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1993 Vr-4, Fresh rebuild. This issue was present before i cracked a piston 2 years ago. The car will not rev past 5200rpm, when it hits that mark it bucks and "knocks" but not actual knock according to my sensor.(sensor is good). It throws a code 53, as per 3sx engine scan tool. Occasionally it will run like it is misfiring, but i can shut off individual injectors and it isnt an actual misfire just runs really rough, but most of the time it purrs and is smooth until about 5k. Every thread i have read says that it can be a bad ECU, PTU, coil packs, plugs, wires, or a boost leak. In trying to solve this issue i have since replaced every piece of the ignition system besides the noise condensor. This includes a Chrome ECU upgrade and swapped over to OBII. I have fixed all boostleaks with the car, using the 3sx plate they sell. Now i have attempted to get a tune and the dyno operator COULD get the car past 5200rpm but it was backfiring and jerking hard to push past that.(Painful to watch) Now just before then i had trailored the car to NC and had the guys at 3SX go over the entire car, they told me i just needed a tune after all the work they did. Clearly that wasnt the case. One thread i found mentioned a link between the Tachometer not working properly and it pulling a Code 53. My tach has been off the entire time ive owned the car, been told i need a rebuild of the guage. the piggyback i used to have in the car would show me the correct RPM Just like my Current 3sx Engine scan tool does. So my next step was to pull the dash and try to rebuild that rpm guage, to me that is a last ditch time consuming option. Any advice is helpful- Jason
 

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Pulling that cluster,and then the gauge is nothing compared to what you've done....
To me, it sounds like a fuel issue..
Original pump and and wiring?

Just my .02

Bob.
 

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Discussion Starter #3
Pulling that cluster,and then the gauge is nothing compared to what you've done....
To me, it sounds like a fuel issue..
Original pump and and wiring?

Just my .02

Bob.
i have not pulled the fuel pump to tell if it is OEM or not.(i don't think it is hot wired or upgraded) I did however put new 370cc injectors in with a new fuel filter. The car had 550's and was very rich (going off of AFR). and i am trying to go closer to stock all around anyways. Thank you for the idea Bob, ill pull apart the fuel pump next chance i get.
 

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So can you rev past 5000/5200 at idle? Or light throttle?
 

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So can you rev past 5000/5200 at idle? Or light throttle?
I am a little confused by your question, do you mean like can i rev past 5000/5200 in neutral? If so that is a great question i have not thought of that as the car wont build boost in neutral. Also it is under all normal in gear driving conditions, whether it is light throttle or WOT.
 

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Yes, i was trying to determine if the issue was isolated to when you are under a high load/boost situation as that could be fuel cut. But if it does it under say, light throttle gently accelerating in 1st gear, that's probably not the issue. But i would still try revving in neutral...

How much boost are you trying to run?
 

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Alright i understand now. It occurs under no boost situation, light throttle in 1st,2nd, etc. I had the car on wastegate pressure (6psi) when i tried to get it tuned. Currently i have the HKS electronic boost controller (set up by 3SX) set to 10 psi with a kickback to 5psi if i hit 12psi. Runs smooth and pulls nicely (good AFR's) if i stay under 5ish K. Thank you for the replies jrhorne !
 

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Yes, i was trying to determine if the issue was isolated to when you are under a high load/boost situation as that could be fuel cut. But if it does it under say, light throttle gently accelerating in 1st gear, that's probably not the issue. But i would still try revving in neutral...

How much boost are you trying to run?
Alright i understand now. It occurs under no boost situation, light throttle in 1st,2nd, etc. I had the car on wastegate pressure (6psi) when i tried to get it tuned. Currently i have the HKS electronic boost controller (set up by 3SX) set to 10 psi with a kickback to 5psi if i hit 12psi. Runs smooth and pulls nicely (good AFR's) if i stay under 5ish K. Thank you for the replies jrhorne !
 

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Do you have a wideband? Do you have datalogging? What do AFRs look like when you pass 5k? There has to be odd behavior in some parameters... AFRs, timing, etc.
 

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Do you have a wideband? Do you have datalogging? What do AFRs look like when you pass 5k? There has to be odd behavior in some parameters... AFRs, timing, etc.
Yes i do have a wideband, i do not have a datalogger. I need to get the thing from 3SX that taps into the chrome ecu still. Im not very well versed on dataloggers, The AFR's when going into boost go from like 14.5ish down to 10.5ish-12 under boost.(The AFR's dont alter from what they were before hitting 5ish K) Like i said it needs another tune, i gutted the cats and fixed some major boost leaks since the last tune. The tuner mentioned that he was changing the timing trying to get past the issue, he described it as "an alternative redline" and that "it acts like it is knocking but it isnt" he didnt know why it was happening. The actual timing belt is spot on with the cams. Thank you again jrhorne!
 

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Wait the car had 550s before you did all those mods, specifically the Chromed ECU? If so what was controlling that fuel? If the 550s were after the Chromed, did you go back into the settings when you changed to 370s? The "backfiring and jerking" certainly sounds like fuel cut....
 

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Yes i do have a wideband, i do not have a datalogger. I need to get the thing from 3SX that taps into the chrome ecu still. Im not very well versed on dataloggers, The AFR's when going into boost go from like 14.5ish down to 10.5ish-12 under boost.(The AFR's dont alter from what they were before hitting 5ish K) Like i said it needs another tune, i gutted the cats and fixed some major boost leaks since the last tune. The tuner mentioned that he was changing the timing trying to get past the issue, he described it as "an alternative redline" and that "it acts like it is knocking but it isnt" he didnt know why it was happening. The actual timing belt is spot on with the cams. Thank you again jrhorne!
It does sound like it could indeed be a tune issue if it does it even in neutral... can you get a basemap for a stock car if you are just running 370 injectors? A tuner connected to the ECU just revving the car in neutral should be able to figure out what is going on when it has the issue at 5k; they shouldnt even need to do a pull on the dyno if its doing it under all conditions.
 
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Have you verified the cam timing? We recently had this same exact problem and the car was 3 teeth off at the crank.

Sent from my SM-G975U1 using Tapatalk
 

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Definitely a fuel issue came to my mind.
A fuel issue doesnt seem to fit because the issue occurs even revving in neutral, and the issue does not occur under boost below 5k rpm. If it was a fuel supply issue and the car wasnt revving over 5k in neutral i don't think there's any way it could be running OK under boost below 5k.

The tune aspect still seems suspicious to me... I am also not sure about the tach concerns.
 

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I know we are just spit-balling here until the OP comes back but, if he didn't change his injectors in the tune when he went from 550s to 370s, that could conceivably cause this. 370s have roughly 67% of the fuel capacity that the 550s do. Assuming everything else was the same for the tune, his ECU would be ramping up the injector duty cycle like crazy to try and make up for the difference until it is physically over running the smaller injectors. That could explain why it.

I just checked ChromedECU's site and it states this about closed loop fuel trims:

The long term fuel trims are a way for the ECU to remember how much correction is needed to keep that perfect AFR again. Problem is, it only has so much range. About +/-12.5% in the ROM.
Granted I'm getting out of my league here as I don't know shit about tuning, but if I'm reading it right the Chromed ECU can only adjust up to 12.5% of the injector pulse width based on target AFR vs actual AFR in closed loop. So in OP's situation would it not make sense that he is "running out of injector" under light throttle/low boost due to the ECU thinking the injectors are injecting X amount of fuel, but are instead getting .67(X), attempting to adjust and running into that +/-12.5% hard limitation of the ECU?

There also appears to be a fuel cut safety limit based on engine load, but I don't see how that would ever kick in when revving in neutral.

I'm also interested in how OP is able to disable individual injectors without the ability to also data log. I know the LCDBC offers a feature to disable injectors on the fly, but obviously a LCDBC allows for logging with a $5 cable( although an LCDBC would also explain how OP is sure knock isn't getting reported). Perhaps OP is using a fancier OBD2 scanner? If so those usually also allow real-time viewing of data while the car is running which might be a viable option to see injector duty cycle, ECU reported RPM versus the tach, etc.
 

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If it were the injector setting issue in the ECU, he would be running quite lean. I don't think he would have the 'normal' AFRs he said under boost with the injectors set to 550 but running 370. Basically, if the injector settings were off that much, it would be obvious everywhere not just 5k+.

Does chrome ECU add the additional capability to do closed loop fueling under high load situations using a wideband? Assuming it does not, he would be in open loop under WOT/high boost (so fuel trims are irrelevant), and he would be very lean everywhere not just at 5k+.

Also, you are talking about LTFTs; what about STFTs? That's what matters for the more real-time fueling corrections. I honestly don't know the STFT limitations on our ECUs (i am way more familiar with BMW ECUs at this point lol), but in my logs they show more than +/- 12.5%. Interesting discussion, but i don't think its related to his problem.

Agree about fuel cut, that's why the first question i asked was if it happens revving in neutral.

He said above that he is missing the cable for the chrome ECU. A key next step is to get real-time monitoring and data logging capabilities - we need to know what is happening at 5k+. Its strange that he said AFRs dont do anything odd when he hits the issue... It's also strange the tuner couldnt figure this out...
 

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If it were the injector setting issue in the ECU, he would be running quite lean. I don't think he would have the 'normal' AFRs he said under boost with the injectors set to 550 but running 370. Basically, if the injector settings were off that much, it would be obvious everywhere not just 5k+.

Does chrome ECU add the additional capability to do closed loop fueling under high load situations using a wideband? Assuming it does not, he would be in open loop under WOT/high boost (so fuel trims are irrelevant), and he would be very lean everywhere not just at 5k+.

Also, you are talking about LTFTs; what about STFTs? That's what matters for the more real-time fueling corrections. I honestly don't know the STFT limitations on our ECUs (i am way more familiar with BMW ECUs at this point lol), but in my logs they show more than +/- 12.5%. Interesting discussion, but i don't think its related to his problem.

Agree about fuel cut, that's why the first question i asked was if it happens revving in neutral.

He said above that he is missing the cable for the chrome ECU. A key next step is to get real-time monitoring and data logging capabilities - we need to know what is happening at 5k+. Its strange that he said AFRs dont do anything odd when he hits the issue... It's also strange the tuner couldnt figure this out...
Well the car has had a decent amount of work done to it before i got it, i was trying not to post a build sheet due to its complexity and how it has changed since my ownership (3 years). Also the issue of not being able to rev over 5k since i bought it and AFTER the rebuild. I replaced a ton of parts during that because some of them were shotty and the builder lost a good amount of them. Anyways here it goes. Got the car on a trade and it ran horribly, so i unplugged the MAF and it ran OKAY still not going over 5k rpm and tach not working. Drove it like that until it blew up. (I was saving for a tune and didn't hardly know anything). It had a big FMIC intercooler, 13g turbos, full exhaust, vent to atmosphere BOV, 550cc injectors, badly wired in SAFC-II piggyback, "rebuilt" ecu, HKS air intake, Stock MAF, Turbo Timer half wired in, some melted wires.(guy told me he overcharged the battery, frying the ecu.. etc). It also already had A boost pillar with aftermarket boost guage and wideband O2 sensor.

Currently 3SX has gone through basically the entire wiring harness solving most of my issues. The list of things i did to the car is as follows, EGR block off plates and delete, EVAP delete, (basically all the emissions related stuff is gone), vacuum reduction. Like i mentioned earlier i replaced alot of factory things like water/ oil pump, tensioners, coil packs, ptu, plugs, spark plug wires, re-manufactured MAF, there is more im sure thats new just cant remember right now. The chrome ecu and boost controller were installed by 3sx, they also went over and redid most of the deletes/ reductions. They went through the wiring harness and replaced most of it ($$). My goal is to have about 14psi boost, i rebuilt the engine to factory specifications. (wish i wouldve just done the 3.5 stroker at this point). So the i got the tune done after 3SX worked on the car and it had the 370cc injectors in at the time. Since i got that tune i have gutted the cats and fixed 2 major boost leaks and some small ones. Now it needs another tune just because of those things. Also it was weird because they did a remote tune from New York (I got it tuned in St. Louis area) so it was hard to talk to the tuner as i didnt really know what to ask or anything like that.

I did get to work on the car some over the past couple days, i revved the car in nuetral watching the '3/S touchscreen OBD2 Scan Tool'. (That is how i monitor my knock and can shut off individual injectors etc, it does a ton of stuff. worth the purchase). Anyways the AFRs were fluctuating at idle etc (needs a tune), ill try to post the video shortly so you guys can understand what im talking about better. I tried to remove the fuel pump, It has been removed in the past %100 (Not by me). It looks like an aftermarket wire harness on it.(will post a picture). but i couldnt get it out because the main fuel line is corroded. Im letting some PB blaster penetrate At the moment. Thank you guys again and sorry for not posting in a couple days, and for the long thread but i want to paint a full picture. I appreciate you guys!
 
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