The Top DSM Community on the Web

For 1990-1999 Mitsubishi Eclipse, Eagle Talon, Plymouth Laser, and Galant VR-4 Owners. Log in to remove most ads.

Please Support Rix Racing
Please Support ExtremePSI

420A STFT -100 LTFT -100 ECT -40 P0300-304

This site may earn a commission from merchant
affiliate links, including eBay, Amazon, and others.

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

tj_tatum

Probationary Member
2
0
Feb 8, 2017
allen, Texas
97 420A with no mods; resetting the ECU to get all the monitors ready for inspection. the car will randomly get the p0300 - 304 pending and eventually lights the CEL. The scanner i have only gives freeze frame data. no matter if im driving or sitting still the fuel trims show -100, engine coolant temp -40(its 70 degrees in Texas today); rpm and speed show 0. I have cleaned ground connections and checked ECU connections. could this be an ECU on the way to going out? note the car runs fine and doesn't hesitate or anything before this happens
 
You must be logged in to view this image or video.
Picked up a new temp sensor as the plastic housing broke while measuring the resistance. The sensor came with a new connector. Checked the wires back to the ECU and checked voltage to the plug; all was well. I reset the ecu and went to run the drive cycles. While traveling at 40mph, the P0300-305 came up pending. The freeze frame data shows the fuel trims at -100 and the Ect at -40; also strange was the engine RPM and speed where at 0. Any thoughts?
 
ok ive seen this before. blown sensor ground trace inside your ecu

take the cover off and you will see a thin silver trace on the circuit board that is burnt up. if you are lucky you can repair it. Sometimes other components are damaged on the board so you may want to have ecmtuning take a look.


edit:
Shit I didnt notice you were a 420a. This might still apply.

-40 on ect still says ECU grounds problem, maybe internal, maybe external.
 
Last edited:
so this started happening after u reset the ecu? maybe a sensor wire is flipping out, awhile back I found out multiple sensors share the same power wire, for instance the cam, crank, and vehicle speed sensor share the same power wire so if the wire is messed up it affects all 3 sensors and in turn affects their signals to the computer which needs those signals to run. now a lot of times people have cracked wires in the loom right above the EGR valve tube on the 420a, maybe check those wires out and the circuit for the cam and crank sensor cuz those will throw the P0300 code. also as far as the fuel trims, maybe check the o2 sensor and circuit and and the map sensor on the intake manifold as well as fuel pressure. the joys of the 420a is that its really easy to check the fuel pressure with a tester from orielly's or autozone (I checked mine in the parking lot so they didn't even charge me to rent the tool)
 
I would use another scanner and make sure those readings are correct. Your car should be running pretty bad (if at all) with no rpm signal, -40 ect,and fuel trims all at -40. You may be chasing a ghost. Your misfires could simply be bad coil, wires, plugs, or injectors.
 
I see that this Post is from 2017 and know it’s been 2 years, but was wondering if this was ever resolved?
Because I am having the Exact Same Issue,
97 420a, runs great, no hesitation or sputtering but have a CEL with P0300 & P0301-P0304
 
your ecu is not getting a ground reference for those sensors. This likely is due to a blown sensor ground trace on the ECU PCB. You can probably check by opening up the ECU and looking for burnt up traces. Please let us know if you figure anything out.
 
@rabenne , Thank you.
From the reposnses to this thread I’ll be changing out the ECT first. Then I’ll be pulling out the ECU and open it up
 
Update: changed the ECT (Engine Coolant Temperature Sensor) it has been 24 Hrs and the CEL hasn’t come back on. Will give it another 24 Hrs become I’m completely satisfied.
 
Update:
Update: changed the ECT (Engine Coolant Temperature Sensor) it has been 24 Hrs and the CEL hasn’t come back on. Will give it another 24 Hrs become I’m completely satisfied.
Before I’m completely satisfied*
 
Update: CEL came back on with same codes, decided to take a picture of the Freeze Frame it showed me. Wondering if anyone can help descypher it’s meaning...
 

Attachments

  • DC1A253B-4E42-4229-ABE4-B49D98FCE1CE.jpeg
    DC1A253B-4E42-4229-ABE4-B49D98FCE1CE.jpeg
    1.4 MB · Views: 59
Support Vendors who Support the DSM Community
Boosted Fabrication ECM Tuning ExtremePSI Fuel Injector Clinic Innovation Products Jacks Transmissions JNZ Tuning Kiggly Racing Morrison Fabrications MyMitsubishiStore.com RixRacing RockAuto RTM Racing STM Tuned

Latest posts

Build Thread Updates

Vendor Updates

Latest Classifieds

Back
Top