4.9 stroker done....now computer gremlins

[bradcarrier]

Got my stroker back from Keith @ newcomerracing(newcomerracing.com), great guy.....built an awesome motor, made 326 hp/322tq on the dyno(with carb) with stock head. Hear are the specs....4.9 stroker, custom ross pistons, hd 4.2 crank, custom bushed rods, custom comp cam 230/236 108 lobe seperation, comp lifters/springs,10.5/1 compression, redlines 6,000, stainless 2.02/1.60 valves, MLS head gasket. I was there for the dyno, ran great, idled great

So put it in my 95 wrangler OBD1, also installed wide band 02 and aeromotive fp regulator,ford 24 # injectors, cobra fuel pump. Runs great above 1500 rpm(most of the time). Idle is another story, does not want to idle for shit, cuts off, sputters. Also jeep sometimes will randomly start running on 4 or 5 cylinders. If it starts skipping and you go plug and unplug the injectors it will start hitting on all 6. So I figured injectors were bad, replaced them with some more 24# fords, same shit randomly missfires for a while, cold or hot no difference. Now I did put some accell 30#'s in there and itstill idled like shit and afr's were to rich, but the random misfires seemed to stop. I have replaced all the sensors, 02,map, dist pick up, cut the ears of the distributer and got it right. Not sure if I need a custom tune for the 1500rpm and below issue...any thoughts or ideas. Fuel pressure with the 24# injectors right now is 45psi, got no better when I varied the pressure between 40-50 psi. A/F ration at wide open throttle varies from 11.5-12.5.

[dwg86]

What is your vacuum at idle? I'm assuming the duration you posted is @ .050? With that kind of duration and a 108 centerline I'm betting your computer doesn't like the low vacuum. I have a 401 in my jeep cj5 with 228/232 duration @ .050 110 centerline, 10.5 compression, and it will shake your filling out.

[bradcarrier]

What is your vacuum at idle? I'm assuming the duration you posted is @ .050? With that kind of duration and a 108 centerline I'm betting your computer doesn't like the low vacuum. I have a 401 in my jeep cj5 with 228/232 duration @ .050 110 centerline, 10.5 compression, and it will shake your filling out.

not sure on the duration I will have to ask, I'm thinking the low vacuum is freaking the map sensor out?

[jsawduste]

What is your vacuum at idle? I'm assuming the duration you posted is @ .050? With that kind of duration and a 108 centerline I'm betting your computer doesn't like the low vacuum. I have a 401 in my jeep cj5 with 228/232 duration @ .050 110 centerline, 10.5 compression, and it will shake your filling out.

not sure on the duration I will have to ask, I'm thinking the low vacuum is freaking the map sensor out?

108 centers is a bit narrow for decent idle vacuum. 133/114 is a much better bet.

[Cheromaniac]

What is your vacuum at idle? I'm assuming the duration you posted is @ .050? With that kind of duration and a 108 lobe separation I'm betting your computer doesn't like the low vacuum.

I think you've hit the nail on the head. It's not just the narrow LSA that's the problem. When you combine it with the long opening duration, there's simply too much valve overlap. The resulting low idle vacuum causes the engine to run excessively rich and that's the Achilles heel of the MAP sensor-based speed density EFI system.

[lafrad]

its *definately* low vacuum issues.

Grab a map adjuster like: http://www.splitsec.com/products/psc1/PSC1003.htm
and pull out 35-40% fuel in the idle area and idle rpm.


if you have an OBD logger and some patience, you can do a full fueling tune with that map adjuster. you want your fuel trims to be as close to 0% as possible, across the board.

[lafrad]

Do you remember the idle speed on the dyno? Big cam setups SOUND like they idle great at 1200 rpm. they may sound like the idle "well" at 900 rpm. they may not idle at all under 750 rpm. The stock ECU targets idle speeds below 750 rpm all the time.

[bradcarrier]

Actually was idling about 750-800 on dyno, unpluged my map and it idled very good around 950. Reason being I had drilled a small hole in the throttle bottle blade to compensate for it not idling correctly with the map plugged in. I have a new blade to install. Need to know what the voltage is for the TPS at idle is supposed to be. Also need to know if having an adjustable MAP sensor is gonna due the trick or am I going to have to figure out another way to get the map sensor some vaccum at idle.

Anybody tried one of the stand alone throttle body style fuel injection systems on a clifford intake(might go this route if I cant resolve this issue) Thanks in advance

[CobraMarty]

Change the cam or pull the EFI off and put on the carb and carb intake manifold.

[lafrad]

the map sensor *NEEDS* to see the actual intake vacuum. thats the only way it can even come close to figuring out how much fuel should be in the engine. no use trying to "find" vacuum.

If you are not wanting to swap to a cam with a bit more vacuum, yank the stock ECU and go aftermarket. Or just go back to the carb.

[bradcarrier]

So basically no way to run what I got with stock efi, I race the jeep offroad in the ECORS series. Anybody had any experirences with a good reliable carb in off road situations(jumps hill climbs, rockcrawling, etc.) Also has anyone tried the standalone tbi fuel injection systems that just use a wideband to tune?

[wjtom]

the cam has to go.why he ran a 108 lobe seperation in a fuel injected car makes no sense. from what i was always told usually that is for cars with open exhaust.just doesnt work well with an exhaust system.plus look at any streetable fuel injected cam and they usually have 112 plus lobe seperation.all you did was give up drivability to gain some peak torque in a narrower rpm range plus gain a bunch of problems.i have a525 lift 218 228 duration cam on 110 which thanks to 505 should have been 112 or 114 which works fine with the stock ecm.little lumpy but not bad still idle at 650.i would have chose a little more duration and wider lobe seperation if i had a say in it.

[racing89]

Change the cam. ANY cam choice better than an antique carb setup.

[superstingray77]

Chris at Performance Injection Hardware can likely help sort you out.
He built a nice program thus far for my OBD2 WJ with a large solid cam in it, Open loop is the only way to get a cam with that much overlap to work. Try adjusting the MAP voltage down to 4.25 this will likely get the idle and part throttle to be drivable but then you will have to find a way to program the timing/fuel in the midrange/WOT back into it.

[email protected]

[lafrad]

A Standalone EFI system will get this cam to run. Its not that big of a deal, you just have no control over idle setpoint, spark, or fueling on the standard OBD1 jeep ECU.

http://www.painlessperformance.com/webc ... x4+OffRoad

Painless makes an aftermarket EFI setup for the Jeep 4.0 (and strokers)

I bet an install of that, a little bit of work with the tune, and you'll have a smooth running 4.9L with 800-900 idle.