is caused by broken solder joints.  People have had luck reflowing them, I didn't try on mine.

 

p.s. since the "problem" is fairly common it can be defined as an "issue".  That's just how words work.  "The issue under discussion  is the common EFI ECU problem".

https://dictionary.cambridge.org/us/dictionary/english/issue

 

[ckurtz2]

51 minutes ago, TomoHawk said:

Thast's not an issue.  It's a problem. There is a difference. Please learn to use correct English, not liberal  jargon.

As per google: Issue- "an important topic or problem for debate or discussion".

Don't let politics win. Issue is what it means, not whatever politics says it is these days (if that's what you are referring to as liberal jargon). Problem or issue could be used synonymously here. 

In hopes that you actually cotribute to the conversation. I will change the title.

@Zed Head

Thank you. I am going to run through the FSM on Wednesday for EFI and see if anything new comes up. It seems hard to test electrical as most of the FSM wants you to use an oscilloscope, which I don't have. Really don't want to shotgun buy parts on this one. Also let me know if the duplicate post was removed on your end. I think I was able to get rid of it.

 

Edited September 25, 2022 by ckurtz2

[Zed Head]

The other thread seems to be gone but so is @siteunseen 's post that was in it.  Oops.

The test for the sporadically bad ECU problem is to bang on it.  I don't think that it will show up from the Nissan test procedures.  It might show up on a scope if you had one.  That's the big thing at the small repair shops on the Youtube channels, they have scopes that they can take with them as they go for test drives.  Pretty cool, but takes some money and know-how.

Edited September 25, 2022 by Zed Head
The @ thing didn't work, had to retry

[ckurtz2]

@Zed Head

I have his post locked down in memory. The switch, connector, and bullet connectors are all new. Working as should.

I wanted to see if the AFM had anything to do with it. So I cleaned the inside carbon trace. When it was running I hald the vane still, so that it would not rise and fall with the bobbling RPM. The idle still continued to surge. I really feel like the AFM is just fine, and I know the CTS sensor is fine. I also agree that I don't think the usual Nissan diagnostics are going to fix this one, but I am going to do it for peace of mind. I also wanted to mention my CTV and BCDD was deleted from the system. I just filled all the ports for the BCDD with RTV and then put the block off plate on.

Funny to mention hitting th ECM. I did multiple times and got no result (they weren't very hard hits as I don't want to ruin the module if its actually fine). I almost wonder if it's cutting spark. However, this wouldn't make sense in the other videos where it looks like I was hitting rev limiter. As the car would have just died if spark was cut.

Here is a video of the idle problem. I actually held the throttle a little open to exasterbate the issue. 

 

[Captain Obvious]

Well that looks unpleasant. I can't tell from here if it's specifically electric or fuel, but certainly unpleasant.

Based on the behavior of the tach, it doesn't appear to be a problem on the primary side of the ignition system. By that, I mean, it does not appear to be related to the ignition module or the ignition switch. It could still be something on the secondary side like coil, cap, rotor.

I would check that sort of stuff and also check the condition of the electrical connections between the battery and the EFI system. There are two large spade connectors and a fusible link that come off the battery and are dedicated only to the EFI system. Take a look at those.

Here's hoping it something simple.

[ckurtz2]

@Captain Obvious Yes, unpleasent is the kind way of putting it.

EDIT** I went through the ole EFI bible and realized the even the EFI is controlled by the ignition. The coil sends the signal to the ECM and then the ECM does its magic with grounding the injectors. Just tested my coil. Primary windings tested 0.6-0.7ohm. Secondary was around 9.6kilo ohms. So all seems fine there. Wires hooked up in right order. Blue wire from the resistor to negative coil terminal, black and white to positive coil terminal. Not sure if a coil can intermitently fail.

I will definetly make sure the fuseable links and those grounds are good when I work on the car Wednesday.

Rotor seems perfectly fine. Cap seems fine. There is a possible microcrack in the cap, but it is hard to tell. I did resistance test all throughout the cap, and it all tested out as should. No terminals were continuous with eachother.  As you can tell the crack is super small. I couldn't see how this could be my issue. As I would assume if the cap was bad it would be a constant misfire, not bobbling rpm like power keeps cutting.

Edited September 26, 2022 by ckurtz2

[Captain Obvious]

Yup, low side of the the ignition system triggers both the tach and the ECM (as well as the coil). But since the tach seems to be working without an issue (even when the car is bucking) I'm thinking the low side of the ignition system is OK.

And yes, coils can fail intermittently, but there can be other things at play... It might not be a hard black-n-white fail kind of thing. It might be a failure that presents itself above a certain RPM range. Or it might be engine load related since it's more difficult to spark a plug when there is a more dense mixture in the cylinder.

Sparks that travel just fine at idle might jump somewhere they don't belong at higher engine loads or RPM. That kind of thing. I'm not expecting a dead short in the cap. Certainly nothing you would measure with your typical VOM.

When you get a chance, take a pic of the EFI connections at the battery to make sure you've identified the right wires.

Not saying this is electrical, but it's an easy place to start to rule stuff out.

 

[Mark Maras]

I don't have an answer but my first impression is it's not electrical. Seems more like the throttle butterfly is opening and closing to produce that amount of variation in the rpms. It appeared that you were holding the throttle steady.

[jonathanrussell]

Your problem sounds similar to what I experienced with my 75 280 a few years ago. The AFM flap was stuck open....because it was slightly bent. It probably got worse and worse due to repeated intake backfires.

Something to check out....

 

And...all...is it really that necessary to take a stand on a person's use of one word or another? That kind of comment just seems out of step with the purpose of this forum and also the typically kind culture I see here. Lets leave that stuff out of this great site.