Code 24 and won't fire - any suggestions?

[GrimJack]

Driving home today I passed a Supra going the other way on the freeway, pulled over with the hood up. So of course, I take the next exit, turn around and go see if I can help.

Fellow has an 88 targa turbo, red, and it won't start. When I get there it will still fire, but won't catch enough to start. I dig around in my trash until I find a staple, bend it to fit the diag block with a set of pliers I carry, and pull the codes, he has a code 24. No other codes.

I unplug his AFM on the idea that it should start and idle even without it, and it still won't start.

Checked the usual connectors, AFM, CPS, ISC, TPS... no luck there.

By the time we give up, it won't fire at all... just cranks when you turn the key.

I didn't have a full set of tools handy in the car, so I can't check for spark on the spot... but it was firing initially, so I'm thinking he's likely got spark.

No fuel? How could I check that on the side of the road? I can snag some tools and run back later if it might help.

Any other ideas?

 

[rakkasan]

Did you ask him when the last time the fuel filter was changed? If you find that he has spark, my bet will be no fuel is making it to the motor.

 

[Godspeed]

24 is air intake tempreture does that mean it got to hot?

 

[shaeff]

for shits and giggles, i'd check the ground wires at the back of the intake manifold with the eyelit connectors on the ends of them. jump the fuel pump using +B and FP, and try starting it. (that'll run the fuel pump)

other than that, it should start even with the AFM disconnected, and idle...

just throwin' out some ideas here.

-shaeff

 

[jetjock]

What shaeff said. If you can hear the pump running the odds are good you've got pressure but you can always crack the CSI line to be sure. Or squeeze the main return line. Even with a bad air temp sensor it should still start so the code must be incidental. Check for injection by listening with screwstick. Also, there is nothing like a can of starting fluid to resolve the spark/fuel question. Spark? Pull one wire and check it the old fashioned way against the block..

I realize it doesn't help you any but I've got a quick disconnect on my fuel rail that makes snapping in the gage I carry a piece of cake. Btw Grim, way to ask a question...I see you've been taking your own advice

shaeff: If were only gonna stick to fuel I don't see how the grounds you mentioned could be involved as the ecu sinks the injectors.

evil: I'm taking your word code 24 is air temp, if so that'd mean the THA signal from the AFM was either open or out of range.

 

[Godspeed]

code 24 is the intake air temp signal for 87 and later models according to the haynes toyota supra repair handbook page 6-4. so no need to take my advice simply giving you guys what the book says.lol

 

[jetjock]

Haynes? Ugh . Not questioning you my man, just that I don't have the book handy and you asked what an air temp code meant. Induction air temp is measured by a thermistor on the AFM and that code would indicate it was out of range when last sampled by the ecu. So in some ways yes, the ecu would "think" intake air was too hot but in that case it'd go ahead and set a default value of 65 F (I think, could be 68 F) in order to maintain drivability.

It then goes and sets code 24. A key thing to remember is Grim only got the code when he jumpered the block so that means it wasn't a "hard" fault. Could even be there from him unplugging the AFM at the wrong time.

 

[Godspeed]

true i see your point. as far as haynes its the only manual i can find for the supe. chiltons made one but no longer prints them so its all i have.

 

[IJ.]

24 Intake air Temp Sensor Signal
Diagnosis
Open or short circuit in intake air temp sensor signal (THA).
Trouble Area
Intake air temp sensor circuit
Intake air temp sensor
ECU

 

[Joel W.]

my thought as i was driving back home, was first, +1 to grim if i could for going out of his way to help a supra stranger out, and second, i have seen on other cars, not a supra yet, where the fuel pump works but is not creating enough pressure for the injectors to work properly.. could this cause a lean situation that could trip the code 24??

 

[NJsupraA70]

I would trace the THA wire from the afm connector back. It is pastel green in color. . I think a quick way to test that the THA wire is good is to: Connect THA and E2 together on the afm connector and Code 24 should go away.

 

[jetjock]

Joel: No, that wouldn't cause a code 24. All the thermistor in the AFM does is measure intake air temp so the TCCS can correct for density in the A/F trim.

NJsupra: E2 is the ecu's digital ground. I believe shorting THA to it would cause a code 24, not remove it, as that would put the sensor out of range. The sensor should be ohmed and the value compared to the temp chart in the manual. The wiring should them be checked.

Again, if the code only shows up when the block is shorted it's not a hard fault and can be cleared until the next time. Still, your method is a valid way to check the wiring once the code is cleared

 

[Joel W.]

jetJock, I didnt really think it would except maybe if it could run so lean it overheated and raised engine compartment temps?? but it was a long shot

edited for sprellering.

 

[jetjock]

jetrock? Lol, have you and the "boost get's you laid" guy been talking to each other? R and J aren't anywhere near each other on my keyboard

Remember, any time the TCCS detects a sensor failure (within it's capabilities) it does more than set a code and light the MIL. It also substitutes a fixed value so the EFI system doesn't go too bonkers.

And you're absolutely right: Kudos to Grim for his kindness. Sometimes I can't see past the tech stuff to what's really important

 

[Joel W.]

i fixed it for ya, my bad. its late.. lol

after dealing with the SM name thread i swear i almost mispelled soup, >> suop.

 

[ATS_Scott]

Did you reset the ECU to see if the code 24 returned? I think Jet jock is right it's just a leftover code. There is something else wrong.

I'd check the fuel pump for voltage when cranking and that the circuit opening relay is staying energized after cranking.

 

[LamaRossa]

Grim

happens to me all the time

try wiggling the connector for cam position sensor that connector is fuckked all the time CPS i made a new one never had the problem again

ciao

lamarossa

 

[jetjock]

I'd check the fuel pump for voltage when cranking and that the circuit opening relay is staying energized after cranking.

That's a good call. After all, jumpering the diag block to check the fuel pump does nothing to test the COR. As far as connectors, I've said it before: every connector for the TCCS should be treated every 30K miles or so with a good anti-corrosion product like ACF-50 or Corrosion X. Just cycling them will help but they can't be ignored. In 140,000 miles I've never had a single connector problem of any kind.

 

[shaeff]

jetjock, the only reason i said to check those grounds at the back of the head, is i believe they're the injector grounds (read that several times) and without them making a solid connection, the injectors wont open regardless of whether there's fuel in there or not, as they would not receive the signal.

that was just a guess anyway.

-shaeff

 

[jetjock]

Sir shaeff, what you've read is inaccurate. Normally I wouldn't correct this kind of stuff but you come across as one of the more knowledgable here so I'd thought you'd like to know.

The grounded side of the injector wiring runs from the injectors directly to the ecu. The ecu turns the injectors on and off by switching them to ground. That ground is supplied by the main ecu ground at ecu pins E01 and E02. There is no injector grounding supplied by any other point. Hope that clears things up. See the thread "Injector Driver" for more info.