ok i know i'm not the only one who has problems starting the car perfectly. it starts, but after some cranking. i actually got a datalog of it, and when it starts to go (above 300 rpm) my spark angle drops from 10 to 6 for some reason. that i think may be my problem. is that supposed to happen, or does anyone know why it might?
skip the megasquirt questions, we ran into this same issue...
First off, are you running a return system with a fuel pump controlled by the megasquirt? or are you using the returnless system controlled by the factory PCM.
We noticed that when using the factory computer to control the fuel system, when cranking the fuel pressure will NOT build until you've been cranking the starter for 2 full seconds, which is a long time. Until we put a 5v on the crank position sensor, this was an issue for us.
i dont start my car until i hold the key to on for the fuel pressure to build up anyway, so that shouldnt be a problem. all my spark settings for cranking and for idle and stuff are at 10, any ideas?
i dont start my car until i hold the key to on for the fuel pressure to build up anyway, so that shouldnt be a problem. all my spark settings for cranking and for idle and stuff are at 10, any ideas?
Don't dismiss my suggestions so fast, I've already been through this problem...
are you running a fuel pressure gauge? the pump runs for 2 seconds at startup, but if you read the shop manual on the car it tells you that the system is running a test at startup - it didn't come near full pressure during the 2-second pulse with key on. Also, this system does NOT have a check valve - pressure is NOT maintained when the pump is not running.
Here's a basic Megasquirt rule of thumb: if changing the settings doesn't fix the problem, then it's not a problem that you can tune out...
Hook up a pressure gauge, watch what it does at startup, you'll see what I am talking about. Then unhook your tach signal from the CKP wire, crank the engine again and see what happens. Also, you probably have a CKP error code... we did - and when the code's gone, the problem disappears.
Also, the problem is NOT timing related. Any car will start on 0 degrees of timing, in fact that's what HEI modules, EDIS modules, etc do during cranking. Definitley not an ignition problem if the car starts and idles eventually...
Give it a try and please post up your results, I don't mean to sound like a dick about your issue but I am quite sure your startup problem isn't ignition related.
-scott
Last edited by dieselgeek : 06-26-2007 at 09:04 PM.
i dont start my car until i hold the key to on for the fuel pressure to build up anyway, so that shouldnt be a problem. all my spark settings for cranking and for idle and stuff are at 10, any ideas?
Don't dismiss my suggestions so fast, I've already been through this problem...
are you running a fuel pressure gauge? the pump runs for 2 seconds at startup, but if you read the shop manual on the car it tells you that the system is running a test at startup - it didn't come near full pressure during the 2-second pulse with key on. Also, this system does NOT have a check valve - pressure is NOT maintained when the pump is not running.
Here's a basic Megasquirt rule of thumb: if changing the settings doesn't fix the problem, then it's not a problem that you can tune out...
Hook up a pressure gauge, watch what it does at startup, you'll see what I am talking about. Then unhook your tach signal from the CKP wire, crank the engine again and see what happens. Also, you probably have a CKP error code... we did - and when the code's gone, the problem disappears.
Also, the problem is NOT timing related. Any car will start on 0 degrees of timing, in fact that's what HEI modules, EDIS modules, etc do during cranking. Definitley not an ignition problem if the car starts and idles eventually...
Give it a try and please post up your results, I don't mean to sound like a dick about your issue but I am quite sure your startup problem isn't ignition related.
-scott
dont worry, i dont think you are a dick, any help is appreciated. im just too lazy to hook up my fuel pressure guage haha so i want it to be my last resort.
when you said i should be throwing a code do you mean now or if i would unplug the ckp wire from the pcm?
we had the same deal where it cranks and then slowly comes to life. Which pisses me off because an EFI car should start NOW.
We tried EVERYTHING. Then I realized we had no fuel pressure gauge... we rigged one up and saw that it only makes a few PSI at key on; then dies off immediately! then you crank the starter, and it takes 2+ seconds to build pressure again.
We also noticed it was tied to a CKP error code. Adding the pullup resistor to the crank position sensor made this all go away... we used a 1k resistor and 5v added to the CKP signal.
However, when dyno tuning we decided to go with a return fuel system and pump driven by the MS. Because with this guy's hahn 20g kit, the fuel pump pressure clearly had a problem keeping up at 20psi of boost... it has a lag effect...
I can share the tune we came up with too, if anyone wants it. The writeup is taking longer than I had hoped because we had all knids of "unscheduled meeting" BS at work today. I am almost finished.
i dont have a code right now, does that change anything?
I'm not sure, but I think the best thing to do would be to rig up a fuel pressure gauge temporarily (don't need anything fancy)
here's what you should check during cranking just to cover all the bases:
(1) do you have RPM signal in Megatune as soon as you crank the starter?
(2) Do you have battery voltage at each injector as soon as you crank the starter?
(3) Do you have consistent fuel pressure when you crank the starter?
On our car, the war (160 degree) cranking pulsewidth with 65 lb injectors was 3.7ms. If you have smaller injectors, this will go up to 4+ ms.
im actually retuning my cranking pw because i changed it fro mat/clt average to just clt temp im hoping thats teh problem actually, but im just looking at all angles. i also put it to priming pulse twice because i figured a priming pulse would be a sort of kick in the pants to get it started so i figured 2 is better, do you think i should go back to one?
im actually retuning my cranking pw because i changed it fro mat/clt average to just clt temp im hoping thats teh problem actually, but im just looking at all angles. i also put it to priming pulse twice because i figured a priming pulse would be a sort of kick in the pants to get it started so i figured 2 is better, do you think i should go back to one?
the engine should at least start warm, with NO prime pulse. I'd disable that, and TPS enrichments, O2 corrections, etc. until you figure out what pulsewidth is likes best.
what size injectors are you running? you sohuld be somewhere between 3.5 and 5.5ms for the 160-degree warm start. Just use the regular CLT enrichments, and don't mess with anything else until you figure out what pulsewidth cranks best. I'm still pretty sure you don't have a problem with cranking pulsewidths though, our car would start on a wide range of pulsewidths just fine, after we figured out that the long cranking period was based on fuel pressure. speaking of which, did you check that yet?
The 1st gen ecu turns on the fuel pump for 2 secs after key-on. Does the NGC not do this?
It does, but on our car it only came up to 25ish psi and dropped off quickly. I think it dropped off because either the Walbro fuel pump he used, which
came with his turbo system, doesn't have a check valve perhaps?
When we didn't have a CKP error code, the fuel pressure would come up as soon as the starter cranked. One behavior I noticed, was that the dash tachometer would always "wittle" right before the engine would catch, when the cranking pulsewidth was tuned well. So, I instructed the owner to watch the tach if it was cranking too long, he reports that when the tach starts showing rpm (very low) during cranking, car always starts right up.
Speaking of which, he called me to say that after a few drives, he got a new error code about the CKP (different one than what we'd seen before, a "sync error?") and the car was taking a long time to start yet, and with the same tach behavior... I think maybe our 5v pullup on the tach input isn't quite right... we'll work on it and see what we can figure out,
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