Maybe TPS problems?

[dmontoya]

Hey all I am new to Bronco Zone. Just bought an '88 with a 351w 5.8L. Not sure of the tranny. I have a check engine light on, and well so far I've had up and down idle issues, to sluggish engine. I would start engine from cold, it would run at 1200-1300rpms then after 2 min or so choke turned off and engine would go into frenzy 600-1000 rpms constantly. With new IAC valve it corrected the up and downs for a little bit, and check engine light would sometimes disappear, but still came on, and engine still seemed hesitant when it was time to get up and go (highway on ramps) so I replaced both bypass and exaust bypass diverter valves. The small plastic vacuum hose on the air control valve broke from brittleness, so I elec. taped them back together. Then I started reading these forums and found out it might be a TPS sensor. Why not try it. So I did as Haynes manual said to. Now that I have the new TPS on the same as the old one was with the wires coming out of TPS facing the battery. Well my voltage was 1.25 at closed throttle (lowest I could get it, without blocking threads) and 4.80 at full open throttle. Did I do something wrong, because now after replacing the TPS my engine is REAL sluggish is hesitates to go, and now if I floor it while going 30mph she wont get up to move she practically dies. What gives?

 

[Seabronc]

I'd go back and check for vacuum leaks. I would replace that broken line putting tape on it, even if it works now, will fail. If it is the small plastic tubing, you can patch it by using a piece of rubber vacuum hose and sliding the plastic hose inside from either end to make the connection. Off the top of my head, I believe the size to use is 1/8 inch.

An easy way to find a vacuum leak is to use a propane torch, (unlit of course). Open the valve and move it around the engine. If you get a change ion the engine speed, you have found a leak.

Just to be on the safe side have a fire extinguisher near by, low risk but still a spark of some sort could set it off.

Good luck,

>-

 

[dmontoya]

An easy way to find a vacuum leak is to use a propane torch, (unlit of course). Open the valve and move it around the engine. If you get a change ion the engine speed, you have found a leak.

Just to be on the safe side have a fire extinguisher near by, low risk but still a spark of some sort could set it off.

Good luck,

>-

So run the propane along the top of engine, the vacuum will **** in the propane causing a change in idle speed, thus telling me where the leak is? ok, when I get closer to the leak will the change in idle be dramatic? If so, will the engine rev high or choke out? Another question. I have the 351w EFI 5.8 1988. My throttle body connects to the aluminum intake on top of manifold. Just under this on the passenger side valve cover is a tube sticking out (looks like a vac line) what should it connect to?

 

[BroncoJoe19]

So run the propane along the top of engine, the vacuum will **** in the propane causing a change in idle speed, thus telling me where the leak is? ok, when I get closer to the leak will the change in idle be dramatic? If so, will the engine rev high or choke out? Another question. I have the 351w EFI 5.8 1988. My throttle body connects to the aluminum intake on top of manifold. Just under this on the passenger side valve cover is a tube sticking out (looks like a vac line) what should it connect to?

I don't know how dramatic the change will be, but it wil increase idle speed.

I wish I had my bronco here to look at for you, but that sounds like it is the cause of your idle problems... a major vacuum leak.

You should have a vacuum diagram on your radiator support, or up under the hod. That may be helpful (if it is still there).

 

[BroncoJoe19]

Please read this... the IAC may cause your problems.

http://www.fordfuelinjection.com/?p=39

Checking for vacuum leaks.

Some of the sensors and some of the actuators either read the amount of vacuum, or use vacuum to move controls, therefore it is important to the proper functioning of the engine that your vacuum system is fully intact. Otherwise one may get codes falsely indicating that there is a problem with a controller/actuator, or a sensor when in reality it is caused by a lack of vacuum.

Look at your rubber vacuum hoses (they are about 1/4 - 3/8 inches in diameter, if they are dry rotted or cracked, replace them. IF they slip on/off of their connectors too easily, they may have stretched out a little bit, cut the ends off, and put them back on.

You may listen for a leak. Sometimes using a cut off piece of garden hose is a good aid to listen with. Sometimes a cardboard tube (like from gift wrapping paper) is helpful. Just remember that whenever you stick your head inside a running engine compartment, that you are not wearing any loose clothing or jewelry that can get caught.

Another suggestion is to use a spray can of carb cleaner and spray around the bottom of the intake manifold, and the base of the throttle body assembly. IF there is a leak, you should hear a change in your engine.

Keep a fire extinguisher handy, or use water instead of carb cleaner (it works, but not as well.) Be aware that if you use water and the wires get wet and it runs worse... your wires may be bad, and the water is allowing them to arc instead of jump the gap of the spark plug.

Another suggestion is: to take a propane torch, turn it on (but don't light it) and move it over the vacuum hoses and connections. The engine RPM's will increase if there is a leak and the propane gets sucked in.

From another friend.... Don't forget to remind folks to check the PCV valve, hose and grommet !