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No Start & Big Backfire....Help?

OK, #1303 has been sitting for quite a while. I am just now starting to get it ready for the autocross season, so yesterday I fired it up for the 1st time in many months. It fired right off (with a jump start) & ran great for a about 10 minutes as I let it idle. Then, I went to move it & every time I gave it any more than say 20% throttle it would bog down & run rough. It kinda sounded like a 2 step set at 2000 RPM. If I backed out of the throttle slowly it would settle back to a normal idle. It was getting dark, so I just idled it back into the garage, shut it off & thought I would look into it more today. Well, this morning I go to try & start it (pretty cold out, 29-30 degrees), & it cranks over quite a bit, coughs a couple times during cranking, but won't fire. I try it again, only this time (& every time after) it won't even cough while cranking, but as soon as it stops cranking I get this LOUD backfire out the exhaust. The backfire actually happens AFTER the engine stops cranking. Any ideas guys? I took a quick look under the hood, but everything seems in place. Just thought I would post here before I start digging into the car with no real direction. Thanks in advance.
 

iceman69510

Turn Right Racing
Staff member
Joined
Mar 5, 2001
Messages
10,968
Location
Michigan
Well, you're getting fuel if it backfires. Compression if it is pumping, so need to get spark.

Check/change the plugs?
 

1990ggsxnj

Well-known member
Joined
Nov 21, 2008
Messages
525
Location
Blackwood, NJ
If all else fails, I would also take a quick look at TDC on the cams. If anything happened where slippage occured, you could be sparking when you shouldn't be, and coincidently not sparking when you should be. Even though at that point your pistons and valves are hammered, those injectors are still spitting and plugs firing.
 

I checked the timing belt & all looks OK....it ran well yesterday in my driveway so I was pretty sure it didn't jump teeth or anything. I also went & checked all the electrical connections under the hood as well, but everything seems in order. Once again, the car has been sitting for 5 or 6 months, & before I parked it then car ran great. Does this sound like a possible computer issue? I put a used but rebuilt Eprom ECU in it about a year & a half ago after my original one failed....after being rebuilt & capped can they go bad again? This problem has me very concerned, I have never had a car backfire like this....after the engine has stopped cranking. It is LOUD, like a gun shot, I'm afraid it's going to hurt something. Logically thinking it seems like fuel is building up in the combustion chamber but the plugs are firing at the wrong time??? If that's correct, then maybe ECU, CAS, TPS??? I'm guessing now, just not sure where to go from here. Thanks again in advance for any help.
 

fivestardsm

Well-known member
Joined
Sep 8, 2006
Messages
1,699
Location
Middle, Michigan
I hope you find out what is wrong!!
I have a motor that I pulled out of a wrecked car that ran great when I bought it. After I pulled the motor out and it sat for roughly a year, I put it in another car that I had picked up and it ended up not wanting to run right. (all the same symptons as yours) Well I worked on it for 2 or 3 weeks straight and changed EVERYTHING!! I checked the timming 3 times and all the sensors were changed countless times along with 4 or 5 different ecu's. And then I changed the entire fuel system all the way from the tank up, 4 or 5 rails and a can full of different injectors. Along with the pump relay also.

Well I finally figured that it was something with the wireing harness and let it sit for another 6 or 8 months.Then I picked up my second galant, and knowing that the motor "was" a good runner, I pulled it out and put it into my galant wich I also know was a running car before the belt snapped. It did the same thing. So I pulled it out and threw it in the motor shed. That is where it has been for the last 3 years. By the way, i did put another motor in the galant and it ran perfect.. until it crankwalked that is.

So I really hope you figure out what is wrong because Maybe it will help me!! /ubbthreads/images/graemlins/wink.gif
 

Since it's night time & freezing outside, I'm not going to mess with it until tomorrow, but I keep thinking it over in my mind. It's as if there is no spark while the starter is engaged, or maybe when the ignition switch is turned all the way to "start". But then as the key is released, it gets a quick spark since the engine is still slightly turning (& the ignition is still "on") & then BANG....it lights off the fuel in the chamber. I will confirm if there is spark while the engine is turning over tomorrow, but does that sound like something you checked on your car? The other thing I have been thinking is bad fuel. I run 100 octane unleaded through it, but I think it's like a year or more old. The fuel will obviously fire, the backfire proves that, but maybe not in smaller amounts....I don't know, I'm guessing at this point. This has me so puzzled, this car has always ran sooooo well.....I remember reading threads on here in years past thinking, "man I must have a good car because I don't seem to have all the problems other's seem to have". Guess I shot myself in the foot thinking that lol /ubbthreads/images/graemlins/banghead.gif Well, I sure hope my problem isn't what you have, I don't have the time to rip this car apart & put it back together again chasing a gremlin. Anybody else have any ideas??
 

fivestardsm

Well-known member
Joined
Sep 8, 2006
Messages
1,699
Location
Middle, Michigan
Quote:

"It's as if there is no spark while the starter is engaged, or maybe when the ignition switch is turned all the way to "start". But then as the key is released, it gets a quick spark since the engine is still slightly turning (& the ignition is still "on") & then BANG....it lights off the fuel in the chamber"

This is actually caused because when you are letting off the ignition, The injectors stop, but there is still a spark discharge with a little bit of extra air into the mixture and it ignites all the exsess gasses that are floating around.

EDIT: Please dont let my diagnose of all the things that I did discourage you or make you think that you dont need to check the same possibilities.
I too hope tht your problem isn't a severe one. As for the gas, it is possible that it could be a problem, but if its only 5 months old and 100 oct.... I'm not sure. /ubbthreads/images/graemlins/dunno.gif
 
Last edited:

brisvr4

Well-known member
Joined
Feb 13, 2004
Messages
955
Location
brisbane australia
Is the car throwing a cel at all?
I'm wondering if the ecu temp sender may have chosen this exact moment to die on you.
That would explain the cranking problem but may not explain the backfire?
 

Andy_S

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Joined
Jan 30, 2007
Messages
982
Location
Shithole Wisconsin
I had a POS talon I paid $100 do that too. Was the CAS failing out on me. Crank, crank, crank, stop... BANG. Blew half the junk cat out of the exhaust. Prior to discovering the CAS problem, I changed the coil pack, ecu, plugs and wires, and probably more with no avail. Needless to say my junker got parted because the body rotted in half. CAS did solve the problem though.

I would replace the CAS. They are cheap and while your at it, you might as well put a blacktop in there.
 

OK, I figured a couple things out & I'm making some headway, but still can't get it to start. It's got spark while the engine is cranking, & it appears to be getting plenty of fuel. I pulled all the plugs & not only were they pretty black, but they were wet with fuel. I must admit though, I have not heard the pump humming with the key in the run position & the engine not running, should it be? I can't remember, I know I've heard it when the engine is running. There definitely seems to be fuel in the engine, so I would think it is working.... Yes Steve, the backfire does seem to be caused by a quick spark AFTER the key is released from the start position. I think you are right, the injectors quit but there is still a slight rotation of the engine, enough to fire the plugs becuase the ignition is still "on". I'm guessing it pops because the engine has stopped turning so the pressure is forced out the exhaust of whatever valve is open. Just my theory, but I definitely noticed a spark after the key was released as I was checking it. So, now as I try to start it, I make sure to rotate the ignition switch quickly to the off position rather than the run position. Since I have been doing that, no backfire. I did try spraying some starting fluid into the intake, & with the throttle wide open during cranking I did get a couple coughs & sputters like it was trying to fire. So, at this point I am really leaning toward bad fuel, so I think tomorrow I am going to try & drain the tank & put some fresh 100 unleaded in there & see what happens. But before I do, I am definitely going to replace the CAS as I have a spare. No, throughout this whole ordeal, no CEL, but in all honesty I can count the amount of times this car has triggered a CEL on one hand. Considering it has a stock ECU & I run a lot of fuel & boost through it, you would think I would see them all the time. Aspod, what is a "blacktop"? As for the MAF, I am running a GM unit with the translator. I checked the connector on it & it seems OK, could it be the connection where it's tapped into the CAS wire? Anyone know how to test the GM MAF to see if it's working properly? Sorry guys for all the questions & trouble, once I get this thing going I plan to document the entire autocross buildup for the benefit of everyone....just need it to run first /ubbthreads/images/graemlins/banghead.gif Thanks again for the help.
 

Kenny_Kline

Well-known member
Joined
Dec 27, 2007
Messages
789
Location
Seekonk, MA
Your issue is your running rich. WHatever reason that is, thats your problem. I would check calibration of the MAFT and/or check ALL wiring for it. It really does sound like a bad MAF setup. Are you running an SAFC? Also check that wiring to make sure nothing happened with the signals.

The reason why I am leaning towards a MAF issue is because the same thing happened to me. I hooked up a logger and seen the air meter read 0hz meaning it was getting no signal from the MAF to the ECU. The SAFC also has a hz reading to see what the MAF is doing so if you dont have a logger (which you should) you can use an SAFC. My issue ended up turning to be a disconnected wire on the AFC harness (MAF input wire) but still, a 0hz signal for the MAF would mean its messed up somewhere within that system and thats exactly what that sounds like.

To be running that rich, its either what i described above or your running crazy high fuel pressure or you have all 4 injectors hung open (not pulsing). Really take the time and look into the things I mentioned above. I am willing to bet its one of the things I mentioned.
 
Last edited by a moderator:

Andy_S

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Joined
Jan 30, 2007
Messages
982
Location
Shithole Wisconsin
Quoting race2win:
Aspod, what is a "blacktop"?



CAS from 93-94 dsm (maybe more?). Its a hall-effect sensor that gives a better quality signal. 2g guys with 6-bolt swaps use them to help combat the "random misfire."
 

turbowop

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Joined
Apr 29, 2001
Messages
11,972
Location
Yakima, WA
Quoting race2win:
I have not heard the pump humming with the key in the run position & the engine not running, should it be?



No. The pump doesn't run unless the CAS is spinning.
 

spooling92vr4

Well-known member
Joined
Jun 7, 2005
Messages
2,511
Location
long island, NY
had the same problem with my galant not too long ago the coolant temp switch had a bad connection in turn the car would not fire and fouled out the plugs. the switch fails and reads -30 something and the car is a real bitch to get started

check the connections there, its possible the switch could be bad... if the car has spark fuel and injector pulse it should start.
 

spooling92vr4

Well-known member
Joined
Jun 7, 2005
Messages
2,511
Location
long island, NY
Quoting brisvr4:
Is the car throwing a cel at all?
I'm wondering if the ecu temp sender may have chosen this exact moment to die on you.
That would explain the cranking problem but may not explain the backfire?



I just noticed after i posted, 100 bucks its that though
 

OK, here's an update on this frickin car...... /ubbthreads/images/graemlins/mad.gif I read another post on here where someone else was having similar issues, & the coolant temp sensor was recommended to him as well. That seemed to cure his problem, so today I checked it. Sure enough, the wires going into the plug were all cracked & exposed. So, I put another sensor in from #733/1000, & I also cut the plug off & used nice fresh small female spaid connectors & shrink wrapped it up all nice. Still no start!! Backing up a little, this week I have also changed the CAS, coil pack, & power TR unit. When going to change the CAS, I noticed the nut holding the side where the brace is was loose (the brace that goes to the throttle body). The other nut was tight, & the CAS didn't appear to have been moving at all, but I thought I had found the problem. NOPE! My problem now is that I have had the 2 different CAS on it a couple times, & since it won't start I have no idea if it is on correct or 180* backwards. What sucks is now with everything else I try, I have to pull the CAS & rotate it just to make sure I don't rule anything out. Now, these parts I am using are from my other GVR4, #733/1000. This car has been sitting for many years & is pretty much a parts car at this point, but I figured what's the chances of it's parts being bad too....I don't know, maybe one of them is, I just have no idea which one. So, I'm not sure where to go from here. I do want to try a new coolant temp sensor, but my local auto parts stores don't have any in stock. Plus, the picture they show for it doesn't match what the OEM one looks like. Any ideas on this? Should I wait & get it from the dealer? Problem is the nearest Mitsu dealer is like 2 hours from here.... I also want to try another ECU just in case. I know that when my original ECU took a dump it had similar symptoms. The ECU that is in the car now is also from #733, but it has a sticker on it saying it was rebuilt in 2000. I just took it out of the car & took a look inside....no trademark fishey smell or obvious board damage, but who knows. This car has me soooo pissed off right now.....it sure makes me miss the Miata autocross car I had. I was so excited to get this project going this week & do things like changing the brakes, re-routing the intercooler & pipes, change the turbo, etc.....all to get it ready to win autocrosses....but now I have wasted a week chasing a gremlin with no end in sight, I could have almost been done with everything else by now /ubbthreads/images/graemlins/banghead.gif This car is about to get parted out & I'm going to buy another Miata.......
 

Andy_S

Well-known member
Joined
Jan 30, 2007
Messages
982
Location
Shithole Wisconsin
Have you hooked up a logger? That will show any discrepancies in the sensors quick. Still sounds like a CAS to me. Have you cleaned any of the ones you tried?
 
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