Problems with V6 swapped MR2

Car was at the 2019 challenge and the 2020 challenge but has been sitting a lot since then. Trying to get back up and running, so giving full story to date and see if anyone has some other suggestions of were to go next.

First had some problems with leaking fuel lines cheap ebay  stuff, so I replaced that with better lines, would start and run about 2 or 3 seconds and shut off. Car would keep running on starting fluid so I thought it was a fuel delivery problem.

Next cleaned the fuel filter and took a part the regulator and cleaned it out. We installed a return fuel system in the car for the swap. Everything looked good 41 psi fuel pressure, same problem, starts and runs a few seconds then stops. Then, after about 6 start attempts  we get no fuel pressure.

Take the pump out and test, intermittent at best, so replace fuel pump. Put system back together now we have solid fuel pressure, and same problem. Figured it could be a MAF so unplugged the MAF and the car runs in limp mode.

OK problem solved bad MAF, order new one, install same problem. Can runs unplugged and as soon as you plug in the MAF car dies. If you leave MAF plugged in car runs for a couple of seconds and quits. Today I checked the 12 V ignition source at the MAF connector, ground, the 5 volt reference, and the continuity of the MAF sensor wire to the ecu, all good.

To replace the ecu I would have to find the correct one and then have it programmed for the Key to bypass the security lock out, so I really don't want to do all that to find out that is not the problem. Any ideas?

Thanks in advance

Is it possible that you have a different bad sensor that the ECU is happily ignoring when the MAF is unplugged and it's running some sort of limp mode base map?

Is the fuel pressure still good when it dies?  Some systems run the pump for a few seconds on startup to build pressure.  If you aren't getting pressure/voltage when it does run it would die quickly.

In reply to ¯\_(ツ)_/¯ :

No codes thrown on ecu with maf plugged in so not sure. Scrolling through torque app live feed all of the sensors seem to have reasonable outputs.

In reply to porschenut :

Fuel pressure is still the same when it dies.

I was just looking at a different MR2 wiring diagram. 

If yours is the same, there is a dual coil relay that turns on the pump. One coil fires with the starter and the other with a signal from the maf. 

If the relay that is signaled by the maf isn't firing or isn't connected, then the car will start on fuel pressure but die shortly after.

Actually, thinking about it more, might be good to check that the injectors keep firing too, though we assume they do not and that is why the engine dies. Noid light maybe?

What do you have for a PCV system?  Runs fine as long as the MAF is unplugged sounds like you have a false air situation.

In reply to Pete. (l33t FS) :

pvc system is stock toyota camry. Engine vacumn running without MAF is 22 in.

This circuit opening relay is the one im talking about. The red wires give the FP power with the starter, but after the starter isnt engaged anymore, the relay needs to get signal from elsewhere (in this case ECU, the G-R wire) to keep the fuel pump running.  On earlier cars that other signal came from the MAF, but it appears to come from the ECU in the 2nd gen cars. 

Luckily it looks like you can test for fuel pump voltage easily at the 1 pin of the 'check' connector. I guess you can probably just hotwire the fuel pump too to test if "fuel pump losing voltage" is actually the issue. If fuel pressure stays good even when the car dies as you say then it is unlikely the real issue. 

http://freewiringdiagram.blogspot.com/2018/01/1993-toyota-mr2-wiring-diagram.html

In reply to Robbie (Forum Supporter) :

Thanks Robbie. I have been too busy to get a chance to work on the car, should be able to get to it this weekend and I will update here. My first thought is to just bypass everything and hook a power supply to the fuel pump and see if things change.

So to eliminate fuel pump issues, I connected a 12 volt power supply to the fuel pump. This kept it running independent of the cars electrical system. The result was same problem, car runs with maf unplugged, but only runs for a couple seconds with it plugged in.

Running out of ideas.

Could it be building a ton of vacuum in the fuel tank? Any difference if the cap is cracked open?

Are there any tears, gaps, or other possible sources of un-metered air in the intake boot between air filter, MAF, and throttle body? I noticed something very similar when I got my 2GR V6 swap running last week. Fires right up with MAF unplugged. If I plug in the MAF, I have to have the entire intake hooked up. This was a problem for me because I was modifying the intake at that time, so it would start, run, then die after a couple seconds. I fixed it by taping up the gaps between MAF and TB. 

In reply to maschinenbau :

From the MAF to the TB I am running the stock Camry intake, and a bit longer intake pipe to the MAF. Now the tubing is more than 20 years old so there may be some cracks I did not see. I will see if I can replace that piece of hose and see if it changes anything. Thanks for the insight.

I am bringing my 27 Ford up to the Cars and Caffeine on Sunday so hopefully Ill have some more news by then.

In reply to GameboyRMH :

No and the fuel pressure is steady in all cases. I can start the car and have it running with MAF unplugged and as soon as I plug in MAF the car dies.

In reply to Fladiver64 (Forum Supporter) :

That SCREAMS false air.  The engine runs fine with the MAF unplugged, which rules out mechanical issues, rules out ignition, rules out the fuel system.  With the MAF unplugged it is running off of assumptions based on throttle position and engine speed, and a MAP if it has one. 

If it will not run with the MAF plugged in, then 99% of the time it is because air is getting to the engine that is not being measured by the MAF.  Torn intake boot, PCV system open to atmosphere (such as if you have the oil filler cap off).  Installing the MAF backwards can also do it because it will not be reading correctly.

One thing you can try to rule out any electrical issues is to backprobe the 5 volt reference at any of the sensors that share it with the MAF and see if that 5v disappears when you plug it in.  I have seen sensors kill the 5v bus before, but it is usually the EGR valve on a GM V6.

Ok so started over today.

Repairs made:

Replaced old air inlets with new silicone hoses, both ahead and behind the MAF

Found the EGR pipe was missing two nuts causing a exhaust leak.

Looks like EGR sensor was unplugged, re installed

Took all injectors out and cleaned, replaced O rings.

Replaced fuel rail washers as we developed a leak re assembling.

Test Preformed

1. Run on starting fluid to eliminate spark issues. Runs without fuel pump running as long as we meter in starting fluid

2. Test fuel system, fuel pimp run on external 12 V power supply, getting 46 psi on gauge and return fuel to tank. Checked and both fuel rails are getting fuel.

3. Installed noid light, Blinks during cranking, 

4. Vacuum gauge installed when running without MAF, 23 in idle

5 Ran engine at 3K rpm with noid light installed, as soon as MAF plugged in Noid stops flashing and engine dies. 

6. Preformed same test as above but plugged into MAF that was no installed in the intake, same result

7. Checked the 12V signal that is shared be several sensors and MAF plugged in or not all of them measure 12 v. It does not look like the 5V sensors are shared with any other sensors.

8. If MAF plugged in and engine is started, runs for about 2 or 3 second, then dies. No codes shown on the OBDII. IF MAF unplugged I get MAF error and IAT Error but car will run poorly.

I think I am down to an ecu problem but I would sure like to prove that before going to that expense, I would have to get an ECU and them have the VATS reprogrammed.

I have a friend with a snap on OBDII scanner that is coming over Thursday next week, so maybe that will tell us something else. I have a feeling this is something very simple but right now it is escaping me.

You have 2 mafs right?  And they both don't work?

I'd check that all wires that go from maf to ECU in fact all go from maf to ECU. Maybe one is shorted somewhere?

May also be worthwhile to check that the fuel injectors still have power when engine dies, it's possible it is a fuse or relay or wiring problem cutting power to them rather than the ECU telling them not to fire.

Startup is most likely controlled by open-loop presets, then after a few seconds, it transitions to feedback (sensor)-based operation. I'd be takin a hard look at the MAF harness. The principle of operation requires keeping a precision heater element at a set temperature as it's exposed to the ingested airstream. That heater element often uses a dedicated power line, sometimes switched by all manner of complexities and fed via a tangled Gordian knot of squiggles on the wiring diagram. One obscure missing fuse can kill it.

Absolutely sure the MAF isn't installed backwards airflow-wise?

Stupid question of the day, was it running with this set up as is a couple years ago?  Or is the swap something new? If the same, any changes at all between then and now?

If so, go back to that and see if it runs, if not, well, the mystery continues. 

The fact that it runs in limp mode makes me agree that it will be something stupid and simple, finding it is always the challenge. 

I also think that running in limp mode means it's probably not anything to do with the ECU.

In reply to Robbie (Forum Supporter) :

Yes both act the same way. I even tried pluggin int he spare not installed and same issue.

Checked 5 pins at maf, 12 v source is correct, 5 v reference from ECU is there, Ground is good, and continuity measured between maf sensor wire and ecu good.

The 12V is common to 3 other sensors and I checked the 12v source at the other sensors with the maf plugged in and it was still good.

In reply to maschinenbau :

Will not install the other direction, I tried, the tabs on the MAF keep it the correct orintation.