Hi Guys I’m new to this and also new to the fiero world. I have 1987 with the 2.5 with a stick. The check engine light is on but I can’t get it to flash the any codes an I also cant get my scan tool to hook up as well. The car was sitting for about 8 year. I had to replace the fuel pump. Cause it was bad. I also replace the water temp sender for the ecu because it was bad as well. The car also does not go into high idle. The coolant fan is on all the time as well. If I could get any help. That would be awesome.

Should be able to pop codes with a paperclip, don't need a tool except to read live data (don't know how that works, never done it.) Remember these cars are *old*.

See

https://www.fiero.nl/cgi-bin/main.cgi?ECMCodes
https://www.fierostore.com/.../Default.aspx?Id=347

-- A

So can start/run engine but MIL light on and can't scan ECM?

Can try getting code w/o engine running but if MIL is on w/o running engine then this likely won't work.

ECM have 2 power feeds...
1 run by I-switch and normal fuse. Likely Not your problem.
1 goes to battery to save "Codes" and whatever else. This has 1 connector to reset the ECM and could have problems there or at + "box" under C500

ECM can partly work and be "dead." Often cause by heat generated by ECM can't get rid of.
Scanners need I-key turned On but can scan and get codes ECM w/ and w/o engine running.
May need replacement ECM, Save The PROM in old unit for use w/ new one. PROM is under removable case. Carefully Pull up whole plastic holding the PROM.

ECM should scan even setting MIL light on but many "scanners" have setup to work.
Exactly what scanner are you using?
Scanning w/ PC have more issues/problems and some hardware and/or software won't w/ 1227748 ECM for 87-92 L4.
WinALDL won't work. Need other software.
If using old serial scan "cables..." many PC won't work w/ them and many Serial2USB because many can't handle non-standard serial data GM uses. Plus Many "cables" not wired for data out on ALDL M

See my Cave, Fuse Links notes, ECM Heat and others.

------------------
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave

[This message has been edited by theogre (edited 01-24-2021).]

Hi I’m using a snap on scan tool. It’s an mc2000 the red brick. How can I test the ecu. Or make sure it’s that before I just buy one. Also we’re can I get one? Thank you guys for your help

Hey. Guys. I was wondering with the problems I’m having would the proms be bad in the ecu. I can get one at the local advance store. It’s about 110 bucks. Any help would be great

Did you try jumping out the ecu with a paper clip? Those old computers were far from standardized and wouldn't expect a scan tool to work.

quote Originally posted by skywurz: Did you try jumping out the ecu with a paper clip? Those old computers were far from standardized and wouldn't expect a scan tool to work.

Isn't that what I said?

-- A

quote Originally posted by dremu: Isn't that what I said? -- A

Why yes it is! Which I was asking if he had tried that yet

quote Originally posted by skywurz: Did you try jumping out the ecu with a paper clip? Those old computers were far from standardized and wouldn't expect a scan tool to work.

Fieros work great with similar vintage scan tools, I use the Snap-On MT2500 (big red brick) with my 84, I also have a video of a Fiero GT being diagnosed with the more primitive OTC Monitor 2000:



OP may have bad wiring on his diagnostic connector, that would be the first thing to rule out.

Is the check engine light always on? Like always with the ignition, always with engine running - no visual sign whatsoever that something is controlling this light, like it was turned on manually by a switch? Might be a short inside or close to the ECM causing this pin to go high no matter what. Might be a short in the ALDL connector itself. The fan is not controlled by the ECU. If you put yout heater to vent mode or off does the fan shut down? Sounds like wiring issues to me here. If the engine is running then the ECU is likely all good.

quote Originally posted by skywurz: Those old computers were far from standardized and wouldn't expect a scan tool to work.

Another w/o a clue claiming whatever...
Old ECM are not "Standard" like OBD2 vehicles but Scan tools are used by every maker w/ "OBD1" vehicles and while slow to read often the data you get can save many hours of time to find whatever is wrong. In case of any DIS engine, is Only thing to tell you info you need as Often Doesn't even have timing marks on crank pulley/balancer.

Common example to all cars: Reading Ω at ECT and others is often useless because of crap wiring or iffy ECM. Scan the ECM tells you coolant temp in seconds and tell you sensor lying or bad for bad sensor or crap wires and don't need to dig out ECM to Ω the wires.
Also Crap GM wire/plugs to ECT is why you can't get old ECT sensor. To replace you must upgrade for MetricPack plug and use new sensor. 87 started w/ new ECT plug and most parts outlets not just GM dealers Stopped carrying old unit. For many years many ECT sensor had right plug in the box and directions to use it.

quote Originally posted by RWDPLZ: Fieros work great with similar vintage scan tools, ... OP may have bad wiring on his diagnostic connector, that would be the first thing to rule out.

Or a iffy scan tool/cable. Snap-on can break. Run tool on other old GM vehicle ideally w/ data stream on ALDL M. You can see E or M because only 1 is wired in ALDL port.

Many ALDL cables and sockets in cars have problems. More so w/ sockets in cars because fools push large "wires" into them to flash code on the dash and wreck the ALDL "pins." Scanners for GM cars must get good connection w/ ALDL A B & E OR M at minimum depending on Engine and Year of car.
If ALDL A B or both is wreck then expect problems scanning... As One is the ground and other sees "Resistor value" (1 to several real resistors or emulation of same) to trip ECM data stream to E/M pin or to read DTC on scanner screen.
Pull Console to get at ALDL back and pull out "pins" to inspect/fix ends. Think release pins same method w/ "tool" in See my Cave, Defect & Connection notes

[This message has been edited by theogre (edited 01-27-2021).]

Hey guy. Just wanted to give an up date the ecu. Was bad. Put a new one in. The car runs. Great. Only problem is the tach is reading way high. Is there any fix for this. I seen on others post that. There is a guy that fixes them

Many Fiero ECM die from heat...
See my Cave, ECM Heat to get more air on the ECM case.

Tach is another issue and unrelated.