Popps then Shuts Off again.

gkomo · Jul 31, 2025

Code 21 may be fixed with a new ECT sensor. Front of the passenger side lower intake manifold.

I have a code 44 and hopefully my new 'unclogged' air crossover tube clears that for me. Both my existing tube and head holes were completely clogged with carbon build up on my passenger side. But if you found a giant hole in the tubing that could be it too. I'm not done with my current project so i haven't been able to start her up and rerun codes yet.

robw13 · Aug 9, 2025

Still not running good.
KOEO = Codes 18
KOER = Cyl 8 21, 44, 94

Won't go anywhere further and will eventually die. Is the reader saying there's a an issue with cylinder 8? Maybe it's misfiring?

Parts changed since died on highway:
IAC, Smog Pump Hose, PCV, Vacuum Lines, Upper Intake Gasket, Valve Cover Gaskets, Dizzy Duralast Gold, Coolant Temp Sensor, Fuel Filter. Do have a New pump if needed.

Noobz347 · Aug 9, 2025

The code 18 needs to be addressed.

KOEO (Key On Engine Off)

Code 18 – Loss of IDM signal / SPOUT circuit fault / loss of tach input to EEC

Common causes: bad TFI module, faulty ignition coil, wiring issues between the distributor and EEC, or a failing distributor pickup (PIP sensor).
- Since it’s KOEO, it points to an ignition circuit fault the computer detects without the engine running. This means that you should be able to troubleshoot it whether it's a connector, wire, etc...

KOER (Key On Engine Running)

Cylinder 8 – Cylinder balance test indicates Cylinder #8 is weak or misfiring

- Could be spark, injector, compression, or vacuum leak at #8.

Code 21 – Engine coolant temperature (ECT) out of self-test range

- Usually means ECT sensor is reading too cold or too hot during self-test. On KOER, this can also happen if the engine isn’t fully warmed up before testing.

Code 44 – Thermactor Air Injection system inoperative (right bank)

Code 94 – Thermactor Air Injection system inoperative (left bank)

- These come as a pair when the AIR pump/diverter valve isn’t sending air to the exhaust during the test.
- Could be due to missing/removed smog equipment, a bad diverter valve, vacuum leaks to the valve, or a dead smog pump.

Tackle Code 18 first – ignition issues can cause false balance test fails and even skew KOER results. Start by checking SPOUT connector, coil resistance, and distributor pickup signal.

Once ignition is solid, retest – see if cylinder #8 still flags. If so, do a compression test and swap plug/wire/injector to isolate.

Code 21 – warm the engine fully before KOER. If it still trips, test the ECT sensor with a multimeter at the correct temp.

Codes 44/94 – if the smog pump is gone or bypassed, they’ll always show. If you need to keep them clear, the system has to be restored or electronically tricked.

Noobz347 · Aug 9, 2025

Code 18 Diagnostic Steps

Check SPOUT circuit continuity

The SPOUT (SPark OUT) signal goes from the EEC to the TFI to control timing advance.
If it’s open, the EEC can’t advance timing and sets Code 18.

Locate SPOUT connector – little gray jumper near the distributor harness.
With ignition OFF, unplug SPOUT jumper.
Multimeter set to Ohms, probe the two pins in the SPOUT harness (vehicle side, not jumper)
One pin goes to EEC pin #36, the other to TFI module.
You should have less than 5 ohms resistance.
- If open/infinite, check wiring from EEC to TFI.

Check IDM signal to the EEC

The IDM (Ignition Diagnostic Monitor) comes from the coil negative through the TFI and feeds tach signal to the EEC.

Key OFF.
Find coil negative terminal (–) and EEC pin #4.
Check resistance between coil negative and EEC pin #4.
- Expect under 5 ohms.
- If open, wiring fault between TFI/coil and EEC.

Test ignition coil primary & secondary

A weak coil can cause the EEC to lose the IDM signal at high RPM or load.

Key OFF, disconnect coil.
Primary: Measure across coil + and – terminals.
- Expect 0.3–1.0 ohm.
Secondary: Measure from coil + to coil tower (where plug wire connects).
- Expect 8k–12k ohms.
If out of spec, replace coil.

Test PIP (Profile Ignition Pickup) sensor output

The PIP tells the TFI when to trigger spark — if this drops out, the EEC sees a loss of IDM.

Leave SPOUT installed.
Key ON, engine cranking.
Backprobe PIP wire (TFI pin #1, usually purple/orange) to ground.
Set multimeter to AC volts (low range).
You should see 0.6–1.5V AC pulsing while cranking.

- No signal = bad PIP or distributor.

TFI module test

The TFI is a common Code 18 culprit.

If coil & PIP test OK but Code 18 remains, swap in a known-good TFI.

- You can also heat the suspect TFI with a heat gun (lightly) to see if it fails hot — common on gray-housing modules.

robw13 · Aug 9, 2025

Cool beans, I really appreciate the help, will get to testing.

robw13 · Aug 9, 2025

On IDM to EEC check, where is pin #4? I know coil to tower is in spec. Infinite on the spout pins.

robw13 · Aug 12, 2025

Looks like the Air Temp Sensor was toast. I've got it to idle on its own now.

AeroCoupe · Aug 12, 2025

An you never got a Code 64?

robw13 · Aug 12, 2025

Yep, no code 64. Crazy

AeroCoupe · Aug 12, 2025

You need to send the ECU to The ECU Excahange and get them to go through it. With all the codes you have got then they have gone away, then get some back, and not getting codes you should get just points to the fact that the ECU is 30+ years old and there are components in it that are aging out.

robw13 · Aug 12, 2025

Are they the best/only place to get the ECU checked/fixed? Could getting one off ebay be a bad idea?

gkomo · Aug 12, 2025

So many success stories from members here. I'm sure they aren't the only shop in town who does this work, but at least you know they are reputable from all of us who have used them.

robw13 · Aug 12, 2025

Ok, I'll pull the ecu and look to see which one it is.

Noobz347 · Aug 12, 2025

You can find rebuilt or remanufactured units on Ebay but maaaaaaaaaaaaaan... That seller better have a few hundred sales and 98+ % feedback with other than [generic] comments.

robw13 · Aug 12, 2025

True, I usually don't buy anything unless their ratings are high. Looking at the prices I'd be better off sending it to be checked.

robw13 · Aug 12, 2025

Went and checked codes again for curiosity,
KOEO - NO 18
KOER - 44/94
KOER Balance - 90

Still has a little sputter while ideling but stays running decent. No dying or jumping.
Do have to lower idle and recheck timing. Probly do a idle reset and how it does. If no change then probly send ecu off. Gonna be a pill to get out though.

gkomo · Aug 12, 2025

Have you checked your air crossover tube from the smog pump to the back of the heads? It may be clogged with carbon buildup not allowing any air to flow.

Not very fun to remove and replace, but a new tube fixed my code 44 (passenger side was completely clogged)

robw13 · Aug 12, 2025

Where can you get a new tube? I'm sure mine is clogged

gkomo · Aug 12, 2025

I believe i got mine from LMR.com

Not like super cheap, for what it is... could remove yours and try cleaning it out. I wanted to go for easiest route to fix which is why i bought a new tube.

AeroCoupe · Aug 12, 2025

If you are not checked for emissions I would just pull all that stuff off, put the block offs on the back of the heads and move on down the road. You can get high flow cats that do not need the air pump if need be or there ends up being too much of a gas smell.

Here is my take on any ECU on eBay, are you going to trust the seller that says its been rebuilt and it 100% good to go? I would not especially with anything electronic.

Popps then Shuts Off again.

gkomo

now i can hopefully expect to receive the shaft

robw13

Noobz347

Stangnet Facilities Maint Tech... Er... Janitor

Noobz347

Stangnet Facilities Maint Tech... Er... Janitor

Code 18 Diagnostic Steps

Check SPOUT circuit continuity

Check IDM signal to the EEC

Test ignition coil primary & secondary

TFI module test

robw13

robw13

robw13

Attachments

AeroCoupe

lube between the nut and the face. I know my lubes

robw13

AeroCoupe

lube between the nut and the face. I know my lubes

robw13

gkomo

now i can hopefully expect to receive the shaft

robw13

Noobz347

Stangnet Facilities Maint Tech... Er... Janitor

robw13

robw13

gkomo

now i can hopefully expect to receive the shaft

robw13

gkomo

now i can hopefully expect to receive the shaft

AeroCoupe

lube between the nut and the face. I know my lubes

Similar threads

Popps then Shuts Off again.

now i can hopefully expect to receive the shaft

Stangnet Facilities Maint Tech... Er... Janitor

Stangnet Facilities Maint Tech... Er... Janitor

Code 18 Diagnostic Steps​

Check SPOUT circuit continuity​

Check IDM signal to the EEC​

Test ignition coil primary & secondary​

TFI module test​

Attachments

lube between the nut and the face. I know my lubes

lube between the nut and the face. I know my lubes

now i can hopefully expect to receive the shaft

Stangnet Facilities Maint Tech... Er... Janitor

now i can hopefully expect to receive the shaft

now i can hopefully expect to receive the shaft

lube between the nut and the face. I know my lubes

Similar threads

Privacy & Transparency

Privacy & Transparency

Code 18 Diagnostic Steps

Check SPOUT circuit continuity

Check IDM signal to the EEC

Test ignition coil primary & secondary

TFI module test