I rebuilt my injectors, changed almost all sensors (cleaned IAC), tb, etc, fluids, plugs, coil, etc. I've done quite a bit to it. Cleaned the upper intake.. the only thing not new or extensively cleaned are the plug wires, distributor body and fuel pump/filter.

The symptoms I have.. after warmup, the idle is a bit rough. Not terrible, just not clean or 'even'. Feels like it has the occasional miss or low power fire with no discernable pattern.

It doesn't fire up instantly, I have to crank for a second warm or cold. Thought the rebuilt injectors would fix this (the internal filters were filthy), it made it better, but didn't fix it. I can't find any fuel leaks.

My engine is just flat out noisy, noisier than the 400 in my 78 f150 or the 302 in the 1980 Bronco.

Are these symtoms just the nature of my Bronco? for a motor with 120k miles? big v8? etc? I don't know how these Broncos ran new, I keep chasing that clean idle withouot feeling the motor at all; like I have in my 78 F150, but both this 351w and 302 don't have that same steady idle and you can feel the motor running while in the vehicle, my 400 also burned oil, so I dunno what the deal is.

I'm also getting a hum from somewhere if I hit the gas and let off, I'm suspecting fuel pump. Would my fuel pump cause any, if not all of these issues?

Throwing no codes except an occasional EGR out of range memory, and that's only if I drive for an extended period at highway speeds.

 

I don't have many ideas for you right now (replace the spark-plug wires?, check the spark-plugs? coil?), but i have to say my 302 iddles perfectly, not like when it was brand new, but it does very well.

 

Your EGR out of range is a significant code from a performance aspect. Erratic EGR codes could indicate poor vacuum supply, a cruddy EGR valve (yes they can be cleaned...carefully), or even a faulty EVP sensor (tells the computer the EGR valve position). Keep in mind that the EGR system changes the contents of the air and gasses moving through the combustion cycle which is essentially changing your fuel-air mixture beyond a point where the on-board computer can make corrections.

 

supply to EGR only, right? If I had poor vacuum I'd think i'd be throwing other codes. Then again, this 90s is pretty basic, I have to all but purposely break something for it to throw any codes.

You think changing the EGR valve might help? It was 33 if I recall correctly, the EVP?

 

Since the EGR vacuum supply is controlled by the TAB and TAD solenoids you may or may not have other issues with a broken EGR vacuum supply line. The line is a GREEN plastic line that comes around the back side of the engine to the EGR valve. Code 33 indicates that the computer did not detect the EGR valve opening during the self-test. If you have or can get access to a vacuum pump, you can test to make certain the EGR valve is holding vacuum. Simply apply vacuum to the valve and as long as the vacuum applied doesn't drop, the valve is fine. If the valve tests good, and the vacuum supply line is functioning (vacuum supply must provide at least 1.5 inches of mercury to activate the EGR valve) then the EVP sensor is the problem and should be replaced.

Hope this helps.

 

it helps a great deal, as I just assumed it was thrown from different driving conditions, since it's during a self test I know the problem is always there. I've already replaced vacuum lines, so I know that isn't the issue, I'll put a pump on it and see if it's the valve or the sensor.

You don't have a diagram for the lines for EGR, do you? I might have run the vacuum lines to the wrong spots, I doubt it, but it's worth checking.. I thought EGR would have run off of straight vacuum.

 

Should it be getting vacuum all the time? I'm getting 0hg from the vacuum line. EGR holds vacuum fine.

 

ugh, only showing 14hg vacuum at intake, I need to check timing.

 

Unfortunately, I don't have a full vacuum diagram for the EGR and Thermactor system. Maybe that should be my next project to help folks around here. Shouldn't be too difficult to draw one up that makes heads or tails out of the components. I'm not aware of one that covers more than the under-hood decal shows on these trucks. Hmmm, gots me an idear!

EGR should only operate in "closed loop" operation. The rest of the time the computer needs more accurate control over fuel/air mixture than it can handle with EGR thrown into it.

 

I just adjusted my timing, the best I can get is 15hg. if i'm sure I don't have any leaks, I'm pretty much left with the fact that I have a worn motor, aren't I?

Later I'll unplug all vacuum and see if I can get the readings up, I've not checked my booster (my brakes feel fine), cruise control (works fine), etc.. I just thought 351w's were dogs, this one is, especially compared to the underrated 400 in my F150.

 

15hg should be plenty of vacuum, the EGR only needs about 1.5 to activate it. On a good day my stock 302 only does about 12-13.

 

I'm still not convinced it's the EGR causing my motor to run rough.. if at idle EGR isn't being used (no vacuum) it should have no effect on the motor. I'll change the sensor anyways, but I'm going to keep looking elsewhere to narrow down the issue I'm having.

Someone had messed with the idle screw, so I messed with it again. Brought the screw in (increase idle), advanced timing a tad and now it idles more smoothly, still not great though. Funny that my gear-idle didn't increase, just smoothed out at 750. In park it sits around 900 now instead of the 750 like before. Suspected idle mixture because of the surging, having to tap the gas in park for it to go to a normal idle, etc, it just feels like the computer is compensating for poor fuel/air.

Is there any reason for why my front two fuel injectors would be much louder than the rest? there's also little change in the way the engine runs when I unplug the front-driver's side injector, though there is change.

 

That is NOT an idle adjustment! ...and to get it back where it belongs is a tedious process. That's why it won't idle right. There is NO adjustment for the idle... it is completely controlled by the computer. That screw is a throttle plate stop nothing more. It keeps the throttle plates from sticking in the bores. (Ford should have cut that bolt head off once the silly thing was set, in my opinion). It only needs to be factory set then left alone because adjusting it wreaks havoc on the entire engine control system. The only reason it is there at all is because the adjustment is slightly different from throttle body to throttle body. The computer isn't even trying to control idle mixture because the throttle is slightly engaged... this sends TPS readings at idle other than 0 VDC and more air than is calculated for is entering the engine during what should be idle. If the stop screw is run in enough, the computer WON'T let the truck idle properly because there is TPS voltage indicating "tip in" accelerator input which negates the entire idle control process from the computer.

 

It runs rough at power as well, not just idle.

Anyways, when I bought it the Bronco had a bad TPS and an intake leak. The guy I got it from adjusted the stop screw, when that didn't lower the idle he bent the throttle stop tab outwards.

I tried unplugging the iac and adjusting the screw while in park until it sounded like it was right about to kill the engine, then plugged in the IAC, I was told this is how you do it, that's how it was set before I started this thread.

After adjusting it my way, which was just turning it inwards until I was happy with the idle, it idles much more smoothly. 750, fluctuates maybe 10-20rpm in drive, 900 RPM with the occasional low power fire in park, more fluctuating in park than drive.

While the screw is inwards a bit, the stopping tab is bent outwards, so I think it is close to factory. Unplugging the IAC still affects the idle, so I'm sure it and the TPS are controlling throttle at its current setting.

I get that low power fire at any RPM as far as I can tell. I'm going to look into the O2 sensor, the engine has at least 130,000miles on it and I doubt it has ever been changed. The extremely loud front injectors makes me think they're running a bit on the lean side, and they're loud at idle and increase speed at higher RPMs. They all click, but the front ones sound like lifter tap and you can hear them pretty well from inside the cab and outside the truck.

An old o2 sensor would cause many of my issues if I'm not mistaken? Even if not, I'm sure it wouldn't hurt to change a 20 year old o2 sensor with 130,000miles on it.

 

You siad you had noise from the fuel pump. How is your fuel pressure? Have you changed fuel filter?