niner11 Posted December 12, 2007 Share Posted December 12, 2007 I installed 2.88 firmware the other day and the new x-tau enrichments are pretty impressive just using the defaults for accel and decel. Also, a HUGE improvement with how MAP is now measured by MS. I have a mapdot threshold of about 30 and the sampling rate is something like 25ms.....the recommended default. Works really well My setup is a stock turbo (82) longblock with a t3/t04 running MSII for spark and fuel. Pallnet fuel rail with 33lb injectors at 50psi, 240 TB and TPS, FMIC, MSD, etc. The car runs great and is currently set at a max of about 12lbs of boost. Here is the problem, the first time that I loaded the new code 2.88 there were some important X-Tau settings that didnt get carried over into Megatune. I wound up recreating my MSQ by hand and later imported my AFR, VE and Spark numbers from saved Vex files. Seemed to work and the defaults showed up....the car ran perfectly. There are a lot of new settings in this code but I can't for the life of me figure out what is going on right now. Car starts and runs great but a few moments after start it sometimes goes way lean....from about 12.5 to 15 or so. I looked at the PW's and they are not changing as the car goes through these oscillations and fuel pressure stays the same. For the most part the lean condition will go away in a few mins or 10 mins at the most. This seems to narrow it down and I was thinking it was a fuel issue but by shutting off the electric fan I can sometimes make these lean oscillations go away immediately. Strange This got me thinking and I took another box that I have for a backup and put my old 2.687 code on it and currently have no more oscillations. Tomorrow I will swap both boxes in and out and try to duplicate what is happening. Will also get a few datalogs. Wondering if anyone else had had a similar problem. Some ideas: warm fuel in the rail (not very likely at these temps) Contaminments in the fuel, rail or injectors that behave differently at diff pulwiths some type of interference with the fan on, but why does this only happen sometimes? Is this prob specific to v2.88, wondering if anybody else has had a similar problem. Thanks, any ideas would be appreciated. Quote Link to comment Share on other sites More sharing options...
niner11 Posted December 13, 2007 Author Share Posted December 13, 2007 Here is a datalog of a hot restart with the afr numbers changing. It does take a few minutes for the afr's to start leaning out. Looking at the datalog I cant figure out why. Interestingly enough, I turned my electric fan off at one point and it seemed to have a stabilizing effect on the oscillations that I have been seeing. When I turned the fan back on (via the fidle port) it had no negative effect at all. Since the pulse widths don't seem to be responsible for the changing AFR's at idle I'm wondering if it might be the injectors. Fuel system is free of debris and has a constant fuel pressure. Right around record 715 or so in the datalog the problem begins and it ends around 2049. MSQ with288.zip Shortcut to datalog200712131519.xls.zip Quote Link to comment Share on other sites More sharing options...
dum-bass Posted December 21, 2007 Share Posted December 21, 2007 Wow, that is interesting. I have been having the same problems and at first I thought it was a way too rich after start enrichment but when I datalogged it, it showed going way lean to 16, 17:1. It goes away after the ASE indicator is off. I think it might be a case of going so rich that the wideband thinks it is lean... Quote Link to comment Share on other sites More sharing options...
niner11 Posted December 21, 2007 Author Share Posted December 21, 2007 There has been some talk on the megasquirt forum of an issue with heat soaked temp sensors causing lean restarts. One option is to mount the sensor on a charge pipe just after the intercooler but before the TB to keep intake manifold heat from soaking the sensor. I will try several different things this week including playing around with the MAT correction tables in Megatune. It may just be the fuel rail heat soaking. This problem isn't specific to v2.88 but on my car the idle suffers more than previous firmware (2.687). Probably will try firesleeve on the fuel lines over the intake and some phenolic spacers on my aluminum fuel rail mounts to limit the heat soak. Dum-bass, if you aren't sure if its lean or rich with the missfire at idle you can just use VE in the tuning pull down and richen or lean the idle "box" that the car is runing in. I checked and if I richen the mixture while I'm having these wild AFR oscillations the car smooths out and runs great. Since the PW's don't seem to change much and the fuel pressure is the same at about 50psi it seems like the problem is due to hot fuel (vapor lock). Just to rule out that this lean condition is being caused by an inaccurate temp value being sent to MS I thought I'd connect a different temp sensor that is reading free air next time I have the hot restart problem. I'll post an update when I figure this out Quote Link to comment Share on other sites More sharing options...
niner11 Posted December 29, 2007 Author Share Posted December 29, 2007 I played around with another IAT sensor this week. When the car would start to run lean on a warm restart I disconnected the temp sensor and plugged in one that was sampling free air....made absolutely no difference. I also tried different MAT corrections with the same result. For now I will try to insulate the fuel lines and rail from exhuast and turbo heat and see if it has any effect. BTW, I have very few oscillations in AFR when I use EGO control to smooth out these warm start issues. Quote Link to comment Share on other sites More sharing options...
Zed2k Posted February 24, 2009 Share Posted February 24, 2009 I have the same type of problems too, so keep us updated I had the wideband connected and saw 17-19 afr and was running very lumpy I have fitted another heat shield to the turbo area of the engine with little effect, so may wire a small fan to run across the injectors and fuel rail to see if this helps keep the rail cooler. I'll let you know the results to. Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted February 24, 2009 Share Posted February 24, 2009 It's an old thread, but I always attribute "lean hot start" to vapor lock in the injectors or rail. There are some tricks you can play with the intake air temp sensor. Get it to pull up the pulsewidths when the IAT is ridiculously high after being parked hot. Quote Link to comment Share on other sites More sharing options...
Zed2k Posted February 25, 2009 Share Posted February 25, 2009 Can you let me know the tricks please? as these lumpy restarts are the only problem I have with my setup. apart from that it's great Quote Link to comment Share on other sites More sharing options...
Zed2k Posted February 27, 2009 Share Posted February 27, 2009 Right, I have moved the IAT sensor to the Pallnet spacer just after the throttle body I'm thinking the plastic spacer must conduct less heat so I'll let you know the results tommorow. Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted February 27, 2009 Share Posted February 27, 2009 You can create a fuel correction chart so that it goes rich when the IAT reads really hot, say 140F+. The IAT should only get that hot during heat soak and you can help correct the AFR's to compensate for some vapor lock at hot start. It should work....I think. Quote Link to comment Share on other sites More sharing options...
Zed2k Posted February 27, 2009 Share Posted February 27, 2009 I'll let you know how it goes in the new position first then may look for some guideance for some more IAT settings if this still play up. Quote Link to comment Share on other sites More sharing options...
Zed2k Posted February 28, 2009 Share Posted February 28, 2009 Right, well, I moved my IAT sensor from the inlet manifold, as I was getting bad lean hot starts and so after reading all the hot soak issues in that position I have now relocated it to the plastic ( Pallnet) spacer, In this position, it gets far less heat soak and so spent alot of the day running the car letting it sit and watching the IAT temp. Once upto normal running temperature, ticking over, it stays around 46 degress C when turned off the max it reached in the spacer position was 61 degrees. when started it still turns really lean 16-17 AFR so. After cygnusx1's comments, I looked into the IAT correction table and put some rough figures in starting at a+ 4% at 46 C upto a +18% at 70 C. And now she Purrs like a Kitten after hot soak, So thanks Cygnus1 for pointing me in the right direction. So as far as I can see the position of the IAT sensor makes little difference, as I would still have had to use the IAT correction setting/table. But why some people have this problem, and some don't is a different matter, Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted February 28, 2009 Share Posted February 28, 2009 Nice! I think IAT position is an over-discussed topic. Vapor lock is a much bigger factor in AFR's. Just make sure you are not running in warmup mode now when your car is already warmed up. Somehow...I ran into that problem when I tried to compensate for vapor lock on hot start via programming. It might have been just my typing error....but keep an eye peeled for it. Quote Link to comment Share on other sites More sharing options...
Zed2k Posted February 28, 2009 Share Posted February 28, 2009 Thanks yeah, I'm a bit worried about the onset of IAT correction as it seems to me that the sensor needs correction anywhere upwards of 40+ deg C. but most of the time in normal and fast driving the intercooler and water injection will keep the temps down way below that. I have an LED for warm up so can see when it's in warm up mode, Just as a side not I did bung a desk fan under the bonnet for 10mins blowing air over the fuel rail it cooled the rail down and also cooled everything else down by loads IAT temps went down to 31, so you can see why Nissan fitted this injector fan assembly to some 280zx and 300zxZ31 models. Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted March 18, 2009 Share Posted March 18, 2009 I had this problem today. After parking the car for about 15 minutes with the hood closed, I went out and measured the rail temp, the intake runner temps. Wow. The fuel rail was 130-140F and the intake runners were about 170-180F! I tried to start it but it took several tries. It finally started and barely idled at 18:1 AFR. It took about 5 minutes of rough idling and revving with the hood open to get the normal AFR's back. The IAT was reading reasonably low temps less than 1 minute after the restart. Note: my fuel rail is not a loop. If it were a loop, the hot fuel would flush out much more quickly. I glued a sheet of reflective-backed fiberglass to the aluminum fuel rail and wrapped some of the AN fittings in the fuel lines with the insulation. I will test again during the week. Quote Link to comment Share on other sites More sharing options...
SidWell Posted March 18, 2009 Share Posted March 18, 2009 Note: my fuel rail is not a loop. If it were a loop, the hot fuel would flush out much more quickly. So you are saying the pretty looking straight thru fuel rails are the source of the lean run issue? What would happen if the fuel pump was switched on for a minute prior to starting the car? Wouldn't all the hot fuel be returned to the fuel tank? Quote Link to comment Share on other sites More sharing options...
Zed2k Posted March 18, 2009 Share Posted March 18, 2009 I have moved the, IAT sensor back to the original position in the manifold, as it's tuned well in this position the sensor heats up rapidly in this position when idling, and temps are higher after hot soak about 70'c, the good news is the car still started well and was running a little richer than normal idle so I will have to back off the IAT correction a little, or it could choke itself in traffic. And now my LM-1 sensor is starting to play up shoing a free air reading every once in a while. bugger.. Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted March 18, 2009 Share Posted March 18, 2009 So you are saying the pretty looking straight thru fuel rails are the source of the lean run issue? What would happen if the fuel pump was switched on for a minute prior to starting the car? Wouldn't all the hot fuel be returned to the fuel tank? I imagine that a recirculating fuel rail would flush fairly well just from the fuel pump turning on with the ON key when MS first fires up. The injectors could still be in vapor lock. I can also try increasing the priming pulswidth at hot starts. I don't think the pretty fuel rails are any worse than the factory rails as far as vapor lock. Both rails have nearly the same problems. However, the factory rail is recirculated. This heats up the fuel in the tank during long drives though. Mounting the IAT sensor in the manifold will allow you to better tune for over-hot conditions. My IAT sensor is in the IC pipe before the TB. It doesn't get nearly as much heat soak there. Thus I can't use it to correct AFR's as much. The real solution is to insulate, recirculate, the fuel rail, and keep the engine bay temps down however you can. Quote Link to comment Share on other sites More sharing options...
Zed2k Posted March 18, 2009 Share Posted March 18, 2009 Very true, I have a return from the fuel rail back to the surge tank, when i took the car out in very hot weather last year the bosch 044 motorsport pump started making alot of noise, and I found that the fuel was heating up partly from the front and partly from my off side rear tyre as the surge tank is mounted against the tank by the wheel, I think I need to fit a sheild just to deflect the tyres heat from the tank. this only happend once when it was 37 degrees C. I will kepp you updated and see how the engine runs once the summer gets here. Quote Link to comment Share on other sites More sharing options...
Derek Posted March 19, 2009 Share Posted March 19, 2009 when I was building my surge tank setup I wondered why everyone dumped the hot return fuel into the surge tank and then back into the main tank. I have mine run that way for now but I plan on re-plumbing it soon now that it's getting hotter out. Derek Quote Link to comment Share on other sites More sharing options...
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