Working hard, but still have a flooding issue. Looking for advice.

[Pillar]

Hello all!  I know this is a lot to read, but I am trying to be thorough and give as much info as possible.  If you don’t want to read it all, you can skip to the last few sections and get the general idea of my current issue that I need help with.  Thanks in advance!

 

 

First, a little about me/the car: 

 

I have worked on cars for about 13 years now.  I don’t consider myself a pro, but I consider myself fairly knowledgeable when it comes to cars.  I have rebuild motors, help friends restore cars, done motor swaps, and do all my own maintenance.  However, I know that every car is different and comes with its own unique issues/methods, so there is always something to learn.  I bought a 76 280Z about a year ago and have been slowly fixing it up.  This is my first Z so I knew it was going to be a learning experience (which is what I wanted) and so far I feel that I have done quite well with it.  It was in pieces when I got it.  The previous owner had blown the head gasket and had decided to take the opportunity to throw in a Chevy V8.  He got as far as striping everything out of the engine bay and then decided he wasn’t interested.  Luckily all the parts were there (albeit in many many boxes) so I decided to jump on it.  I picked it up for cheap since it was an unassembled puzzle that needed some work.  I decided to rebuild the stock L28 and put everything back in.  I have completely dissassembled, cleaned, and powdercoated the suspension.  There was a little rust in the usual places, but I have gone and cut out/fixed all of that.  The interior was mostly bare and I have been working to fix it up.  I will be posting up some pictures of the work before/afters of what has been done so far.  This is in no way a full restoration project.  The goal a solid project car that will be fairly reliable and I can drive every day if I want.  I am trying to keep it a budget build so I have been doing all of the work myself (aside from machining the block and head).  I am in the final stages of getting it back on the road, but have run into a big issue.  Before I get into the issue, let it be known that I have had the FSM and FI Bible for it since day one and have been over them many times throughout the build.  I have done searches on the forums but have only found one other post that had similar problems and so far, doing what that person did to fix the issue has not solved the issue on my car.  I have tested just about everything I can using the FSM and FI Bible (and I will go into some more detail about that), but have been unable to solve my issue and I am ready to farm this out to the Z community for any suggestions and advice. 

 

 

The problem is as follows:

 

When I first got the motor back in and everything hooked up, it would start fine and idle decently, but had a bad misfire under acceleration and once warmed up real good, would occasionally sputter and die at idle.  The severity of the rough idle/acceleration seemed to vary quite a bit over the coming weeks trying to diagnose and fix the issue.  I adjusted the ignition timing and it seemed to help a little but it did not completely solve the issue.  I installed a fuel pressure gauge in line (was planning on doing that anyways) and it shows normal pressure as described in the FSM.  I pulled the plugs (which are new) and they were covered in soot, so I know that it was running very rich.  I figured that it could be sticky injectors (the only thing aside from the pump that I didn’t change in the fuel system) so I went ahead and swapped them all out.  I was able to get a new set of Bosch injectors on a closeout price so it wasn’t a big expense and probably would have needed to be done anyways since the car sat for over a year.  Still ran rough.  In the past month or so (I have a very busy schedule during the summer so progress has been a bit slow) I have accumulated only a few miles from taking it up and down the driveway and around the block once to test out whatever adjustments I made.

 

Currently the car will not start (yeah I know, you’ve heard it many times before in the “my car wont start please help me!!!” posts).  It all started when I last took it down the road for a test and then after the motor was good and warmed up I turned it off.  When I went to crank it up again after about 2 minutes it started briefly for about 5 seconds and then died.  I cranked it again to try to start it and would get nothing.  I popped the hood to have a look and saw fluid pouring out from near the radiator.  I thought “crap, busted the coolant system”.  I go forward to have a look and realize that it is fuel pouring out of the intake filter.  You can imagine my alarm when I realize I have a ton of gas pouring out of a hot engine!  I let the car cool down and started the process of evacuating the fuel out of the cylinders/intake.  The car will no longer start at all, it will just immediately flood. 

 

 

On to what I have done to try to fix the current flooding issue: 

 

I searched the forums for  stuff like “fuel coming out of the air filter” and was only able to find one really closely similar post, found here: 

http://www.classiczcars.com/topic/43951-1978-280z-fuel-pouring-from-throttle-body/

Reading through this lead me to the common “bad CSV” issue.  I have since blocked off the CSV entirely and yet it still floods.  I have hooked up a set of noid lights and cranked the motor (with fuel pump unplugged of course) to test that the injectors were getting a pulse from the ECU instead of being stuck on, and they were all fine. I tested the AFM directly with a multimeter and it checks out.  I tested the main connector to the ECU and everything checked out within the specs lain out in the FI Bible with one possible exception.  The page for “Air Flow Meter Fuel Pump Contacts” (page 53, Test #1-(5)).  It says when the AFM flap is at rest there should be no continuity, and that when it is open there should be continuity.  What it doesn’t say is whether or not this test should be done with the key off, or in the on position (some test state to have the ignition in the on position, while others do not).  When I run this test with the key off, it checks out fine.  But when I run the test with the key in the on position, I get continuity all the time regardless of flap position.  If I understand the system correctly, this circuit is what keeps the fuel pump running when the engine is running, and shuts it off when the engine stops running.  So to me, I would think that this test should still have no continuity with the flap at rest and the key in the on position.  Is this correct? If so, I feel that it might be that the AFM is bad, but when I test the AFM directly with the multimeter, it seems fine.  I just don’t want to start replacing very expensive items to diagnose.

 

Clearly something has changed after the first time it flooded out because that is all it will do now.  I was thinking maybe the first time it flooded, gas got into either the AFM or TPS or something, and is causing a short or false signal and telling the ECU to pulse longer than it should, or pulse at the wrong time.  I opened up the ECU and it looks perfect (no bulging components, no burns, clean as a whistle).  Since the last time it flooded, I have dried everything out and completely disassembled and cleaned the BCDD (which was full of fuel).  I did a compression test again and so far it looks like no mechanical damage has been done as a result of flooding the motor a few times.  I cant find anything wrong (and it could be that I am missing something), but I am reluctant to keep trying to start it because of the clear risk of causing mechanical damage if it keeps flooding.

 

Sorry again for the extremely long post, and thank you very much if you took the time to read through it all and reply.  I tried to be thorough, but in my long post may have left something out.  If so, I apologize and will add info as requested.  Any help or suggestions would be greatly appreciated!

 

TO RECAP: 

 

The engine used to run, but misfired and was running very rich.  One day it flooded out to the point of fuel dumping out of the intake and now that is all it will do.  I have tested the AFM and ECU harness and as far as I can tell it all seems to be pretty good.  Parts that are new are the injectors, ignition coil, plugs, FPR, fuel filter.  I get spark, and fuel pressure is good.  I have blocked off the CSV entirely, so it is safe to say that it isn’t what is dumping fuel into the intake.  ECU looks good and I have tested each injector plug with a noid light and am getting a pulse.  It could still be that the ECU is sending a longer pulse than it should, but I don’t have an extra ECU around to see if there is a difference.

[NewZed]

I wrote a while thing about injectors then realized that the most likely suspect is your FPR.  It's blown and allowing fuel through the vacuum hose when the pump is running.  Try disconnecting the vacuum hose and see if fuel comes out when you recreate the issue.  I also get the impression that your pump runs all the time when the key is On, and may have been rewired.  So the intake manifold would start receiving fuel as soon as the key was On.

 

 

If it's not the FPR then consider this:

 

The injectors would only stay open if they had a short to ground on the ECU side.  You said that you "get a pulse" with the noid light but what does the light do when the key is on but the engine's not turning?  IT should be completely off.  Describe the "flooding".  Does it fill with fuel if the key is turned on and left on, or only when the engine is running?  The first would be a short, the second could be too many ignition pulses or overheating in the ECU.  How long does it take to get lots of fuel?  Seconds, minutes, or many minutes?

[Pillar]

Thanks for the ideas NewZed. I have gone over things so many times in my head that I feel it is getting all muddled up. It is nice to have a fresh mind to help me troubleshoot

 

Good point on the FPR. The FPR is new, but I will still double check that.

 

I did think that it could be that the pump is kicking on early due to the AFM Fuel circuit test I did, but I don't hear the pump kick on and fuel pressure does not go up with the key in the on position.

 

The engine does not flood with the key in the on position either (at least not nearly as fast as cranking it). It only seems to flood when I crank the motor, but I will leave the key in the on position for a while and see if it floods after a longer period of time. When I do crank it, it floods quick enough that it won't start. The first time it flooded out it had started for just a few seconds and then cut of. About 10 seconds of cranking was enough to fill the manifold.

 

I also hadn't though of testing the injector pigtails with the noid light while the key is in the on position and not cranking. I will try that as well.

 

Thanks again! I will post my results.

[NewZed]

Overfueling or flooding is one way that ECU's die.  Could be the injector transistors are shorted, or, apparently, the solder joints at the cable connection point.  People have had a milder case of the problem (running way too rich) and fixed it temporarily by beating on the side of the ECU or wiggling the main cable.

 

I had one die while I was test-driving the car and the guy that helped me push it off the road said he could smell a lot of gas.  It died and restarted about three times then died for good, before I pushed it off the road.  Ran home and picked up the good ECU, swapped it in and drove home.  I put new transistors in (not direct replacements, just an experiment) and it worked.  Just an aside.

 

Several people have reflowed the solder joints at the connector and fixed a similar problem.

 

Anyway, if you confirm that the injectors are dumping too much fuel only when they're getting the signal from the ignition system (engine cranking or running), odds are it's an ECU problem.

[Phantom]

I had an issue with my '77 running richer and richer until I was down to 5.5 MPG and my plugs were wet with fuel.

What I found out is that I had corroded aluminum bullet connectors in the engine temperature sensor harness and the ECU was getting an "I'm cold" signal all the time and running the engine very rich.  It also had the cold start injector running most of the time.

The ETS is located in your thermostat housing.  Follow the wires in the harness about 18", give or take, toward the firewall.  You should be able to see/feel a fat spot in the wiring harness.  Cut away the insulation and you'll find the connectors.  Pull them apart, clean them up, coat them with dielectric grease and reassemble and see if that helps your problem.  I did that and my Z started getting 18-20 MPG right away.

Edited June 6, 2015 by Phantom

[Pillar]

NewZed, you hit the nail on the head with the FPR. I disconnected the vacuum line and jumped the fuel pump, and sure enough I got a steady stream of gas out of the vacuum side. It is a brand new FPR, so it was pretty low on my list of potential problems, but once you said what you thought might be the issue, it clicked in my head immediately as making a lot of sense and sure enough you were right. Thank you very much!!!

 

I am still going through and testing the rest of the fuel system just to be safe, and I plan to check the return line for blockages just in case something came loose in there and caused a pressure spike that blew out the diaphragm. I will be sure to post once I have it running.

 

Again, thank you for the help!

 

Cheers