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96 geo metro hot soak no spark

dan fitz
11-04-2009, 10:25 PM
i have a 96 geo metro, 4 cylinder with a specific problem of not starting after sitting hot for 5 or 10 minutes, then won't restart until it has cooled for about a half an hour. if i try to start it right after shutting it off, no problem, but after a little while there's nothing but cranking. a passerby cranking the engine with me holding a plug wire close to a ground confirmed there's no spark when this is happening. a friend who turns geo engines into aircraft engines sent me an ignitor module for inside the distributor, a control module (little black squarish unit that is mounted to the firewall in front of the driver), a coil and a new brain. i have replaced everything but the brain to no effect, codes pulled are 400, 420 and 340. anybody had this and figured it out? i'm wondering if there's another sensor affecting the ECU/brain that might have gone bad. car has 200K miles on it, fuel pressure is good, like to keep it running but this one's got me scratching my head. will replace the brain next but i'd like to hear if anyone's dealt with this.

Johnny Mullet
11-04-2009, 10:47 PM
Check Engine Light Guide (http://geometroforum.com/topic/638390/)

P0400 - EGR Flow Malfunction
P0420 - Catalyst System Efficiency Below Threshold
P0340 - CMP Sensor Circuit Malfunction

The P0400 indicates you have clogged EGR passages and maybe the EGR valve is also clogged with carbon. This is typical especially with higher miles. More info on cleaning the ports can be found here..........

The P0420 code indicates the cat converter is either melted down, plugged up, or missing. This is also typical of a high mileage engine and carbon buildup.

Those 2 previous codes are probably not the issue you have, but may need addressed in the future. The P0340 is causing your "No-Spark" issue. This is related to the cam sensor. I am not 100% sure since the 3 cylinder is more my bag, but the CMP is found in the distributor. Call around the parts stores and see if they have a listing for a Camshaft Position Sensor.

dan fitz
11-05-2009, 04:49 PM
thanks johnny; as far as i know the camshaft position sensor function is done by the pickup gizmo inside the distributor, which is one of the things i switched out. i'm thinking that if this were bad the engine wouldn't even start but electronics do get funny when they're hot. almost thinking of replacing the coolant temp sensor just as a what-else-could-it-be-and-it's-only-15 bucks thing. i did replace the brain behind the glovebox yesterday and found myself sitting in the darkened library parking lot with the hood up for a half hour waiting for that magic cool-down temperature where it will start again. any other thoughts out there?

11-05-2009, 06:29 PM
there is also a crank position sensor on the bottom of pan next to bottom pulley. might want to pull the coil wire out of the dist next time and set it next to some metal. the metal part for spark plug is quite a ways up inside boot and may not have enough energy to arc to metal

dan fitz
11-09-2009, 05:30 PM
thanks, i took the crank position sensor out and cleaned it off, put it back in and still the same symptom, my buddy is sending me another one to try and also suggested i try some noalox on the connectors before plugging them back in to be absolutely sure of a good contact. he said his metro had the exact same problem, he threw in the above-mentioned parts and it stopped doing it, he never figured out which part fixed it so he traveled with all those parts as spares in a box, that was 140,000 miles ago and it's never repeated itself.

Johnny Mullet
11-09-2009, 08:46 PM
Make sure the oil pan does not have a gasket on it. The aftermarket gasket is too thick and will make the signal erratic. Do not use a gasket on the oil pan, just use RTV sealant.

dan fitz
11-10-2009, 01:12 PM
thanks JM, i had read about the sensitivity of the CKP sensor to the mere thickness of a compressed cork gasket so i was looking to see if it was just RTV, which it was. i'll post the results of the new CKP sensor after i get it in and test it.

dan fitz
11-16-2009, 06:50 PM
okay, my geo guy sent me a crankshaft position sensor and another cam position sensor, both installed with a little noalox on the contact for extra certainty, neither thing did the trick. thought i had it solved when i put some antiseize paste on the back of the ignition module ( this model it's on the firewall ) as i could see the back of it was exposed aluminum and i thought, hey, it looks like they're trying to get rid of some heat here with the back exposed like that against the steel bracket. tested it once in the driveway and it seemed to work but just now in front of the library where i'm now posting this, it failed to start, same thing as before. any other ideas out there, this is driving me nuts!

11-16-2009, 07:10 PM
did you pull the coil wire and crank it to see if you had spark yet?

dan fitz
11-17-2009, 01:25 PM
i have checked for spark before with no sign of it when exhibiting this problem but i'll give it another shot today. an old post from a couple of years ago mentioned by sdhst28 says he had a defective coil in the throttle body on a '97 with identical problem, not sure what he meant by that as there are several gizmos coming out of the TB. his problem went away when he got an aftermarket TB but beyond the devices attached to it, i don't know what to think.

11-17-2009, 01:46 PM
use the coil wire to check for spark or stick a old plug in a plug wire, the electrical connector is far enough up inside boot it may not arc

dan fitz
11-23-2009, 04:25 PM
well, with a visit from my geo buddy who brought a spare intake manifold from a 3 cylinder with throttle body etc. attached, we have fixed the problem. at some point we had our spark back but still not the slightest kick while cranking hot, so he pulled the injector connector out while i was cranking and pushed it in and out rapidly, with the result being that it started! the injector was sticking when it was hot; the one in the 3 cylinder TB had the same numbers so i switched it out and it started when hot just fine. in retrospect the symptoms make perfect sense; the injector is getting cool air flowing past it as long as it's running, and is still relatively cool when first shut off, and will start up, but after 10 or 15 minutes of sitting still the whole TB heats up as temperatures even out under the hood, and nothing happens till the magic temperature is reached an hour later. also explains why pouring cold water on all the suspect electronic items never did a thing, because of course i never took the air cleaner off and applied a piece of dry ice..... so i don't wish you the same symptoms but if you have this problem, it seems the injector can be fussy when hot, and "jump starting" it like my friend did will let you know if it's bad or not.

11-24-2009, 06:26 AM
hi dan fitz,

good troubleshooting and i appreciate your analysis. not sure i'm understanding completely. i've never done any injector work. was it faulty? so there was never a problem with the spark? was there an interrupted electrical link between the injector and the ignition?

dan fitz
12-02-2009, 03:08 PM
hi red; the injector was faulty, sticking when hot, but as far as the spark goes, twice i verified no spark when cranking under the problem conditions. with all the parts we switched out, it's possible we fixed the spark at some point and then the injector problem was revealed. but with the ECM's internal protocols and algorithms, who knows if the spark was turned off because the injector wasn't opening? there's probably some people out there who know exactly what the ECM would do in a case such as this but i am not one of them. it's kind of like if the fuel pump failed and the ECM told the engine not to even crank because what's the point if there's no fuel being delivered to the system. prior to fuel injection and computer control figuring out what was at fault was fairly straightforward but those days are over. that said, i take care of about 15 cars for a non-profit and really never have any issues with the ECM's, injectors, etc., so when they work, they work well, but when they don't, the headscratching begins.

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