TBIThrottle Body Injection discussion and questions. L03/CFI tech and other performance enhancements.
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Car has always cranked quite a bit before firing up. After sometuning the problem wasnt any worse but its not any better either. I am pretty confident i haven't touched the value that has to do with this in tunerpro at all. I remember someone mentioning something about fixing this problem while tuning their setup but i cant find it anywhere. Any suggestions? '92 tbi by the way
__________________ Don @ DiabloSport
'92 RS /// TBI 305 - H/C/I, full exhaust, 1.5 roller tip rockers, tune
'94 Mustang GT - Vortech, full exhaust, h/c/i, gears, power pipe etc..
This can be caused by a bad ECM (ECM isn't turning on the relay) or bad fuel pump relay. At key-on, engine-off the fuel pump should run for 2 seconds. If not then long crank times will occur.
The engine will need to be cranked until some oil pressure builds. This closes the oil pressure switch for the fuel pump relay bypass and turns on the pump.
This can be caused by a bad ECM (ECM isn't turning on the relay) or bad fuel pump relay. At key-on, engine-off the fuel pump should run for 2 seconds. If not then long crank times will occur.
The engine will need to be cranked until some oil pressure builds. This closes the oil pressure switch for the fuel pump relay bypass and turns on the pump.
RBob.
I must chip in here because on my 88 tbi i can hear my fuel pump run for the 2 seconds after i turn my key on, then i crank it over and it cranks for at least 4-5 seconds before it starts, but my vavle seals r bad so maybe it takes awhile for the oil to clear off the cylinders walls and spark plugs causing my long crank???? Sorry to hack the thread but i also have this same problem. Could bad valve seals be offsetting my oil pressure?
Well that doesn't help then. One thing that I need to mention is that 'long crank' times are relative. Long crank to one person is a not so long crank to another.
However, there are some other items that can contribute to long cranking. One is that it is inherent to how TBI works. At key off the manifold is run dry. At key-on you can't pump the throttle like a carb to add fuel. It takes some cranking to get fuel in the manifold.
Low fuel pressure and/or an incorrect CTS reading can make this worse.
What I usually do is to key-on, pause, crank briefly and pause. The crank to start. The brief crank puts some fuel in the manifold which needs to evaporate before it is of any use.
I've played with having AE active during engine not running (treat it like a carb with key-on, pump the the throttle). Along with a fuel pulse at key-on. Both allow instant start up. However, both can also cause flooding, so I didn't go with those functions.
Check the fuel pressure. Nine psi is minimal. Then see if the CTS is reading a tad high. Otherwise it just may be the nature of the beast.
With the older ECMs, I had the same issue. It took about 6 seconds or so for the manifold to prime enough to get fuel into the cylinders. The ability for the computer to prime on cranking didnt come until the later PCMs. Those add a large shot of fuel for the first few DRPs for when you first start cranking to prime the manifold.
With the older ECMs, I had the same issue. It took about 6 seconds or so for the manifold to prime enough to get fuel into the cylinders. The ability for the computer to prime on cranking didnt come until the later PCMs. Those add a large shot of fuel for the first few DRPs for when you first start cranking to prime the manifold.
Yep, PCM definately fires right up, even when its 20*F outside.
This can be caused by a bad ECM (ECM isn't turning on the relay) or bad fuel pump relay. At key-on, engine-off the fuel pump should run for 2 seconds. If not then long crank times will occur.
The engine will need to be cranked until some oil pressure builds. This closes the oil pressure switch for the fuel pump relay bypass and turns on the pump.
RBob.
Doesnt the oil pressure switch also run through the relay? SO I'd assume the relay is good?
Doesnt the oil pressure switch also run through the relay? SO I'd assume the relay is good?
The oil pressure switch and fuel pump relay are in parallel to each other. So either one individually will turn on the fuel pump. The ECM will turn on the relay for 2 seconds at key-on. Then whenever it sees pulses from the distributor (engine is running or cranking).
The oil pressure switch will turn on the fuel pump whenever the pressure is above 4 psi (or so). This can actually be checked on a cold engine. Start it, let it run for a few seconds, then key-off. The fuel pump can run for several seconds until the oil pressure drops (cold oil).
Rbob yea i would its about..idk..5 seconds of cranking before she fires. I also notice that sometimes it even happens when the car is restarted after driving, but in most cases she fires right up. As far as fuel pressure goes its 13psi.
From a tuning standpoint, the '8746 has a Cranking AFR vs Coolant table. This table defines the AFR while cranking. There is also a cold cranking multiplier for this value. This table has a coolant threshold before it takes affect. Then the multiplier is based on engine vacuum. In ANLU the CTS needs to be below 14F for the table to be used.
Once the cranking AFR is created, the code will use either that value or the open loop AFR, whichever is richer.
I think for the Crank AFR multiplier vs Vac table, the first row is 80 KPa and the last 0 KPa.
It works by multiplying the AFR from the crank table by the value in the multiplier table, then dividing by 16. I haven't tested this portion on the bench, but it looks to be that at initial crank it is richer, then leans as the engine vacuum increases.
May be able to set up the calibration for an very rich inital crank AFR, then have is taper off to prevent flooding.
Probably not the problem, but I would usually have to give a 1-2 second crank for starting. I had a bad ignition control module in the Low RPM. Replaced it and car fired up and was running before I could let go of the key, even after sitting for a month. It's worth a check at least.
good call, i will take a look at that, i am pretty sure the original one is on there. and Rbob that table looks like it may be the answer if its even a problem
