78 280z flooding when starting

[Zed Head]

33 minutes ago, Dogariffic said:

 The tach was jamed at 2500 and this is standard. 

The first test was fuel pressure as I have the new online gage. Pressure was at 25. This is lower than the 32 at idle before we began the trip.

It's always at 2500 or it's standard for when the engine dies?  And did you power the fuel pump to get the 25 psi, or just look at the residual pressure?

Here's an old story I bring up sometimes - I've had my 76 and a 78 parts car both refuse to start when I had the tachometer removed.  The 76 also refused to start when the tachometer resistor fell out (I had unwrapped it from the harness just to get a look at it).  To me that would imply that if the tachometer circuitry was messed up enough inside that you could get a no-run condition.  It's an odd thing and the phenomenon went away after I switched to a GM HEI ignition module.  But it seemed like the quality of the signal on Pin 1 to the ECU must have been affected to cause it.  You could test your system by removing the tachometer inline resistor and seeing if your engine will start.  If it doesn't it's at least a possibility that the tach is involved.

Doesn't give you much direction but I suggest staying open-minded.  You have a weird problem so it might have a weird cause.

The GM HEI module swap is very simple, wiring-wise.  You can bolt it to any car part close to the coil, as a test, if you wanted to invest $25 and some time.

[Dogariffic]

Thanks, Zed.

The Tach has always worked to some extent.  When I first drove it to "test" before buying the car the tach worked normally as I remember. Then shortly after purchase, it would go to 0 with the ignition off and then only go up to about 2,500....even though the engine obviously was at a higher RPM.  

Previously when the car shut itself off doing 75 on the freeway the Tach dropped to 0. Yesterday is stayed jammed at 2,500.  After the restart, it worked normally up to 2,500 rpm again.

You asked if the fuel pressure at 25 was with the car running and this reading was just after the car shut off...a residual reading. Once it restarted it remained at 25 though.

This morning I read your note and went out to start the car and check the fuel pressure.....She immediately started but ran very rough, spitting and popping...very rough idle.  I looked at the fuel pressure and it was sitting at 40.  Over the past week and a half since I installed the gauge the pressure only went that high as the car was cranking to start.  Once she cranked the pressure always immediately....within two seconds....went down to 32 at idle.  I played with the throttle to smooth her out as she was spitting and popping and nothing worked to smooth her out until the fuel pressure began to drop....once it reached 32 she was running smoothly.

I plan to test the ECU more today and the fuel relays again and also take a look at the fuel pump.  This pump was with the car when she was purchased.  I have no idea how old it is. I will also test some more wiring and connections.

Curious of your thoughts about the pressure remaining at 40 after cranking and the car smoothing out once pressure dropped.

Thanks to you and the rest of the group!

[Zed Head]

37 minutes ago, Dogariffic said:

Previously when the car shut itself off doing 75 on the freeway the Tach dropped to 0. Yesterday is stayed jammed at 2,500.  After the restart, it worked normally up to 2,500 rpm again.

You asked if the fuel pressure at 25 was with the car running and this reading was just after the car shut off...a residual reading. Once it restarted it remained at 25 though.

This morning I read your note and went out to start the car and check the fuel pressure.....She immediately started but ran very rough, spitting and popping...very rough idle.  I looked at the fuel pressure and it was sitting at 40.  Over the past week and a half since I installed the gauge the pressure only went that high as the car was cranking to start.  Once she cranked the pressure always immediately....within two seconds....went down to 32 at idle.  I played with the throttle to smooth her out as she was spitting and popping and nothing worked to smooth her out until the fuel pressure began to drop....once it reached 32 she was running smoothly.

If the car was in gear and engine turning but the tach dropped to zero that's a sign that you've lost spark.  But there are many ways to lose spark, from complete power loss to everything to a bad ignition module.  It's one of those clues that you can build on.

Your fuel pressure probably stayed high when it was running rough because the intake vacuum was low because it was running poorly.  It was probably the other way around, pressure dropped as it started running smoothly.  Just a guess.  Trading cause for effect.

You're at the point where it might be worth your time to try an HEI module.  It's a good thing to know anyway because the old ignition modules fail on a regular basis.  It's just a matter of time before yours does, if it's not failing already.  You can get a BWD brand at any auto parts store for about $25.  That's what I'm using now.

I actually have an old 1978 module in the garage that I had wired in to my 76 for a short while, after my original module failed.  I don't know where Ridgeland is and don't know when I'd have time to package it up, but if you get in a bind I might be able to get it out to you.  But, long-term, it's just another old module on its last legs anyway.  Better to go with the HEI.

 

[Dogariffic]

Thanks Zed.

lets hold on the ignition module but appreciate the offer.

today we blew out the fuel return line in case that was the cause for high fuel pressure. Then looked at the fuel pump. It is a  Carter so not original and it does not have a filter screen I can access. There has need an inline filter prior to the fuel pump since before my son bought the car though. We had the gas tank cleaned FYI but stuff keeps coming out. Change the inline filter monthly.

took fuel pump out and blew through it then reinstalled.  Car started and idled so we took her out. She cut off 5 minutes later and we were able to coast home where she immediately restarted.

fuel pressure was 30 and the fuel pump was not leaking and was not hot. Tach locked at 1500.

Now looking at the ignition module as a solution.

 

 

[Dogariffic]

And as a follow up z....

i planned to reopen the ECU and started the car. She idled well and I reached down and wiggled the ECU. The car almost stalled so I wiggled it back and she smoothed out some.

we then took the ECU out and opened it up again looking for something. We checked every connection and path with a monitor and all of the connections checked out. 

But obviously we have isolated something that causes the car to have a rough idle and over fuel. 

Now how to fix it.  I have seen you can send these boxes off to be rebuilt. Anyone ever done this? And who did you use.

i will also search threads for this info.

[Zed Head]

Here's a good thread and its link.  

 

[Dogariffic]

Thanks again Zed.

i read the threads. So is it really as simply as soldering the places that are already soldered? Front and back.??

after looking at the board closely I really can't see anything broken, burned or disconnected. I do see what looks like glue around a few solders that is discolored and hard to the touch. 

Rather than seek each broken connection I may just resent-solder them all again. May seem like over kill but at least I won't miss one.

good idea??

[Zed Head]

It works for some people.  It doesn't work for others.  That's why we collect old parts.  Some people have found the loose connections in the connector, not the ECU.  Peel the rubber seal back and check the connector.

[Dogariffic]

Appreciate all of the advice. Here is an update.

Purchased a Crane or now FAST xr3000 to replace the ignition module which looked to be failing. During the install process I noticed a loose piece of metal in the stock distributor. It turned out to be one of the centrifugal vacuum advance weights. It had broken loose.... photos to come. 

Thought this might be the reason she shut off driving 75 on the highway.... loose metal touching something....anyway bought a rebuilt distributor and got it on.

She started and ran well, but different. Different idle and feel... not bad , better.

But she still failed After she got hot on the highway. But this time she was at a friends garage when she failed. The ignition module box was too hot to hold so we cooled it and she started right up. I then installed the Crane xr 3000 and again she started right up and drove really well.

Cut her off and gave everyone a high five. Got in to drive some more and she would not start.

Eventually got her started but with rough idle and she kept trying to stall as if flooding. While I kept her running another person opened the AFM and it moved appropriately. He then pulled the throddle sensor wire clip.... which is new 4 months ago by the way..... and she cleared up idling smoothly. But she won't start with the sensor unplugged.

After letting her cool off about 5 hours I started her up. She coughed a bit initially and she ran like a scalded dog.

So it looks like it is the throddle sensor, or the ECU reading the sensor or possible the AFM.

Working to test more!

Thoughts

 

[Chickenman]

Haven't read the whole thread, so this may have been covered already. But one of the essential things to do is get a can of GOOD electrical contact spray such as De-Oxit or Weicon and spray every single electrical connection. De-Oxit and Weicon will literally clean mildly corroded contacts to as New condition with one or two applications. Heavy corrosion such as hard scale, may have to be scraped off with a Jewelers screwdriver or dental pick. 

If you have a electrical connection that alter how the car runs when you " wiggle " it you either have  corrosion on the terminals ( doesn't take much ), a broken wire in the terminal or some other form of bad connection. 9 times out of 10 with these Vintage cars it is corrosion. They didn't use WeatherPack seals back then like Modern cars do.  The TPS, all the coolant sensors on the Thermostat housing , AFM connector, all the Fuel injector terminals and ECU connectors should all be examined with a Magnifying glass and meticulously cleaned. Bad terminals should be replaced. Check all the ground wires for  corrosion, frayed wires or loose connections. Take the ground wires off and sand the contact area beneath to bare metal

Bad grounds will overheat components and cause them to fail. 

1 hour ago, Dogariffic said:

The ignition module box was too hot to hold so we cooled it and she started right up. I then installed the Crane xr 3000 and again she started right up and drove really well.

This is a big RED flag. The Trignition box should NOT be getting that hot. Could very well  have been a bad ground causing it to over-heat. Now you replaced the Trignition Box with the Crane unit. The Crane Unit has it's own separate ground. So you may think that a poor ground issue to the original Trignition box is now redundant. Not so fast. Ground circuits in engine harness's are often shared with several different components. I'd have to look at the wiring diagram, but it wouldn't surprise me if the ECU, Trignition,  AFM and some other sensor share a common ground. In fact, that is a SOP to ground all the sensors through the ECU through and to a common ground point to reduce voltage offsets. 

Making sure that all grounds are 100% should be done to eliminate any variables.

 

 

 

 

 

[Chickenman]

Interesting little story;

Had a friend whose 280Z was running intermittently and badly. She had just paid a local Shop big $$ to go over the complete EFI system. They had replaced the ECU and supposedly, " cleaned " every single electrical terminal on the engine harness.  There It was.  Marked right on the Work Shop order. " Clean and service electrical connectors -  $250 labour "

Indeed, I did find that every single connection was packed with brand new Dielectric grease.. Unfortunately they had not bothered to scrape off the old corrosion first!!! I couldn't believe, it but I found several connections with obvious green scale visible through the Dielectric grease.  Including the CTS and AFM connections.  Several of the injector terminals still had obvious corrosion visible if you looked closely as well. Idiots!!.

I re-serviced her car in the local Canadian Tire ( CDN GI Joes )  parking lot. Two cans of Brake Clean ( to remove superfluous Dielectric grease ),  Much scraping with a Jewelers screwdriver, a spray treatment of De-Oxit  on every single engine harness terminal, some fresh dielectric grease.... and a free lunch from a very happy Lady whose car now purred like a kitten and has not had a single " hiccup " in over a year. It's the details that are important....   

[Zed Head]

3 hours ago, Dogariffic said:

But she still failed After she got hot on the highway. But this time she was at a friends garage when she failed. The ignition module box was too hot to hold so we cooled it and she started right up. I then installed the Crane xr 3000 and again she started right up and drove really well

 

While I kept her running another person opened the AFM and it moved appropriately. He then pulled the throddle sensor wire clip.... which is new 4 months ago by the way..... and she cleared up idling smoothly. But she won't start with the sensor unplugged.

After letting her cool off about 5 hours I started her up. She coughed a bit initially and she ran like a scalded dog.

So it looks like it is the throddle sensor, or the ECU reading the sensor or possible the AFM.

Somebody actually reached up by the fuse box to touch the ignition module, to see if it was hot?  Just want to be sure you were looking at the right part, or don't have an aftermarket setup already in the engine bay.

The thing with the throttle valve switch (should be TVS, but people use TPS) is interesting.  Maybe that's the circuit in the ECU that goes bad and causes ECU problems.  Weird that it wouldn't start with it disconnected though. I think that should show the ECU the position between idle and full throttle, so just a little less fuel than at idle.