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Discussion Starter #1
Alright, I've had a few posts here and there on multiple threads relating to this so thought I should finally create a separate thread to contain it all in one...

Any help/insight will be greatly appreciated! (side note: this forum has been great, and I've really appreciated all of the shared knowledge on here)

Here's the quick background of my issue and where things are currently at:

Bought a '93 VR4 in summer 2018 after looking out for the exact one I wanted for yearsss:D

Since I drove it home summer 2018, I've had intermittent hesitation issues... I drove it from Iowa to Manitoba so it was 'good' but would occasionally hesitate or buck under WOT. If I drove smoothly without too much acceleration it was fine at the time.
I had to get the car saftied back in Canada.. the issue on that front was getting the horn to work... That issue was finally solved (separate thread for that if anyone is interested: Horn issue - searched/troubleshot/stuck! ), and I needed daytime running lights to pass (another separte thread: Daytime Running Lights - the EASY (free) mod to pass inspection! ) otherwise the car passed for the rest with flying colours.

Fast forward to last summer (2019) and the hesitation was worse but not consistently so more troubleshooting.. fuel injector cleaner seemed to help it but not 100% sure.
Had a rough time driving home one day... everything electrical died on it (had to coast to a stop on the highway, but the engine still ran at idle. After a while it would work again. So basically did this (stopped about 6-8 times along a 1 hour drive), man it was brutal. Now I basically can't drive it reliably.. had some short drives without issue, then if it started happening again it was on and off making for a lonng drive home.
I've also got the OBD1 scan tool from BlackStealth which is awesome so I've got code readouts at least as well so I might be able to narrow it down some more. (I'll add those codes in this thread when I get back to that).
Anyway here is my list I've come up with to look into now that I have some time at home again: (and ideally ASAP in time for getting the car back on the road for this season!)

-fuel injectors, starting with simple injector cleaner (seemed to help somewhat?)
-fuel stabilizer/seafoam etc to help (seemed to help somewhat?)
-fuel filter (bought, not yet installed)
-MAF
-spark plugs/wires (bought, not yet installed)
-ECU capacitors (previous owner told me they were checked and ok, but I see now the ECU doesn't look great even thought the capacitors were replaced) *not blaming him
pictures of the ECU in follwoing post
-TPS
-boost leaks (bought a boost leak kit from 3SX to confirm if there are any issues there)

Hopefully I narrow it down without going through the whole list... but yes that's where I'm at currently!
 

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Your list isnt bad, but the order seems off. I would do:

1. ECU
2. Boost leak (can be done in parallel)
3. Plugs/wires (wait for above unless they are needed anyways).
4. Fuel filter if due anyways
5. Confirm you have good gas. Seafoam isnt going to do anything really.

Also, if you already have the converter, i highly recommend you look into datalogging to start narrowing down your issues. See here:
 
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Discussion Starter #5
Alright, appreciate the input! (Y)
1. working on the ECU now (ordered new capacitors and thinking I may just bring them in with the ECU to a computer or electronics repair shop to see if they can clean up the board... rather than a hack job of soldering on my own since that board already looks a bit rough). Chrome ECU is the backup (which I'd love to get, but not going to be happy if I drop a grand and it turns out not to be the problem..)
2. I'll try to test for a boost leak later this week or weekend
3. Already got new plugs/wires so I'll be installing them at some point soon anyway, even if that's not the cause of the issues
4. like above I ordered one and plan to do it anyway (not very expensive and figured it couldn't hurt to try)
5. I've driven through a couple of tanks of premium gas so that 'shouldn't' be the problem... unless there's rust or something like that IN the tank?

and yes I'll have to start data logging once the snow clears off and I'm out of quarantine/able to take 'er out on some short drives for troubleshooting!
 

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everything electrical died on it (had to coast to a stop on the highway, but the engine still ran at idle. After a while it would work again. So basically did this (stopped about 6-8 times along a 1 hour drive)
Admittedly, I'm not the biggest expert on this but what exactly do you mean by this. If you had a total electrical failure of everything but the engine then I would look at the wiring harness and it's interconnections, most likely at the firewall into the cabin.
 

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Discussion Starter #7
Admittedly, I'm not the biggest expert on this but what exactly do you mean by this. If you had a total electrical failure of everything but the engine then I would look at the wiring harness and it's interconnections, most likely at the firewall into the cabin.
well, the car hesitated/bucked a bit more-so if I stepped on the gas, then at some point died completely (down to idle without stalling out as long as I took my foot off the gas) and the speedo dropped off to 0, radio/lights etc all off.
wouldn't even know what to look for with the wiring harness... I went through a bunch of electrical wiring for my horn troubleshooting so the fuses/relays all seem to be good and connections from everything I saw during that. I'll look at the connections at the firewall again like you said though I guess just to see if anything is loose or shows any signs of corrosion? I got a new/better battery and the alternator works fine.
I haven't driven the car yet this season, so I'm hoping to be able to test some things out again soon once the weather clears.
I also did have thrown codes saved in my Torque app, but apparently lost those when I switched phones :mad: so I'll have to drive and get the same symptoms again to recapture the codes.
 

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Code 41 (IMO) would be consistent with the looks of the solder job on the capacitors in the ECU.
It also could be a failing injector, if your logging program has a way to disable 1 injector at a time, I would try that and listen to the change in sound when each injector is turned off.
No change in sound, or intermittent change may point to that injector.

After seeing your ECU, my guess would be that, but then again, I have no way to prove that...

Bob.
 

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It also could be a connection either @ the ECU or where the harness goes through the firewall. But, Bob is right, I would get another ECU and try that.
 

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IIRC, it is recommended to transfer a bad ECU to another car and observe for the same symptoms. Adversely, transferring a good ECU into a problem car could result in having two paperweights lol especially with something like a bad IAC/ISC, for example. Someone can correct me if I am remembering incorrectly...
 

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Discussion Starter #12
IIRC, it is recommended to transfer a bad ECU to another car and observe for the same symptoms. Adversely, transferring a good ECU into a problem car could result in having two paperweights lol especially with something like a bad IAC/ISC, for example. Someone can correct me if I am remembering incorrectly...
that would be handy if I had the option.. but #1; don't know anyone with a VR4 around me, and honestly #2; don't think I'd feel comfortable putting in something that 'may be messed up' into someone's running car (specifically as important as the brain of the car anyway).. unless that person knew their stuff and really was ok with it
 

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Discussion Starter #13
also, what would the big risk be of putting a good 'working' ECU in for testing? If the ECU is the problem I thought it'd just be because of the damage on the board from previously leaked capacitors. What if anything else has been known to damage the ECU? (aside from flooding/overheating)
 

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also, what would the big risk be of putting a good 'working' ECU in for testing? If the ECU is the problem I thought it'd just be because of the damage on the board from previously leaked capacitors. What if anything else has been known to damage the ECU? (aside from flooding/overheating)
Alan is right. You dont want to put a good ECU into a car with a suspected bad ECU. Problems with other components on the car can fry the ECU. IAC as mentioned is one of them.

You CAN do it, you are just risking the good ECU. Especially since you noted electrical problems, this is not really advisable.
 

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Discussion Starter #15
Alan is right. You dont want to put a good ECU into a car with a suspected bad ECU. Problems with other components on the car can fry the ECU. IAC as mentioned is one of them.

You CAN do it, you are just risking the good ECU. Especially since you noted electrical problems, this is not really advisable.
ok I can see your point.. but where else would you start then with where I'm at? I've ordered new capacitors and once they arrive I will bring in my current ECU along with those to an electronic repair shop first to see if they can clean up the board. Otherwise anything else? (again, I don't have anyone nearby with a VR4 to swap ECUS etc).
I just replaced the fuel filter today (was one thing on my list of potential items causing my issues), and will get around to the spark plugs/wires at some point.
 

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Couple things I would check that don't cost anything or much at all. Use a multimeter to check the coils on the IAC (IIRC, stealth316 webpage has a pretty good writeup on this) and also verify your fuel pump and Ignition Coil Pack are getting proper voltage, especially under load. The Rubber Ducky Racing page (Erik Gross fuel pump rewire) costs little more than a relay, some wires and some time and is good for the overall health of the vehicle.

Also, another note on the ignition coil pack wiring. My '93 VR-4 had intermittent bucking and hesitation issues. Took me over $2,000 of throwing parts at it to figure out that it was only a $5 relay to ensure the coil pack was getting enough voltage under load. I've been deep into this platform for over 20 years and my specialty was 12V wiring as a career for 10 years. Talk about being served a fat slice of humble pie lol... I don't have the thread bookmarked on here for the ignition coil pack rewire but I am sure a few searches would get you there. Best of luck!
 

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Discussion Starter #17
Couple things I would check that don't cost anything or much at all. Use a multimeter to check the coils on the IAC (IIRC, stealth316 webpage has a pretty good writeup on this) and also verify your fuel pump and Ignition Coil Pack are getting proper voltage, especially under load. The Rubber Ducky Racing page (Erik Gross fuel pump rewire) costs little more than a relay, some wires and some time and is good for the overall health of the vehicle.

Also, another note on the ignition coil pack wiring. My '93 VR-4 had intermittent bucking and hesitation issues. Took me over $2,000 of throwing parts at it to figure out that it was only a $5 relay to ensure the coil pack was getting enough voltage under load. I've been deep into this platform for over 20 years and my specialty was 12V wiring as a career for 10 years. Talk about being served a fat slice of humble pie lol... I don't have the thread bookmarked on here for the ignition coil pack rewire but I am sure a few searches would get you there. Best of luck!
Really appreciate this, I've got a few things to check/work on now, but it's great to hear something that solved a similar problem for someone else! and maybe something that won't kill the bank account which is always nice (do that enough already) lol.
I'll look up that thread for sure, but you did a full rewire and ended up tracing it down to a relay eh? I'm not a fan of electrical issues.. nor am I good with them:S. Eventually fixed my horn (running a new wire) but even that was a pain in the a$$ so I was hoping I wouldn't have to dive to far into electrical issues for this.

and side note; why do you say the fuel pump rewire is good for the overall health of the vehicle btw? Just curious, as I've seen a couple of those fuel pump hotwire threads but figured if it's something that's working fine then there was no need to mess with it.. constant voltage better for it I guess?
 

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Really appreciate this, I've got a few things to check/work on now, but it's great to hear something that solved a similar problem for someone else! and maybe something that won't kill the bank account which is always nice (do that enough already) lol.
I'll look up that thread for sure, but you did a full rewire and ended up tracing it down to a relay eh? I'm not a fan of electrical issues.. nor am I good with them:S. Eventually fixed my horn (running a new wire) but even that was a pain in the a$$ so I was hoping I wouldn't have to dive to far into electrical issues for this.

and side note; why do you say the fuel pump rewire is good for the overall health of the vehicle btw? Just curious, as I've seen a couple of those fuel pump hotwire threads but figured if it's something that's working fine then there was no need to mess with it.. constant voltage better for it I guess?
Yeah so the Ignition rewire really wasn't that bad at all. Basically all you are doing is intercepting the power wire that feeds the coil pack and giving it a better 12 V source. You cut the power wire and hook the engine harness side of it into one side of an aftermarket relay (Pins 86 or 85) and the other to a ground. Then you hook the Ignition coil pack side of that power wire to Pin 87 and a proper 12V wire straight from the battery (fused of course) to PIN 30 and voila. I would love to supply pictures but it will be a while as my '93 is being stored at another property at the moment.

As for the fuel pump rewire, I also have a '97 VR-4 that is completely stock and after changing spark plugs one day, thought the engine appeared to be running a bit lean. So I hooked up a multimeter directly to the fuel pump connector and found it was getting like 11 volts. As we know fuel pump output is directly related to voltage supplied, I decided to do the Eric Gross rewire method (this retains the factory resistor for low load) and the voltage increased about 1.5 volts so I was happy with that. I might add a pound or two of boost to this car down the road so I figured it would be smart to address it sooner than later. Here is the link, it is under the "RDR Fuel Pump Rewiring" Rubber Ducky Racing This applies to stock fuel pumps, if you change to a different FP then you would probably want to do the full hotwire and bypass the resistor all together.
 

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Discussion Starter #19
Thanks again AudioPmp23 (I will be trying your suggestions I think next here).

I was just waiting for my ECU to come back first since I had the caps replaced and the board cleaned up hoping that may solve things. Got it today. No luck, same issues. This time I used the code scanner from Blackstealth and logged while I went for a test drive around the block. I could drive 'fine' for a few minutes, got to the gas station, around the block, then basically bucked and lost power (would stay at idle if I let of the gas). After a few minutes of sitting at the side of the road, I could drive 'fine' again, but only for a short period of time so basically just got it back home and that's it.
Below are the codes:
Before I dive into any of the earlier mentioned potential fixes, anyone have a suggestion which way to go first with this?


Current Fault Log
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P0105: Manifold Absolute Pressure/Barometric Pressure Circuit
P0110: Intake Air Temperature Circuit
P0120: Throttle/Pedal Position Sensor/Switch A Circuit

Pending Fault Log
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P0201: Injector Circuit - Cylinder 1
P0202: Injector Circuit - Cylinder 2
P0204: Injector Circuit - Cylinder 4
P0205: Injector Circuit - Cylinder 5
P0206: Injector Circuit - Cylinder 6
 

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The first two are related to MAF i believe (or could be ECU-related, but sounds like you fixed that). If you captured a log, can you upload and send a link? Hopefully you were looking some parameters that would help diagnose or provide insight into potential issue. Specifically, we want to look at the values for the codes - barometric pressure, IAT, and TPS values.

You could also see if you TPS is reading correctly by opening realtime monitoring and even without the car running should be able to check if it goes ~13-100%. If you have a log of when the issue was not and then was present, we should be able to see if any of those 3 values went out of wack.

How does it run if you unplug the MAF?
 
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