94 bronco, 5.8L, E40D. Have replaced the EEC, MAP, IAC, TPS, ECT, O2, ACT, TFI module, Distributor, cap, rotor, wires, plugs , and filters. All within the past year. I am still getting this particular problem and am at a loss. Had a major electrical surge that fried eveything. The truck will be running fine, then the idle drops and bounces from dead to 1000rpm a few times, then everything is fine again. It will do this 5or 6 times in a 45 mile drive. Doesn't matter what the weather conditions or outside temp. I am not getting any codes, KOEO or KOER. I have rebuilt the engine 30K ago. It also has a 5.0HO cam advanced 2* with a FRPP 9 keyway, could this be my problem? I was running at 16*BTDC and bumped it back down to 10*BTDC and the problem is unchanged. I am gogin to check vacuum lines today. The truck has 195K on the ticker. Any thoughts or ideas would be greatly appreciated.
Tim

 

that cam is more then likely your problem. your bronco is speed density so cam selection is very important and must have a lobe seperation no less then 114*. do you have all the specs on that cam. maybe with the cam set strait up may work better but lob sep is important here.

 

I want to say the LSA was 117*. I know most of the Lightning guys run this cam SD and have no problems, but the strategy in the ecm's might be different enough to make it not work. I can post the specs on the cam later today, it is a 5.0 HO cam out of a 93 Stang GT. I am running the F4TE roller block with roller valvetrain also.

 

Here are the cam specs off of the cam card.
INTAKE AND EXHAUST LOBE SEPARATION ANGLE: 115.8 degrees
VALVE OVERLAP AT .050= -19.3 CRANK DEGREES

INTAKE:
valve opening: -9.6BTDC
Lobe centerline 115 degrees(ground with .8 degrees advance)
valve closure: 40.7 degrees ABDC
duration: 211 crank degrees
lobe lift .2774"
Valve lift (1.6 rocker)= .44384"
Lobe area= 21.36" degree

EXHAUST:
valve opening: 42.3 bbdc
lobe center: 116.6
valve closure:-9.6degrees
duration: 212.7 degrees crank degrees
lobe lift: .27736"
Valve lift: .44378"
lobe area= 21.45 in degree"

 

so maybe having it advanced those 2* is causing some issue? was it a used cam or a new one? have you double checked your firing order?

 

It was a used cam, I removed it. Only had 29K on it. Had it read and everything checked out ok. The firing order is correct, just checked it last weekend. Everthing was running fine when I had the Lightning intake and ECM installed with this cam as it sits right now. I am leaning towards a drop in the voltage that is causeing the fuel pump to surge, or a vacuum leak at the FPR. Does this sound right? Or maybe one of the vacuum solenoids is bad, I know they are not controlled by the ecm, so they wouldn't trip a code. I have noticed that it does it more when I am at part throttle, say 2000 rpm and take my foot off of the accelerator the rpms drop to almost nothing 100rpm or less.

 

yes check fuel pressure at the rail. also pull vac line off FPR if gas is present figure its bad . do you hear the pumps turn on with the key on?

 

Pump comes on with the key. FPR has no fuel in it, but It was replaced due to fuel in the FPR 6 months ago. Fuel pressure, I cant check it at the moment , no gauge, but I will have to check it. The reason I was thinking along low voltage, is the alternator has been fluctuating here recently, you can see the voltage on the gauge move up and down, I know a little is ok, but this drops down really low. It is the only part of the electrical system that wasn't replaced, but it checked fine at the time, but could be failing now. Thanks for the help and ideas, I will continue to plug away at it. Keep the ideas coming, please.

 

This problem started when? When the new rebult motor or that cam was put in?

 

Prior to both, I have been batteling this problem since I bought the truck 3 yrs ago. When I reset the computer it continues to do it even during the learning cycle. The problem has only gotten worse since purchase. It didn't do it as bad, when it had the Lightning setup on it, but it still did it.

 

Check you grounds, check all connectors for corrosion, check the positive power wires to the computer. Perform an eec wiggle test first if you want.