Car won't start, cranks but backfires/tries to start

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Thread: Car won't start, cranks but backfires/tries to start

  1. #1
    Garage Queen Club dre99gsx's Avatar
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    Car won't start, cranks but backfires/tries to start

    Did a rebuild and buttoned her back together as best as I could. I can crank, I get 42psi fuel pressure and the cylinders are "wet" of fuel (I do air it out here and there to keep it from flooding). While cranking, it will try to start and backfires.

    Still on stock ecu/maf. Verified cam timing is in spec on these cams. Triple checked all connectors, although some are not connected to anything, they mostly seem to be evap or vsv crap that never existed on the car to begin with.

    I get oil pressure on crank as well. Check most of my fuses, everything looks good. Any ideas? I'm wondering if I missed something that is "obvious" when folks rebuild these motors (like swapping cam signal 1 and 2 with each other, etc)? It almost feels like its firing out of time or sync for some reason.

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  3. #2
    feeding your habit 98mkiv's Avatar
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    crank sensor is sligtly magnetic, check to see if it has any metal debris stuck to it... Don't know if it would cause this problem, but maybe.

    -M

  4. #3
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    I'd double check the crank/cam sensor connectors and the big orange one near the ecu. You have to tighten that one down with the white plastic arm, a lot of people forget to do that. Double check all your grounds straps are connected too.

  5. #4
    Garage Queen Club dre99gsx's Avatar
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    Ok. I had cleaned the crank sensor pretty well before reinstallation. Should be crisp. I will run the tests to verify both cam and crank sensors are outputting.

    As for the ecu, it hasn't been touched or removed. The orange connector should be tight from factory?.

    I am going to go through all of the grounds. The damn electronic toyota manual doesn't show EXACTLY where some of those grounds went, I just assumed in some locations.

    Also, no CEL codes listed.

  6. #5
    Garage Queen Club dre99gsx's Avatar
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    I checked the basic grounds (ohmed them out as well). Block and head are each grounded to their points on the chassis. Ground battery cable ground there as well. Car cranks with no issue (battery has charge, starter circuit works well).

    I ground out each coil/spark plug, and each one generated a spark (grounded to the TPS bracket). This would signify the ECM is getting some signal from both CAM and CRANK sensors. I also double checked ecu codes, if the sensors were bad, it should have detected them by now. I may still ohm all three sensors.

    Out of every 10 seconds of cranking I get about 2 or 3 silent "puffs" as if some explosion is happening, but nothing worthy of starting. This is very strange.

  7. #6
    Garage Queen Club dre99gsx's Avatar
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    Another update:

    Got about 120psi compression all 6 cylinders (which is ok. cold motor, rebuilt, fresh head, things haven't worn in).

    I would like to know if anyone can try this for me and get some data. Firing order should be 1-5-3-6-2-4. I lifed all 3 coil pack sets and removed all spark plugs, but re-inserted them back into the coils, and layed them ontop of the valve cover.

    Turn the key on to run (dont crank), leave all fuses in. Grab a comfortable wrench and start turning the crank pulley by the bolt. Here is what I found:

    Starting at CAM and CRANK all at they're #1 tdc marks: #5 spark, #3 spark, fuel injector starts to spray, I can then turn the crank almost 2 full revolutions with nothing happening, then #2 fires, #4 fires, #1 fires, #??? (I missed where this one came from, but heard a spark), #3 fires, #6 fires, then Fuel spray, followed by another fuel spray ( very freaken wierd), then another 2 full crank revolutions with nothing, then #2, #4, #1, #5, #3, Fuel spray, another crank revolution with nothing, then #5, etc etc... This looked very odd, and I wanted to make sure this test would work as I don't have a scope handy.

    I checked all fuel inj clip wire colors and all matched as per mkiv electronic shop manual(incase I flipped an injector wire somewhere).

    The intake cam has the two tabs, thus I know this is the HKS intake cam. I haven't ohmed out any cam/crank sensors as of yet.

    Another thing I noticed was the crank timing star gear has a concave shape two it. I installed it with the concave facing the back of the motor. Don't know if this is an issue.

  8. #7
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    happened t me when i got back from the desert sounds really stupid and i over looked it but did you by any chance chec k you fuel level mine would come up to about 40psi then while cranking steadily fall off. my roomates ran my car outta gas man was i fired up about that. just tryin to help hope you figure it out

  9. #8
    DRiFTT 1JZ_Cressida's Avatar
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    ^^lol, thats something we would never decide to check, i had something like that, my as needle stopped working and it read 1/4 tank, cranks like it wants to start like normal.....just when a friend came over, he came with gas and i did'nt no why, threw it in the tank and hit me some slaps and it started the car tho

  10. #9
    Garage Queen Club dre99gsx's Avatar
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    Hmm. Gauge reads half a tank of gas. Fuel pressure remains stable at 40psi while cranking as well

  11. #10
    Chem Eng. rules blancovich's Avatar
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    Something similar happened to me a year ago but it was because I had a bad connection in the BCC. It was actually a Turbo Pressure Sensor Failuredue to a bad connection.
    Do you have a BCC? Did you mess with it?

  12. #11
    Garage Queen Club dre99gsx's Avatar
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    No BCC. No ecu either of anything.

    btw, I found the problem, and SHE STARTED! After inspecting all 3 sensors, I determined that the crank sensor was the only unknown. I compared the intake cam with a stock intake cam to verify the cam sensor tabs were in the same locations, 180deg apart. They were. Since the sesnors and wiring all checked out, I then proceded to verify that the crank timing plate was in the right location. Well, it wasnt. After removing the timing belt covers, I noticed the timing belt was not using the entire crank timing belt gear. 1/8th of the belt was sticking out past the rear end of this gear.

    Turns out the timing plate behind the gear was not pressed into the gear. I thought you slide on the plate, then the gear, and they press into each other (as long as the plate's tab lines with the gear's groove). I guess not. I removed them both and pressed them together in a vise, heard a click, and realized this could have been the issue.

    The crank sensor was seeing erratic signals as I was turning the crank. I'm sure if I had an oscilloscope handy I could have caught this quicker, but through process of elimination, gold was scored.

    Thanks for the help. She fired up and idled like it should. 80psi oil pressure (cold), fuel pressure was good, etc etc.

  13. #12
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    Glad to hear it started Dre! Like I told you yesterday I suspected it had to be a problem down there with that crank trigger wheel.

  14. #13
    Garage Queen Club dre99gsx's Avatar
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    Yeah as soon as you mentioned the trigger wheel, it made me remember how it was hard of a time I had keeping it on the crank gear. I should have pressed that sucker on in the first place. The manual doesn't really clarify on it either. Anyway, thatnks for the tip.

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