L28ET Running Issues

[destruck]

So I'm on the fence about this motor. I have gone through a lot of it already and am at the point of a pretty big choice. Opinions / thoughts gladly welcomed.

 

For starters this is a 70 240z with a full L28ET swap 82-83 harness, 83 motor, which is now running on a z31 ecu, maf and trigger wheel. Done so far?:

New Walbro 255 pump with a new return line to tank (restriction issues)

Aftermarket AEM FPR keeping fuel pressure at 30 with vacuum source

New cap, coil, wires, NGK BPR6ES - 11's gapped to .040

New timing components, and corrected motor timing

New o2 sensor

Boost leak check done

Vacuum leaks checked and corrected

Ecu was installed into a running car when I purchased it

Maf was tested against a know working one

 

Currently the car has a hard start issue, vacuum according to a autometer boost gauge is at 5. Car idles at 650-700 but is super rough, and upon revving while pretty much hit a wall at 2k-2.5k rpms. Here is a short video of what it is doing. This video shows high idle but once I did the timing it now idles much lower.https://www.facebook.com/photo.php?v=607430065989889&l=8886636705649794642

I have down a compression test which is as follows;

 

Reference - Cap of oil in cylinder

1: 135 - 160

2: 145 - 185

3: 145 - 170

4: 135 - 180

5: 125 - 160

6: 135 - 175

 

So I then proceeded to do a leak down test which shows cylinders losing 45%-60% through the dip stick.

 

My question is, will this low compression and bad rings lead to the problems I am having? Or could it be something else? Any input is appreciated, from here I don't know if it is worth it to pull it and freshen it up with new rings and gaskets or if it will still have the same problem.

[Enginerd81]

Compression doesn't seem like the culprit - I don't think the numbers are bad enough to cause what you are describing. 

 

Fuel flow test? I had a pump that I suspected was an MSD-2225 pump but wasnt sure. Measured flow before rail (unregulated) and after regulator (at 0psi, and 20 psi). To make sure it met specs.  I did this with a bike pump to apply pressure to raise pressure. Car not running.

 

Try putting your timing light on every spark plug wire to make sure they are all firing nicely.

 

Do mechanical and any vacuum advances work like they should?

 

How far up stream was the boost leak test done?

 

Clean the fuel injectors/try new ones? There are a few youtube videos for DIY or it's about a $100 to get it done.

 

Good luck

[destruck]

I have not tested the flow rate anywhere else, as the regulator has a gauge which I am using to verify no loss of pressure during idle or rev's. It did the same thing on the old stock pump as well as this new walbro unit. I plumbed a new return because it caused the pressure to rise to 50, but left the original feed hard line. I can try this if it is necessary even with the gauge on the regulator.

 

Pulled each plug and did the old spark on the block test, but using the timing light sounds like a better method to verify it with.

 

I am not sure if any of the vacuum advances work, or where they are on this car. It still has all the emission as far as I can tell as well.

 

Boost leak was tested at the turbo. Found a bunch of leaks on the intake, j pipe and almost every hose. Ended up replacing every hose on the car and making sure there was no leaks. Held enough pressure that the pop off valve released. No boost gauge at the time to verify what PSI.

 

We cleaned the injectors mildly, and verified they were firing evenly (and that all were firing) by eye. They held pressure, and none seemed to spray more then the other(on a shop towel). I actually thought about getting some spares to see if this was the problem.

 

I thought I should add, this car slowly progressed from running "ok" to not being able to rev over 2-2.5 over the period of a couple months. I was driving it when I first got it and it seemed to be running rich but other wise fine. Slowly it got to the point where it would not rev past certain rpm's starting around 5500 and then dropped to 4500, 3500 and now this. There was no tweaks or changes in between it just happened and I had no explanation for it. This is when I did the z31 swap because the afm tested bad and I thought it was the cost, but nothing changed at all, it still had the exact problem with the z31 setup now. The vacuum has been at 10 every since I got the car, and now has dropped to 5 after I did the timing (which was off).

 

Would a wide band help me with anything here? I have a down pipe ready to go on that has a bung already so I could put one in, but I don't know if it will be any help. 

Edited December 14, 2013 by destruck

[motomanmike]

A wideband will always help you more than not having a wideband.  Running the setup you are it would probably be your best friend at the moment. Good luck

[stravi757]

First I wouldn't bother with the wideband, yes they are helpful but Not needed in your case.

 

You said you have an 83 l28et swap, Then you mention your dry compression numbers which were good numbers for a turbo engine( I believe stock compression is 142psi). But then you showed a compression test with oil in your cylinders which jumped up to the compression of an N/A engine. Then you said you preformed a leak down test which showed 45%-60% leakage! Thats crazy high. Anything over 15% leakage generally suggests a problem that needs some attention. 

 

At this point I am convinced you have an N/A engine with excessive blowby(did you verify the leakage wasnt also coming out of the intake, exhaust, or head gasket?) If you have been driving it in this bad tune for some time now it makes sense why things have gotten progressivly worse for you. 

Your engine clearly needs some attention. I would fix your engine and go back to the stock turbo EFI. The 300zx set-up will just complicate things. 

Edited December 14, 2013 by stravi757

[destruck]

It's pretty much a weekend / fun car so 2 months of driving wasn't much at all. It seemed to get worse very quick. When I bought the car it was in bad shape, and with a little work it seemed to run good. 

 

I do not know the history of the car at all, it very well could be a Frankenstein setup. It is marked as a F54 / P90 that's all I know for sure. It is as far as I can tell a 82-83 motor and was running a 81.5 turbo ecu and AFM.

 

With the leak down it was verified only to be leaking out the rings, I actually was for sure it would be the head gasket but no bubbles in the coolant, and no leaks out the exhaust or intake. The numbers shown in the leak down test are what really got me and that's what I wanted to know if these two problems are related. At this point I have very well considered a swap since I have to pull the motor.

[cgsheen]

My L28ET has always run about 10-12psi of vacuum at idle (both stock and with VG30E engine management).  5 doesn't even sound close to right.  Find out why your vacuum is off.  Vacuum leaks make these engines run like crap and there are a few unusual vacuum components many people wouldn't see as potential problems - like the VCM as an example.

 

There is no mechanical or vacuum advance on these engines.  That's all handled by the ECCS.  Set your timing at 20 degrees and the ECU handles the rest.

 

What coil/ignitor are you using with the Z31 setup?  I have to say again that most of the problems with these engines come from wiring / electrical issues.  Check and clean all the connections and connectors - then do it again.  Verify that you've made the proper wiring changes for the ECU and MAF. 

 

You may need to start at the beginning - verify engine timing (chain / gears, oil pump / distributor shaft / rotor).  Then start with the engine electronics - which all starts at the CAS (yes, you can test it - if the procedure isn't in the Z31 FSM, download the 1990-91 Infiniti M30 FSM - same optical sensor & wiring the L28ET uses...).  Test every ECCS component and check and clean each of their connectors (both sides).

 

Remember that fuel pressure is a 36.3 PSI differential between the fuel rail and manifold pressure.  36.3 minus the vacuum PSI unboosted and 36.3 plus the boost PSI when running in boost...

[destruck]

Can the VCM go bad / fail? My vacuum use to be around 10 before I did the timing, but when I did the timing I found a hose that wasn't plugged in as well as the VCM wiring one of the two connectors was unplugged so I plugged it back in. I guess I could delete all this and see if ti helps?

 

At this point I can't even find the timing on the pulley anymore at idle, I'm not sure if thats because it is running so bad or something is off, but I will look into that some more. Timing has been corrected at the chain a friend and I put it back to TDC and where it should be with new timing components.

 

Ignitor is as far as I know a L28ET stock one, and the coil I just replaced with a stock 280zx turbo unit as well because the old one tested bad.

 

My next step was to actually dizzy and the cas sensor in the process because we thought that might be an issue as well but I will test it now that I know. I could not find a method of testing it before. Also planning to get some DeoxIT contact cleaner spray as it seems to work great by many members on here to clean up the connectors.

 

All this is really helping me hopefully I can figure this out and get her back on the road soon. Thanks guys.

[cgsheen]

The VCM can certainly fail. And there's a big rubber diaphragm in there to harden, crack, leak...  The FSM will show you all the potential vacuum problem spots if you look carefully.  You can delete the VCM but take care to plug or reroute all the vacuum lines involved.  It has a couple of connections to the intake chain IIRC, and controls both the A.A.C and the EGR with separate vacuum lines to each.

 

Normally if the engine mechanical timing is spot on, having the distributor set in the middle of it's adjustment range is close enough.  But you can always loosen that up and see what moving the distributor through it's adjustment range does to engine operation.  I found an L28ET that was off a tooth on the drive spindle by turning the dist. and seeing where it would run...

 

The CAS is normally a "go / no go" type of thing.  Won't hurt to test it for signal and while you're there check the chopper wheel and make sure none of the slits are buggered up.

[destruck]

If I do go ahead and delete the VCM, I will run a vacuum source to the AAC but can I do the same for the EGR or is it best to delete this as well?

 

It's raining here so I haven't had a chance to check the timing again but I still need to take a look and see what is up with it. I may have been rushing last time and just missed it.

 

CAS and wheel I will check, I found a crack on the distributor cap but it does not touch any of the contact points so I don't know if it effects anything or not.

[destruck]

Well, just a quick update.

 

The VCM was eliminated and the issue still persists. I unhooked the wastegate and it seems to still do the issue without any boost building as well. I did get a chance to spray some DeoxIT contact cleaner on all the plugs, and let me tell you, it made the car run so perfect. Idle is perfect, motor sounds so smooth now. However, my stumble / back fire is still there around 2k rpm's. I am going to try a known good set of injectors and next up is to check the whole harness from end to end.

[SDgoods]

Did you go through every damn test in the fsm?   

[destruck]

I've gone through everything in the FSM with no luck. I've got to go through it again because something is clearly wrong.

[malibud]

well I am curious now did you find the problem ? 

[destruck]

No luck yet. I took everything apart to delete all the extra smog / emission stuff to see if it helped. I am getting ready to make block off plates and put it all back together soon, I just let it sit since I picked up another toy in January lol. If this does not work, I will probably accept defeat and go sbc 350 carb.