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Discussion Starter · #1 ·
My car sat for about a month, while I was waiting for E-85 to be available locally. Charged up the battery and drove to the Valero for some E-85. Car was running smooth 900-1K with the heater running(haven't used the heater in a long time)

Filled up a full tank of E-85 that pump was running pretty slow to be honest. Cranked up and left the store, did a small pull nothing to crazy.

Went outside city limits did some back country launches and pulls. I noticed two things that happened.

1. After doing pulls and launches my Idle was at 1500-1600 RPM steady RPM
2. I lose power at 5K RPM!!!! The car pulls strong but once I get near 4-5K RPM it's like I hit a Rev limter, it won't go past 5K no matter what, 2nd gear 5K, 3rd gear 5K.
It feels like fuel or spark cut not sure what it is.

I can lay on the petal in 2nd but it won't move past 5k while WOT.

After looking over things I can't figure it out. I did a boost leak test, no leaks.
I adjusted the Throttle arm/screw back down. This seemed to lower my idle back to 950ish rpm. I still have the loss of power at 5K. Not sure what to look at?
 

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SDSU Alumnus
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It definitely sounds like a leak(s) lol

-sent from my Galaxy Note 9
 

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Discussion Starter · #4 ·
hmm, boost leak was my first guess as well. Where/how did you test it?
I'm using the Rob Beck/3SX version. Really the only leak that I can hear is like inside the throttle body or near it...but I had the throttle body rebuild by April, and when I spray soap and water I don't see any bubbles.

I'm stumped on this one. I'm using the stock fuel filter but it's been replaced within the last year.
 

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1500 rpm warm idle could be a world of things. Sometimes its as simple as the dashpot needs adjusted (or removed) try pulling the gas pedal back with your foot, if the idle drops, It's the dash pot or the Throttle body cable is too tight and barely hanging it open, Also Check the BISS Screw, and if 91/92 car, check the Ignition timing and adjust via CAS. Could also be a early sign of a failing FIAV, or lack of coolant in the car causing the FIAV to hang open (since you mentioned running the heater, its probably cold/cooler out then normal currently, which tends to make FIAV failures show up) Kinked Throttle body coolant hose could cause this too.

For loss of power, you Could be experiencing spark blow out, check age of plugs, run NGK Coppers and gap at .025-.028. Often presents itself more as just a missfire, but I've come across it feeling more like hitting rev limiter early....Since you are on E85, Could also be a dying fuel pump, collapsing filter (Cheaper aftermarket inline Fuel Filters tend to be notorious for this), or just insuffienct fuel...

What does your wideband say? what tuning solution are you using? I'm guessing it goes past 5,000rpm fine on low/zero load.. maybe post some logs, Hook up a gauge and monitor your fuel pressure underload. That's a super easy way to rule it out as a being a fueling issue. I've had a collapsing fuel filter cause a Stealth RT/TT I had years ago to both feel and sound like it was hitting Rev Limiter

Back to the tuning solution, it is possible its just fuel cut depending on how and what the car is running on for engine mangement... Those tend to be more rev limiter like in nature...Sometimes even more so like hitting a brickwall type rev limiter.
 

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Discussion Starter · #6 ·
1500 rpm warm idle could be a world of things. Sometimes its as simple as the dashpot needs adjusted (or removed) try pulling the gas pedal back with your foot, if the idle drops, It's the dash pot or the Throttle body cable is too tight and barely hanging it open, Also Check the BISS Screw, and if 91/92 car, check the Ignition timing and adjust via CAS. Could also be a early sign of a failing FIAV, or lack of coolant in the car causing the FIAV to hang open (since you mentioned running the heater, its probably cold/cooler out then normal currently, which tends to make FIAV failures show up) Kinked Throttle body coolant hose could cause this too.

For loss of power, you Could be experiencing spark blow out, check age of plugs, run NGK Coppers and gap at .025-.028. Often presents itself more as just a missfire, but I've come across it feeling more like hitting rev limiter early....Since you are on E85, Could also be a dying fuel pump, collapsing filter (Cheaper aftermarket inline Fuel Filters tend to be notorious for this), or just insuffienct fuel...

What does your wideband say? what tuning solution are you using? I'm guessing it goes past 5,000rpm fine on low/zero load.. maybe post some logs, Hook up a gauge and monitor your fuel pressure underload. That's a super easy way to rule it out as a being a fueling issue. I've had a collapsing fuel filter cause a Stealth RT/TT I had years ago to both feel and sound like it was hitting Rev Limiter

Back to the tuning solution, it is possible its just fuel cut depending on how and what the car is running on for engine mangement... Those tend to be more rev limiter like in nature...Sometimes even more so like hitting a brickwall type rev limiter.
Great info! When the idle was 1500 rpm warm I did pull back on the gas pedal but it didn't fix the idle. After doing a boost leak test the only solution was to adjust the Dashpot screw to a lower idle.

I was wanting to remove the FIAV and clean it but never did. MIght take it off and clean it but when the RPM was turning on the AC dropped the RPM. That tells me here might a vacuum leak but for the life of me I can't hear a major leak.

My wideband is reading normally 14.5 at idle. I'm running NGK Coppers, NGK wires, everyone gapped when installed the 13g turbos. I want to say the plugs and wires only have about 1,000 miles on them. The Fuel pump and filter all replace at the same times as the plugs and wires. Walbro 450 and stock fuel filter.

As far as tuning I'm running Chrome V2 and Jester's maf.

I'm wanting to say it's a vacuum leak but I pressure tested it. The vaccuum pressure at idle was 19 ish on my PLX wideband. When I unplugged the vaccuum line to the Blow Off Valve it did raise the idle a few more RPM from 1500.

I could try to clean the FIAV, should I raise the idle back to 1,500 RPM using the dashpot, then try to clean the FIAV. To be honest I need to check the coolant level, maybe it went low after using the heater. That would solve the idle issue but the loss of power at 5K RPM unless it's both connected.
 

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Discussion Starter · #7 · (Edited)
Here is a recent video. 1st gear and 2nd gear pull at Wide Open Throttle. My ECS computer is rebuilt but shocks are the problem. I should unplug the ECS computer.

It just won't go past 5K you can see and hear what it does. Is that fuel or spark cut? Any help would be much appreciated




Edit someone said it was my Speedometor/Tach. I'm charging up the laptop to see the different my RPM needle is at vs Evoscan. Will try to update tomorrow. Thanks for the quick response. Any other things to look for would be helpful.
 

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TIRED OF WAITING
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I would have to agree, the video shows it as your speedo is probably close. 5speed trans do roughly 35 and 75 mph in first and second gear. Be cautious of bouncing off the rev limiter till you get your tach sorted out.

Clay
 

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Lovbyts
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Ill tell you what finally fixed my 1500 rpm idle when war after MANY years of trouble shooting. Multiple vac check, smoke test, changing gaskets and most every small and large part always thinking I found it but didnt.
My last tuneup I decided to also take off my intake manifold and have the threaded holes drilled out and new E-Z Locks/Keenserts put in because the helicoils I put in many years ago were pulling out. I also had my manifold and plenum surfaced because I noticed my manifold was pretty uneven.

Slapped it back together and first think I had to do is start cranking my idel up because it was around 300 rpm for the first time since I can remember.

What did I replace over the last year+ coils, plugs several times, wires, gaskets, TPS, ICA, throttle body rebuild. ECU/ECS rebuilt, BOV, various vacuum lines, one way valves, Turbo intake hoses and a few dozen other things. All seemed to help a little for a day or two but the idle was still always high. Now I can easily drop my idle via bis screw until it dies where before always around 1500.
 

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Discussion Starter · #10 ·
The issue might be the speedometer/bad capacitors or resistors...unless it's something else like PTU? I'm leaning towards the speedometer cluster. Just like to hear everyone's thoughts? The only change I made-I unplugged the ECS computer in the trunk. Still no change on RPM. This tells me the caps might be bad in the cluster or it's a different issue.

Here is the current Evoscan Datalog. I made a quick video too. The RPM/Tach is off! I was hitting 7.4K RPM when my needle was showing 5K very very dangerous!

YouTube Video at cold idle and I rev the engine to 3K rpm(shows on EvoScan in video) and the Tach showed 2K.


EvoScan File
 

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That's absolutely a tach cap issue. Mine was doing the same thing. Very dangerous with the low RPM reading!

It's mandatory maintenance in 1G cars at this point.

65 cents worth of caps from my spare Mouser stash fixed it immediately.

 

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Discussion Starter · #12 ·
That's absolutely a tach cap issue. Mine was doing the same thing. Very dangerous with the low RPM reading!

It's mandatory maintenance in 1G cars at this point.

65 cents worth of caps from my spare Mouser stash fixed it immediately.

View attachment 298445 View attachment 298446
Sweet! I'm relieved but also concerned. I only did 4 pulls but going into 7K+ isn't good. When running the track I really on shift at 6K max.

Thanks for the pictures Lawdogg! This will be a project I can tackle. My dad was in the Navy for electronics repair/micro soldering and did that for many years. We still have a local electronics store that stocks, all the caps ect. I really didn't see a how-to-video, this might be a good time to make a video. I'll keep everyone updated.
 

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93 NA ATX 3000gt DOHC
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I really didn't see a how-to-video, this might be a good time to make a video. I'll keep everyone updated.
If you make video, may I suggest you do not remove the needle and face, because that requires you to deal with recalibrating tach after capacitors replacement. Both capacitors can be replaced without removing needle and face, I know because that’s how I did mine. Below is link to cluster removal if you haven’t done it before, only thing I'll add to it is pull the trip reset pin out before removing the cluster, because it takes a hard pull to get it to release from speedo unit.
 

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Discussion Starter · #14 ·
If you make video, may I suggest you do not remove the needle and face, because that requires you to deal with recalibrating tach after capacitors replacement. Both capacitors can be replaced without removing needle and face, I know because that’s how I did mine. Below is link to cluster removal if you haven’t done it before, only thing I'll add to it is pull the trip reset pin out before removing the cluster, because it takes a hard pull to get it to release from speedo unit.
I have a few questions if you don't mind. I picked up 2 50V 10uf capacitor. Couldn't get the 35V but voltage doesn't matter much, but it must be over 16V capacitor.

How do you get to the circuit board inside the cluster? I know there are a ton of silver screws in the back of the unit. I'm not sure if I have to remove the face of the cluster to get to the board or if I only remove the back portion. Thanks in advance.
 

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93 NA ATX 3000gt DOHC
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I have a few questions if you don't mind. I picked up 2 50V 10uf capacitor. Couldn't get the 35V but voltage doesn't matter much, but it must be over 16V capacitor.

How do you get to the circuit board inside the cluster? I know there are a ton of silver screws in the back of the unit. I'm not sure if I have to remove the face of the cluster to get to the board or if I only remove the back portion. Thanks in advance.
Those 2 capacitors will work fine, the voltage is only required to be same or higher than originals. The originals was 10 uf and 25V, not sure where the 16v thing came from.

If you have cluster out and trip reset pin out, you have to remove the clear and black covers from the back white plastic housing by releasing one clip at a time until all are free then cover just lifts off. Take that slow and easy at each plastic clips just enough to slightly free one clip a little then move to next alway around, as those old clips are easy to break. After both clear and black plastic are removed from the back white housing, there will be 3 screws coming into tach board from back printed circuit board (of white housing, remove those 3 screws and entire tach assembly can be removed from white plastic housing. Those 3 screws also act as power delivery, ground and signal connection from rear printed circuit board to tach circuit board. That will allow access to bottom of tach board which is side capacitors are soldered too. Just be careful capacitors are soldered in with same polarity as old ones (note negative indicating stripe on side of capacitors).
 

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Discussion Starter · #16 ·
Already finished up with the repair. I was able to grab 2 50V 10uf capacitors and replaced them. I found that only 1 of them was leaking...but might as well replace the other. Plz don't hate me too much. I wasn't able to get the repair on "video" but I was able to snap many pictures, which I thought would be WAY better then a video. I made another video doing some pulls with the Tach/RPM fixed. My idle is still a little high but nothing too crazy. She still pulls hard but main thing is seeing the correct and accurate RPM reading.

Thanks again for everyones help, I would of been replacing a bunch of parts for nothing without doing some testing.

I'm going to make a How-To-Write up if anyone needs help doing this repair. The Mileage/Speedometer side I took apart but it's more difficult to repair then the Tach side.

Tach Fixed video
 

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I found that only 1 of them was leaking...but might as well replace the other.
Better be glad you replaced both, neither of mine had leaked and looked brand new. I don’t know where the thought that a capacitor had to leak to be bad came from, it only visually confirms a capacitor needs replacing, it might actually still be working and the non-leaking one could be the dead one.
 

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Discussion Starter · #18 ·
Better be glad you replaced both, neither of mine had leaked and looked brand new. I don’t know where the thought that a capacitor had to leak to be bad came from, it only visually confirms a capacitor needs replacing, it might actually still be working and the non-leaking one could be the dead one.
Yup very hard to tell. I was able to use my rms meter and seen both up in the very high megaohmz. Like you said, it's best to replace them both.

Here is the How-To-Repair thread in the How-to section of the forums, if anyone has a similar issue you can see the step by step thread here.

 

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TIRED OF WAITING
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Nailed the 1-2 shift. Sure is nice to finally see what you need to see in able to drive it properly.

Clay
 

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Discussion Starter · #20 ·
Nailed the 1-2 shift. Sure is nice to finally see what you need to see in able to drive it properly.

Clay
Amen to that! I'm glad this was caught early because it would have cost me an engine!
 
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