73240z Posted March 1, 2008 Share Posted March 1, 2008 Ok, after countless hours in the garage trying to brainstorm and come up with the possible reasons my car is not starting, I have run out of ideas. I put in a rebuilt LS1 last summer and never got it to start up. Here is the problem: When cranking, the engine will crank without firing for the first couple cranks. Then, it will start to fire in each cylinder, one every couple strokes. Once I have been cranking it for a little while, there is firing in all of the cylinders, but its very rough and it wants to die out. The longest I can get it to stay running is only about 2-3 seconds, then it will cut out. It will also not start at all when I just touch the gas, as if more air is making it cut out completely. Right when I start it, it will fire a cylinder and a few others with no problem, after that it will just die out slowly. I have a custom harness and re-flashed computer from Speartech, but before I got the harness, I had the stock harness and un-flashed computer and it was doing the same thing. I know my harness and computer are good. I checked compression on all cylinders and it all checked out ok. I checked my grounds, all the sensors are plugged in, I checked plugs and plug wires, all looked good. When I checked the plugs, they were somewhat dark and a little wet. I am sure all my wiring is good, cause I get spark on all cylinders, and all my injectors pulse. Each cylinder does fire and gets good spark. I also checked to see if it was reading any codes, and no problem codes came up. I am out of ideas and am getting depressed because so much time has gone in, and its still not working. Please, if anyone can help pinpoint this problem it would make my year. this has been the one thing that has kept this car from being on the road. Please, let me know what your thoughts are and if you have any suggestions. Thanks, John Quote Link to comment Share on other sites More sharing options...
ColtGT4g63 Posted March 1, 2008 Share Posted March 1, 2008 Who did the rebuild? You, or a machine shop? By any chance during the build was the tone ring on the crank left off? Left half off? wrong one installed? Are your crank and cam sensors good? I believe the LS1 has the crank sensor in the side of the block, and the cam sensor at the top in the back. (correct me if I'm wrong here.) Possibly bad sensors? Did it run before you did the rebuild? Did the motor ever run before? More details would be useful. Quote Link to comment Share on other sites More sharing options...
73240z Posted March 2, 2008 Author Share Posted March 2, 2008 I bought the motor from a shop that rebuilt LS1's. As far as the cam and crank sensors, if the crank sensor was bad, I don't think it would fire, or it might fire, but very randomly. I unplugged the crank sensor and it made a big difference, and didn't really fire at all. The cam sensor didn't do much when I unplugged it, but I think they are ok, cause the engine will fire, and run just for a couple seconds then cut out slowly. If I just barely press on the gas, it wants to cut out completely. I played with the vacuum lines and blocked of the ones just behind the throttle body and it ran smooth just for about 2 or 3 seconds then cut out. This makes me wonder if it is an air or fuel issue. It almost like all the air is getting used up in the intake, and once it gets all sucked out, it just dies. As far as the engine before the rebuild, I'm not sure of the history of it, as I bought it from the builders as a rebuilt engine. All the sensors cam with the motor, so it could be a sensor that was bad and got put on the engine. I just don't have any idea which ones. I have played with them all, and disconnected, started, and reconnected them all. Tried different ones, and no luck. Any other ideas? Quote Link to comment Share on other sites More sharing options...
gmed Posted March 2, 2008 Share Posted March 2, 2008 Always do the basic stuff first, put in a new set of plugs. More than one person has chased their tale thinking they had major problems when it was just a badly fouled set of plugs. You dont state how old the plugs are but even if they are new and are dark and wet from being gas fouled they will cause they will not fire correctly even if they are getting the proper spark from the coils. Quote Link to comment Share on other sites More sharing options...
jasper Posted March 2, 2008 Share Posted March 2, 2008 Have you put a fuel pressure guage on it? Quote Link to comment Share on other sites More sharing options...
80LS1T Posted March 2, 2008 Share Posted March 2, 2008 Have you put a fuel pressure guage on it? I am thinking the same thing. Is your fuel pump running while cranking? And what is the fuel pressure while cranking/sorta running...? Guy Quote Link to comment Share on other sites More sharing options...
73240z Posted March 2, 2008 Author Share Posted March 2, 2008 I changed the plugs out already, thinking there could be a couple bad ones from the rebuild. So all the plugs are new and gapped evenly. I have a holley fuel pump right after the fuel cell and a aeromotive regulator just before the fuel rails. I have the psi set at 58. My fuel pump is wired independently from the rest of the harness, so it has a constant currently in ignition-on. My pump is definitely working, I took off the fuel line from the fuel rail and there is definitely fuel that is being feed to the rails. I just am really confused why it will run for a couple seconds then just cut out , but if I go to start it right back up again after it dies, it will take a couple cranks then do the same thing. Quote Link to comment Share on other sites More sharing options...
Phantom Posted March 3, 2008 Share Posted March 3, 2008 Which LS1 do you have? Is it the one with a fuel control based on demand or does it work with a return line? Wet plugs indicate a rich system. Have you had a chance to see or smell your exhaust? Does it look/smell rich? I'm not convinced you have a sensor or ECU problem. Mine was straight-forward being out of a '98 Z28 Camaro it used a return line just like my 280z. Also, are you sure your tank and fuel filter is clean? Quote Link to comment Share on other sites More sharing options...
73240z Posted March 3, 2008 Author Share Posted March 3, 2008 My LS1 has the fuel return line, I am using the stock fuel rails, but took out the schrader valve. As far as the plugs, they are dark like I said, and a little gassy last time I checked (when I changed them 2 weekends ago). The exhaust is pretty dark and made my clothes smell after I had been trying to start it and was working on it for about an hour... So, yes, rich. I am almost positive my ECU is good cause I sent it into Speartech to have it re-flashed and got it back. One of the sensors could possibly be the problem, but I only have had access to a scan tool that reads codes and not engine rpm or sensor details. I have tried unplugging just about every sensor, one at a time and attempting to start it to see if it made an difference (better or worse), but not much luck. My fuel filter is bran new, and I have new fuel safe enduro fuel cell. I know fuel is good cause I filled up a jar with gas pretty quickly (line feeding the fuel rail). Any specific sensor that would cause it to cut out but still allow it to fire and run for a solid 2-3 seconds? Any other thoughts guys? Quote Link to comment Share on other sites More sharing options...
80LS1T Posted March 3, 2008 Share Posted March 3, 2008 What about the timing? Not ignition but the cam to crank timing? Are you sure that its set right? Wrong timing will cause issues like this. Also has the engine been broken in yet? Maybe the cam has some lobes worn off from a bad break in procedure. You could pull the valve covers and see if all the rockers are moving the same amount. Of course you said that the compression was good so this is probably not the case. So you have not actually checked fuel pressure while cranking? Even if you have it wired independently I would still check it while cranking just to be 100% sure you have it wired correctly. You said you have it wired for ignition power but unless you have it wired to a 12V while cranking powe source it wont turn the pump while your tring to start it. Guy Quote Link to comment Share on other sites More sharing options...
ColtGT4g63 Posted March 3, 2008 Share Posted March 3, 2008 Try un plugging the MAF, Maybe see if it will run in "limp home mode" ? Fuel pressure gauge wouldn't be a bad idea either. If you have fuel pressure through out cranking, start up, and dying. You can rule the fuel pump / pressure out of the equation. Quote Link to comment Share on other sites More sharing options...
73240z Posted March 3, 2008 Author Share Posted March 3, 2008 80lt1, I'm hoping the people who built my engine got the crank/cam timing right, but I haven't checked it, as I am hoping for it being an external problem. The engine hasn't been broken in yet, it hasn't had a chance... can't start it, I swapped it in and it hasn't been running yet. As far as the fuel pressure while cranking, I did check that yesterday and it stayed right at 58-60, where it was when I'm not cranking. While it fired and ran for the 2-3 seconds it also remained around 58. coltgt4g63, I thought about maybe a sensor malfunctioning but still working and sending values that were either very high or very low, causing a rich mixture. I also have heard of someone only being able to start their car when the MAF was unplugged and it was a bad MAF. I thought I tried starting it without the MAF plugged in once or twice, but I will give it another shot and see if it does anything. The engine should be able to run just with the TB (take off the intake). I'll unplug the MAF and give it a shot. Are there any vacuum lines that if blocked off would cause it to cut out? The only line I have going to the intake is the one on the back (MAP-valve cover) and the one on the front (valve cover-Intake just behind TB, pass. side). All the others on the TB and intake are blocked off. Ideas? Quote Link to comment Share on other sites More sharing options...
linchpin360 Posted March 3, 2008 Share Posted March 3, 2008 in my experience that sounds like it could be a maf for sure. my rx7 did the same thing when i first got it. Quote Link to comment Share on other sites More sharing options...
73240z Posted March 3, 2008 Author Share Posted March 3, 2008 alright, I will try starting it without the MAF plugged in and see if it does anything different. Hopefully its a bad MAF. If it is bad, I will have learned not to buy sensors on ebay... Any other possibilities other than the MAF? Quote Link to comment Share on other sites More sharing options...
80LS1T Posted March 4, 2008 Share Posted March 4, 2008 If you have a large vaccum leak after the MAF it could cause a very rough idle and possibly cause a hard start issue. Unplugging the MAF will force the ECM to default to speed density. If it runs normal with it unplugged then you need a MAF(assuming your wiring is good of course). Guy Quote Link to comment Share on other sites More sharing options...
73240z Posted March 4, 2008 Author Share Posted March 4, 2008 alright, I will give it a try. I am probably in the small percentage of people who hopes their MAF is bad. Thanks 80LT1, I will let you know what it does. It will be a little bit before I give it a try, I am at school this week. Quote Link to comment Share on other sites More sharing options...
VinhZXT Posted March 4, 2008 Share Posted March 4, 2008 My LS1 has the fuel return line, I am using the stock fuel rails, but took out the schrader valve which valve is this? Are you talking about the one sitting on the fuel rail? The 97-98 models used the FPR on the fuel rails. Just curious did you install a FPR? This sounds like a fuel pressure problem. I highly recommend you install a FP gauge and check it out before checking other problems. GL. Quote Link to comment Share on other sites More sharing options...
73240z Posted March 4, 2008 Author Share Posted March 4, 2008 VinhZXT, I was refering to the schrader valve on the end of the fuel rail, on the fuel return end. I took it out because I was using an -AN connection. The fuel pressure regulator I am using is an Aeromotive with a fuel pressure gauge just before the fuel rails. It is set at 58-60 and remains there while it fires. Quote Link to comment Share on other sites More sharing options...
VinhZXT Posted March 4, 2008 Share Posted March 4, 2008 Can I see a picture of your engine and the fuel set up? I am very confuse about your setup based on what you said. You removed the schrader valve to install the AN fitting but what are you connecting to here? Normally people just remove the schrader valve to install the fuel pressure gauge. Also you said you use the fuel rail with a return line and you installed an Aeromotive FPR before the fuel rail. This means you must have a return line connect from this FPR to go back to the tank. What did you connect to the return line at the fuel rail? Are you happen to use the 97-98 C5 PCM? Quote Link to comment Share on other sites More sharing options...
73240z Posted March 4, 2008 Author Share Posted March 4, 2008 Alright, this is an older picture, but the fuel pressure regulator and gauge are just before the fuel rail inlet now. Quote Link to comment Share on other sites More sharing options...
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