77 l28et swap super rich 10-12 mpg

[alexx933]

Hey, so I finished my mostly stock swap a couple weeks ago and have driven it around 700 miles now. I changed the oil and water yesterday at just over 500 miles. Here is my page that I was asking questions with if you need any background information: http://forums.hybridz.org/topic/112637-help-for-stock-l28et-swap-into-a-77-280z/

 

My problem is that I'm only getting 10 mpg. I'm pretty sure that something is off. This motor should be getting at least 18-20. I measured the mileage yesterday with some mixed driving and only got 10 mpg. Today, I changed the corroded O2 sensor (thinking that might help) before I drove 50 miles out and back on the highway. I was able to keep a fairly consistent speed and only passed a couple times because the trucks were going 10 under. I left from the pump 50 miles and came back the same route 50 miles to the pump. I filled the tank with 7.687 gallons for exactly 97.4 miles for 12.67 mpg. Not cool...

 

As I took off from a rolling start in second, a bunch of black smoke went out the tail pipe when the boost hit. I repeated this later on to make sure it wasn't a fluke. 

 

There could be a couple things wrong that I haven't been able to pinpoint yet. Too much fuel pressure? I have the fuel pump hooked up from the on switch through an inertial switch. Could that be giving it too much voltage causing the pump to send too much fuel? When I hooked the pump up, I checked the fuel pressure to be about 35 psi. 

 

The EGR is also connected but has no vacuum at all to the valve because I plugged it. Would hooking the EGR back up to the VCM contribute to higher mileage? I've heard and read mixed reviews about the EGR system.

 

Any other ideas?? 

Edited June 5, 2013 by alexx933

[NewZed]

The engine wouldn't even run in the last post in your link, now you're driving it.   Open the ZX FSM that fits the year of your engine and go through the troubleshooting in the EF&EC chapter.  Check the CHTS circuit first.

[alexx933]

I just meant the link to be as a general background and this post for more specific information. I'm looking through the FSM now. Hopefully I can turn something up. Thanks!

[NewZed]

Good luck.  There's a third of a page dedicated to "Poor gas mileage".  EF&EC 18.

[alexx933]

Which year FSM are you using? I've checked the 82 and 83 but can't find the "Poor gas mileage" you are referring to. 

[NewZed]

I opened up the 81 FSM, but it looks like Nissan changed things in 1982, to focus on the ECCS analyzer.  Probably worthwhile to look at the 81 just to get some ideas.  Nissan tried to make things easier but just made them more complicated instead.

[rayaapp2]

I was able to achieve 24mpg city and 29-30 hwy with an early 260Z L28et swap and 22mpg city 29mpg with a stock 83 280zxt 2+2.

That said, I would also start with the FSM diag.

Fuel pressure,CHTS, TPS, and MAF would be my first things to look at if it is properly wired. There are plenty of things that can be mis-wired like the start signal that would cause this issue as well.

O2 has little affect on AFR. For these old cars Id pull the sensor out of the exhaust during diag of a car thats running like that. Your more likely to foul the sensor like that.

[alexx933]

Alright, so fuel pressure was 30ish at idle and 35psi with throttle. I didn't mess with the Air flow meter. The TPS seems to be working as it should. I unplugged the CHTS while it was running which killed it as it should. The two wires from the EFI harness that connect to the thermostat housing are both plugged in now. I took one off so I'd have a working guage. I also ran a vacuum line from the VCM to the EGR. After I did all that, I drove around for a bit. With the guage reading about 3/4 of a tank, I've only driven 45ish miles. That's still low mpg (45miles/3ish gallons). When I refill, the exact measurement will be posted. 

[rayaapp2]

Shooting in the dark probably wont help you much. Follow the FSM procedure and you will find what issue/s are messing with you.

 

Ray

[cgsheen]

Alright, so fuel pressure was 30ish at idle and 35psi with throttle. I didn't mess with the Air flow meter. The TPS seems to be working as it should. I unplugged the CHTS while it was running which killed it as it should. The two wires from the EFI harness that connect to the thermostat housing are both plugged in now. I took one off so I'd have a working guage. I also ran a vacuum line from the VCM to the EGR. After I did all that, I drove around for a bit. With the guage reading about 3/4 of a tank, I've only driven 45ish miles. That's still low mpg (45miles/3ish gallons). When I refill, the exact measurement will be posted. 

 

Read the FSM.  Fuel pressure is not a static (constant) value.  The FPR should maintain a 36.3 PSI differential between fuel and manifold pressure.  If your manifold pressure is -10 PSI (10 PSI Vacuum) at idle your fuel pressure should be around 26 PSI...  In boost it should be greater than 36.3 PSI by the amount of boost pressure (ex. 6 pounds of boost should mean fuel pressure of 42 PSI).   It should change continually as you drive because the manifold vacuum (and boost) will always be changing.  If you have a "boost gauge", watch it as you use your right foot and you'll see what I mean.

 

That's not likely to be your problem - or at least not entirely.  +1 for running through the simple testing procedure in the FSM.  "TPS seems to be working" ??  Very easy to test with an electrical meter - even a $4 Harbor Freight meter...  It only has TWO positions that an L28ET ECCS cares about - open or closed.  How to set it and check proper operation is in the FSM.  So are the Ohm values for a properly working CHTS - unpluging it to see if the engine dies isn't the proper way to test. 

 

The other two temperature sensors in the t-stat housing have absolutely nothing to do with engine operation.  One is the temp sender for the cockpit gauge - doesn't send any info to the ECU.  The other is a thermotime switch - on the L28ET it is only used for the "hair dryer" - the aux. cooling fan - and also has nothing to do with the ECCS (on a stock 280ZXT, it cools the injectors / intake after engine shut down IF the water temp is too hot at shutdown.  Vapor Lock.  Never active when the engine is actually running.)

[stravi757]

Alright, so fuel pressure was 30ish at idle and 35psi with throttle. I didn't mess with the Air flow meter. The TPS seems to be working as it should. I unplugged the CHTS while it was running which killed it as it should. The two wires from the EFI harness that connect to the thermostat housing are both plugged in now. I took one off so I'd have a working guage. I also ran a vacuum line from the VCM to the EGR. After I did all that, I drove around for a bit. With the guage reading about 3/4 of a tank, I've only driven 45ish miles. That's still low mpg (45miles/3ish gallons). When I refill, the exact measurement will be posted. 

 

Just because the engine died when you pulled the chts still does not mean the sensor is functioning properly. While it does indicate the sensor is giving some sort of reading to the ECU, it does not mean the reading is accurate(the sensor needs to be tested). Like mentioned multiple times above. Your best bet is to read through the FSM. Its really tough to say what you problem is with the information your giving us. The FSM does an amazing job of explaining each sensor and how they work. Im sure it will answer most of your questions. I canot stress this enough. If you read through it to help diagnose your problem and still cant find out whats wrong. I bet you will atleast know much more about your engine and be able to direct us better in helping figure out whats wrong.

[alexx933]

Alright, sorry for some half assed info guys. I was really hoping i wouldn't need to take my intake off because it's a pain in my ass. But I looked through the 81 FSM which has the poor mileage section, it shows the ECCS as being a single plug. However, my harness uses three plugs. By finding the correct pins, will my continuity testing reveal the same results?

[NewZed]

In your case, the 81 troubleshooting chart is only good for ideas about how things work and some cause and effect clues.  81 had a separate Turbo Supplement that describes the three plug ECCS.  The main 1981 FSM is for the 35 pin style ECU.  The concepts are the same though.  Sensors provide information that the ECU or ECCS computers use to determine fuel enrichment.

 

Pretty sure that after the whole ECCS analyzer section in the EF&EC chapter there is some basic multimeter testing that you can do.  You just have to work through the whole chapter.  Take notes on where the good stuff is.

[alexx933]

So after a long break, I've decided to figure this out once again. I began with the 81 FSM in the supplement section EF. From there I was going to test everything with the assumption that my perpetrator would be either the TPS or the AFM. The FSM started with the TPS which checked out.

 

I moved onto the AFM with the manual on page EF 61. At the ECCS plug, the resistance was about 215. So fail. I started the component check. The four pins on my AFM are labeled 34, 33, 32, and 25 with 34 off on its own. The FSM shows to use 33 and 26. The picture shows 26 in the same position as 32.

 

This is a bit confusing as to if I am using the correct pins. Can somebody clear this up? I checked the resistance using the labeled pins on the AFM pretending that 32=26. The resistance was 217. It seems to me that the AFM is faulty. Would I be wrong to assume so? When I got this motor with all the parts, the cover on the AFM was so loose it would fall off which leads me to believe somebody was trying to modify it. That's why I assumed it was the AFM.

 

As always, thanks for any and all assistance!  

[cgsheen]

Just about everyone reporting doing that test seems to get something in the low-to-mid 200's rather than the 420 or so the FSM says it should have...  If the cover has been taken off the AFM and the glue blobs on the screws inside are broken, then someone has probably tried to "adjust" the AFM.  ROOKIE MISTAKE!  The AFM is the LAST thing you should ever screw with - and you should never screw with it until you know everything there is to know about Bosch L-Jetronic and their AFM design.  So, basically it shouldn't be touched and it's the first thing people seem to go to, fiddle with, and totally screw up.  There is a way to "re-calibrate" the spring setting (after-a-fashion), bit you've got a lot of thread searching and reading to do.

 

Just so you know - proper first steps:

- download the FSM(s)

(use the '82 FSM if the ECCS troubleshooting steps in the '81 turbo supplement aren't clear to you - same, same - just no dropping resistors on the injectors and your CAS is external, not in the dizzy)

- There can't be any vacuum leaks or split intake boots on an L28ET

- Ignore the parts in the FSM about using an ECCS analyzer, go to the section that tells you how to test ALL the ECCS components with an electrical meter and a pot of hot water.

- TEST every component except the AFM using the information in the FSM.

- Repair or replace every component that doesn't test properly (including wiring and electrical connectors - clean every connector - then clean it again)

- Know that if you've changed, deleted, or ignored any of the ECCS components listed in the FSM and shown in the various diagrams, the engine is not going to run like the FSM says it should run.

- Once you know everything else is perfect, and it still runs like a pig, search for the AFM calibration thread (way old but fairly famous) OR find an unmolested AFM (I'm giggling to myself as I type that - it's like finding a Unicorn...), OR do the smart thing and ditch the stock ECCS and get a good engine management system...  If I had all the hours back that I spent fiddling with the stock ECU, harness, and parts - I could build another Z.

[alexx933]

Thanks for the input cg. I bought a megasquirt and spark set up that I haven't begun building yet. But i need a compatible CAS. I was just thinking that this could be somewhat simple while I build and plan the MS&S. The amount of time You've helped me is greatly appreciated. Your advice to run a different EMS instead of messing with the stock system is a good idea. I guess my time can be better focused on something more long term.