Mitsubishi 3000GT & Dodge Stealth Forum banner
1 - 20 of 107 Posts

·
Premium Member
Joined
·
3,311 Posts
Discussion Starter · #1 ·
This is going to be a long description. I have been dealing with a very frustrating intermittent electrical problem on my VR4. I start the car and I will hear the MFI relay click and the car shuts off. Sometimes it is 4-5 seconds after starting, sometimes it can be a few minutes. It seems like when its a cold start it occurs more frequently.

Background:

94 vr4 with 66k miles. I've been running AEM v2 since 2011, self tuned. The issue started last fall after making a TON of changes. In early summer I pulled the motor and sent the trans, diff an my dr750s off to be re-built. While things were away I worked on the motor: Kevlar timing belt, solid tensioner, new Valve Stem Seals, BC 264 Cams, BC adjustable cam gears (degree'd properly), new oil pump, Fluidampr, new clutch, new plugs and a Rvenge Coil on Plug kit. I removed my HKS DLI and my Blitz DSBC and installed an AEM boost solenoid. I also redid some of my intercooler piping to go with a Synapse bov vs the Tial because I was having surge problems with my dr750s. And I updated the firmware in AEM v2 to v25. I boost leak tested everything.

My first start was fine. I was able to top off fluids and let it warm up for 20 minutes before shutting it off. The next day I went to start it again and was having the issue. I thought I had tracked down the issue a few different times, only to be wrong. I believe I had just messed with the car long enough that the motor was warm and the issue wasn't occurring.

First I uninstalled my turbo timer thinking that was it. Next day problem persisted. Then I rolled back firmware on ECU thinking that was it. I actually took the car for a 15 minute drive afterwards without issue. Next day problem persisted. I've since put firmware back on v25. V25 does have engine safety features but I've confirmed they are all disabled.

Then I did the Fuel Pump Relay bypass by the stock fuse box. With my old vr4 I had a shutoff problem too and bypassing the relay solved it. That didn't help. I also tested the MFI relay on the workbench (tested fine). Just to be certain I swapped it out with a spare I had, and then another spare. Same problem... I heard my IAC chattering one day after it died so I replaced that with the newer plastic style, same problem. I tested all the +12v inputs and ground inputs at the ECU with multimeter. I cleaned my battery terminals. I sent my ECU into AEM where they tested and confirmed it was working fine. Because of what I described to them, they did replace the main relay in the board out of precaution.

I got the ECU back and the problem still exists:( So this is when I started looking at the wiring diagrams surrounding the MFI Relay.




This is what I drew up. I also pulled the cover off the MFI relay and watched it as it shut off. Its the Fuel Pump side of the relay that kicks off. So to me this means it is either power going to the relay coil or the ground on the other side (AEM). In AEM I used the internal logger to monitor the Main Relay and Fuel Pump relay (LS11) to make sure it wasn't calling for them to shut off. It wasn't. I also jumped pin 7 of the MFI relay to power to confirm that car didn't shut off. So this leads me to believe the problem is somewhere in the area I highlighted. Somewhere between pin 7 of the MFI relay and the ignition I've got an intermittent issue.




I looked back at the diagram to find the path the wire takes. From the ignition harness it goes to back of fuse box, through the fuse, out the front of the box, to a drivers side dash connector, out a passenger side dash connector, and then to the MFI relay connector. I started adding a jumper wire from the MFI relay to different spots of the harness to track down where he bad spot was. I had found that plugged into the drivers dash connector it would still stall. But when plugged into the connector going into the back of the fuse box I had 3 successful cold starts where it warmed up to operating temperature without issue.







So I thought for sure it was the fuse box. I took it apart and cleaned everything with electrical cleaner (didn't really seem dirty). I soaked all the fuse crimps (the things the fuses snap into) in alcohol and pinched them together with pliers to make sure they had a tight connection. Red shows how power comes into the fuse and green shows where it comes out. This didn't help:/






I have a spare wire harness for a 94 vr4 so I replaced the little 12" section of wiring that comes out of the front of the fuse and goes to the drivers dash connector. That didn't help. I also tried 2 different spare fuse boxes I had. No dice. I also depinned the wire in every connector and made sure it looked fine (it did). I cleaned with electrical cleaner anyways. For the female spade ends I also pinched with pliers so they would fit as tight as possible. The female spade at the MFI relay has some solder on it. I touched it with my soldering iron and added some fresh solder.



So last night I took apart my ignition assembly and cleaned the contact points. No help. I had a spare steering column out of a 52k mile vr4. I stole the ignition assembly off of that and it didn't help.






I'm going to try and repeat the jumper wire test. I've tested continuity, I've tried monitoring voltage to see if I can see a drop with my multimeter but I think it happens so fast that I can't detect it. I tried hooking a small fog light up to the wire to see if it ever dims or shuts off when the car dies but it doesn't. Maybe it's flashing so fast that I can't see it. I'm wondering if maybe I'm not looking at something correctly or there is something else I should be doing? I read online some multi-meters have a min/max setting to catch quick changes. Mine doesn't. I'm thinking about buying one though.

Thanks - Charlie
 

·
Premium Member
Joined
·
5,946 Posts
A new ignition switch is around $20, the one you have in the picture shows some wear. On my car, if the battery voltage fell below 12.3 volts with the worn ignition switch, it wouldn't even fire up the starter relay. Replaced the ignition switch, and I could start the car even if the battery was down to 12.0 volts, I didn't test any lower as to not damage my battery. Anyhow, that's my two bits.
 

·
Premium Member
Joined
·
7,101 Posts
You've done an excellent job of tracing out the powerflow of the system, locating all the components, and determining how it all works. What does strike me through is the testing methods seem to be pretty intrusive, and shy on data gathered. Seems to me you'd get a much better picture much faster of what's going on simply employing a test lamp and volt meter. Confirm with actual voltage readings that the ECU is providing a strong ground path for the control side of the relay, and measure the voltage at the power side. If getting a drop, check different sections of the circuit to hone in on the high resistance. Using those methods will take out the guesswork and confirm without doubt you've found your problem, and confirm your fix.
 

·
Senior **i.e. OLD** Member
Joined
·
15,404 Posts
That guy ^^^^ knows his way around our cars "attic".
Make that THOSE two guys...

I know throwing parts at a car is NOT the right way to fix it, but his suggestion makes sense and his reputation alone is worth the $20.
And I think you can handle what Larry has suggested...

Good Luck Charlie (and Happy New Year [since I haven't spoken with you lately])

Bob.
 

·
Registered
93 NA ATX 3000gt DOHC
Joined
·
2,986 Posts
After reading your description of extensive troubleshooting and about what you’ve tried, I find some unusual inconsistencies concerning the circuit involved. This makes me wonder if you’ve confused some of the results or if an intermittent problem might be in play as well.

If power at pin 7 of MFI is momentarily interrupted and all else correct, the relay would simply blip open and closed so fast that I question if the blip in pressure from pump would be long enough to stall engine.

On the other hand if ground from pin 5 (White/red wire) was lost relay would open and stay that way until ground was restored. I know you think it’s a power delivery problem but I’m not sure especially since you couldn’t detect voltage drop with multi-meter when problem occurred.

Might try running a temporary ground wire from pin 5 (White/red wire) to any good chassis ground point to see if that corrects issue, if it does then might need to troubleshoot why ECU is dropping that ground.
 

·
Premium Member
Joined
·
3,311 Posts
Discussion Starter · #6 ·
Thanks for the replies... Any kind of advice is appreciated. I've been dealing with this for 3 months. Its winter now in Vermont so I have about 3 more months to figure it out.

I will order 2 OEM ignition switches Monday just because. Will be nice to rule that out 100% and to have a spare.

I did test power at the ECU pins 12 and 25. I also tested continuity to ground from pins 91, 13, and 26 all the way back to the negative post on the battery. I had measured voltage at pin 7. It would be 14.x volts and then when the car died it would drop to 12.x volts. I also cleaned the ground that bolts to the firewall near the battery.

I didn't test anything with pin 5 because when I had jumped pin 7 to 12v it didn't die on me. I have about 5 warmups (2 from the relay jumped directly to the harness on the ignition and 3 jumped from the connector on back of fuse box) where it didn't die. I just went and pulled pin 5 from the connector though and I ran a ground wire to the relay connector. AEM would not behave. My fuel pump would prime forever (instead of just 1 second) and it didn't want to stay running at all. I wonder if AEM somehow reads feedback from that pin?

I made a video of my multimeter monitoring pin 5:


And here is a video of it monitoring pin 7. I watched it in slow motion and I did see it dip to 11.27v but I can't tell if that is after car shuts off or before. Thinking about it maybe I should repeat the video with just turning the key off:

 

·
Registered
93 NA ATX 3000gt DOHC
Joined
·
2,986 Posts
The monitoring of pin 5 appears to show a problem to me. With key on showing 11.86v is normal but when key is turned to start and after engine running that voltage should drop to ~ 3v or so and stay there until key is turned off, or until ECU drops ground which should cause it to return to about the 12v range. It appears when engine starts yours looks like it’s going to ~ 128v, which makes no sense to me. I don’t know anything about AEM units, maybe someone that knows those units can offer an explanation.

Pin 7 video looks normal, at least what I’d expect to see.
 

·
Senior **i.e. OLD** Member
Joined
·
15,404 Posts
Where the hell is @Steve '93ES ?

You have the best helpers...

You got this...

Bob.
 

·
Premium Member
Joined
·
7,101 Posts
The monitoring of pin 5 appears to show a problem to me. With key on showing 11.86v is normal but when key is turned to start and after engine running that voltage should drop to ~ 3v or so and stay there until key is turned off, or until ECU drops ground which should cause it to return to about the 12v range. It appears when engine starts yours looks like it’s going to ~ 128v, which makes no sense to me. I don’t know anything about AEM units, maybe someone that knows those units can offer an explanation.

Pin 7 video looks normal, at least what I’d expect to see.
I've had a hard time telling what's going on on my screen, but it looked to me like it was switching to MV scale.
 

·
Registered
93 NA ATX 3000gt DOHC
Joined
·
2,986 Posts
I've had a hard time telling what's going on on my screen, but it looked to me like it was switching to MV scale.
That could be, I see something small show up in lower right corner of meter but can’t tell what it is. But if so that would be 0.128v which seems unusual low, but I’m not sure what to expect from a AEM.
 

·
Banned
Joined
·
220 Posts
Chances are it's your AEM ECU that's faulty

As has already been said, you should be using a voltmeter, waste of time swapping anything until you know where the fault is, that's what the meter is for.
The AEM uses a switched earth to operate the MFI relay, that's where you should start. Use clipleads so that the meter is permanently attached so you can monitor the various wires one at a time.
 

·
Curmudgeon
Joined
·
5,693 Posts
I'm here. It takes me a minute to catch my breath after carrying Don's tool box... ;)
I'm a bit confused though. Like Don I know nothing about the AEM, but if jumping MFI pin 7 to power fixes the problem (even temporally) why are we looking at pin 5?
Grounding pin 5 BTW will force the fuel pump on any time the key is on (pump would prime forever (instead of just 1 second) I'm not sure why it wouldn't run like that unless the AEM does monitor that pin...

If this were a stock system I would be wondering if an intermittent crank sensor was causing the ECU to drop the MFI signal..
You say the AEM logs that though? Is crank signal something we can rule out?

I cant quite see the buttons on your meter but if you can select a range instead of letting it "auto range" you might clean up some of those funny readings..
 

·
SDSU Alumnus
Joined
·
3,877 Posts
Not to ask the obvious, but what are your main relay input and output settings in AEM? If the ignition switch is suspect, then you can perform a "test" by trial and temporarily raise your "stop engine" duration in the options menu (with the rest adjusted accordingly...)

-sent from my Galaxy Note 9
 

·
Registered
93 NA ATX 3000gt DOHC
Joined
·
2,986 Posts
I'm here. It takes me a minute to catch my breath after carrying Don's tool box...
You need to start carrying my brain; it’s a lot lighter these days.:D

Like Don I know nothing about the AEM, but if jumping MFI pin 7 to power fixes the problem (even temporally) why are we looking at pin 5?
I mentioned that because he indicted relay was opening without any significant drop seen on multi-meter (assuming taken at pin 7 of relay) and I knew that couldn’t cause relay to open, so I questioned dropping of the ground.

If this were a stock system I would be wondering if an intermittent crank sensor was causing the ECU to drop the MFI signal..
Since you already brought up crank sensor while I was typing, I’ll show it below any way.

Since pin 7 and assuming pin 5 test are in order, it might be something else causing engine to die, which would cause the ECU to drop fuel pump side of relay after few seconds. Just for giggles, take a look at wire coming from crank sensor up front of timing belt cover, to make sure the accessory belt hasn’t cut into it.
 

·
Premium Member
Joined
·
7,101 Posts
I'm a bit confused though. Like Don I know nothing about the AEM, but if jumping MFI pin 7 to power fixes the problem (even temporally) why are we looking at pin 5?
I advised him to get actual voltage data on both mainly because the data we had at that time was anecdotal and did not rule out coincidence.

At this point I see no issue with the readings at the MPFI, and I'm not convinced the relay shutting off isn't a result of the engine shutting off and not a cause.

I have no clue why jumping power to the circuit would fix it if it isn't losing voltage at the relay. Has pin 82 been monitored during the failure event?
 

·
Registered
93 NA ATX 3000gt DOHC
Joined
·
2,986 Posts
@ fastfalcon94 I got to tell you that with the below list you can’t get any better information.

BlackStealth
RealMcCoy
OhioSpyderman
Steve ‘93ES
bboyalan


That’s a hell of a knowledge list of minds about these cars.
 

·
Premium Member
Joined
·
3,311 Posts
Discussion Starter · #18 ·
perform a "test" by trial and temporarily raise your "stop engine" duration in the options menu (with the rest adjusted accordingly...)
Hmm, I haven't messed with that. It's set to 0.5 seconds (what AEM delivers it as) and it's been that way for 10 years. You are saying if I make it higher maybe that will give me some time to see something else happening? Here is a pic.



take a look at wire coming from crank sensor up front of timing belt cover, to make sure the accessory belt hasn’t cut into it.
I'll double check that, but I know the zip tie push pin was in tact. I also went through the factory service tests for the cam and crank sensor before sending my ECU in.


Tomorrow I'll see if there is a way to log the sensor input with AEM. Here is a picture to show why I didn't think it was AEM calling for ECU to turn off. You can see where the RPM drops and the MFI Main Relay and MFI Fuel Relay are still on. I know its the fuel pump relay turning off because I labelled each side of the relay and I can see it physically opening back up.





Its worth noting that if I rev the car to 3-4k rpm this can still happen. When it does the car will act like fuel cut but come back to life as the engine is still spinning fast enough. You can hear the relay click. I put my calibration file and 2 log files in a zip file if anyone wants to take a look. In one of the log files the car shuts off idling. The other I'm trying to hold the rpm steady at 3-4k and it drops.

 

·
SDSU Alumnus
Joined
·
3,877 Posts
Hmm, I haven't messed with that. It's set to 0.5 seconds (what AEM delivers it as) and it's been that way for 10 years. You are saying if I make it higher maybe that will give me some time to see something else happening? Here is a pic.
Yeah, those are the correct, default settings. But yes, if it stayed running longer for whatever increased duration, then that may give more insight especially if it ended up being the ignition switch. Larry had already mentioned Pin #82 for main relay/ignition switch too.

Since cam+crank sensors were also mentioned, you can open the "advanced pickups" tab and log those parameters to rule out any dropped signals (instead of probing the wires with a meter/scope)
 
  • Like
Reactions: white93gt
1 - 20 of 107 Posts
Top