rev bogging down..vacuum problem?

[89frankenford]

ok guess this is a seprate problem from the misfire problem i have and am trying to track down


aside from the misfire (i have that in the other thread i made and am currently tracing down the problem. i have a major hesitation when i am at idle then hit the accelerator. basically it goes from 22 In/Hg in vacuum down to 0 In/HG then back up to 22 and it will rev. but it drops to 0...im assuming this is NOT normal. now with that said i have tested all the vacuum lines and none of them have holes and they all hold 22 In/HG of vacuum. i do have a new vacuum reservoir installed and that didnt help....is there something im missing??



here s the other thread with my other problems im trying to solve
http://www.fordtruckfanatics.com/forum/showthread.php?t=14484

 

[Skandocious]

If I'm understanding correctly-- you're concerned that the vacuum drops to zero when you rev it? It is normal behavior to have your highest vacuum at idle and your lowest vacuum at WOT. Think about it-- at WOT your throttle plates are wide open so the engine can't take in air fast enough to create a vacuum inside the intake manifold.

 

[89frankenford]

that i understand but do you hear the motor when i rev it? it stops then revs up. the throttle response is crap IMHO. im not sure if thats just normal or is there something wrong?? thanks for the help

 

[NeXtras]

i dont know much about the 300 I6, but mine had the same issue last night, turns out the plug i put on the PCV vac port on the INTAKE blew off.. made it idle rough too

 

[Raptor22]

I know mine doesnt do that. Mine is very smooth, and well normal. You have something going on....

 

[john112deere]

Mine's got a flat spot like that, too, but kinda intermittent.

Makes it look like I can't drive a stick....

I've always assumed it was a sensor issue- TPS, maybe- but basic diagnostics didn't come up with anything bad so I just live with it.

 

[Skandocious]

Turns out the plug i put on the PCV vac port on the INTAKE blew off.. made it idle rough too

Gee, imagine that

 

[d-kuzmen]

How does it go when driving? DO you loose power or bog down?

 

[89frankenford]

How does it go when driving? DO you loose power or bog down?

well basically i guess it loses all power. it goes from running then drops right down and then it revs. here is a pic of what im trying to explain

 

[Old_Paint]

This is on an '89 six lunger SD system, right?

Check real close for the smallest of intake leaks or perhaps in the line from the manifold to the MAP sensor.

The type of flat spot you're describing is similar to when the accelerator pump quits on a a carbed engine. I would expect a similar response if the MAP isn't getting or sending the appropriate signal for actual vacuum condition to the ECM, and it's failing to enrich the A/F mixture quick enough.

Timing can also cause this problem. Make sure the SPOUT connector is tight, and that the timing jumps advance when you hit the throttle. If there's a delay in the timing advance, or it isn't advancing, then it will have a pretty nasty flat spot too.

Timing won't throw any codes in the ECM. The only signal from the ignition the ECM will flag is the absence of PIP. It does not check to see if the ignition actually advances the timing when told to. If the MAP sensor is "good", it won't set a code either. But, it's a pretty broad spectrum for a MAP sensor to check good on the ECM, but it may not be up to par any more. It IS 20 years old, after all.

 

[89frankenford]

This is on an '89 six lunger SD system, right?

Check real close for the smallest of intake leaks or perhaps in the line from the manifold to the MAP sensor.

The type of flat spot you're describing is similar to when the accelerator pump quits on a a carbed engine. I would expect a similar response if the MAP isn't getting or sending the appropriate signal for actual vacuum condition to the ECM, and it's failing to enrich the A/F mixture quick enough.

Timing can also cause this problem. Make sure the SPOUT connector is tight, and that the timing jumps advance when you hit the throttle. If there's a delay in the timing advance, or it isn't advancing, then it will have a pretty nasty flat spot too.

Timing won't throw any codes in the ECM. The only signal from the ignition the ECM will flag is the absence of PIP. It does not check to see if the ignition actually advances the timing when told to. If the MAP sensor is "good", it won't set a code either. But, it's a pretty broad spectrum for a MAP sensor to check good on the ECM, but it may not be up to par any more. It IS 20 years old, after all.

ok thanks. yeah it is an 89 f-150 with the 4.9L and SD. i did check the timing when i did the vacuum tests and replaced the TPI Module(my misfire/skip thread)

the timing is set at 10 degrees BTDC (from this weekend)
the vacuum appears to be good overall in the system but i do understand what your saying. what im going to do is replace all the vacuum lines for now and see where that takes me. then i guess ill start doing tests to individual sensors.

 

[d-kuzmen]

well basically i guess it loses all power. it goes from running then drops right down and then it revs. here is a pic of what im trying to explain

Have you checked fuel pressure yet? See what the gauge says when you get on it, the pump maybe getting weak or the filter plugged and it can't feed the fuel fast enough. The fuel pressure should be 45-60psi running and 50-60psi key on engine off.

 

[89frankenford]

Have you checked fuel pressure yet? See what the gauge says when you get on it, the pump maybe getting weak or the filter plugged and it can't feed the fuel fast enough. The fuel pressure should be 45-60psi running and 50-60psi key on engine off.

yup thats already on my list of things to do...problem is im just waiting for the new gauge to come in the mail.

im testing the fuel pressure and the injectors when i get it to try and solve my misfire problem

can you help me on this problem? do you think it might possibly be linked?

http://www.fordtruckfanatics.com/forum/showthread.php?t=14484&highlight=misfire

 

[d-kuzmen]

yup thats already on my list of things to do...problem is im just waiting for the new gauge to come in the mail.

im testing the fuel pressure and the injectors when i get it to try and solve my misfire problem

can you help me on this problem? do you think it might possibly be linked?

http://www.fordtruckfanatics.com/forum/showthread.php?t=14484&highlight=misfire

I checked the pinpoint test for a code 84, now if you've tried that may EVR solinoids with no results that only leaves the wiring or the pcm. Now it maybe possible for the evr ckts to have a short which could open the egr valve at the wrong time causing a misfire. You could also have a lack of fuel pressure that could give you a misfire and also the concern your having now. Try leaving the evr solinoid unpluged for now and see if the misfire stops.

 

[89frankenford]

I checked the pinpoint test for a code 84, now if you've tried that may EVR solinoids with no results that only leaves the wiring or the pcm. Now it maybe possible for the evr ckts to have a short which could open the egr valve at the wrong time causing a misfire. You could also have a lack of fuel pressure that could give you a misfire and also the concern your having now. Try leaving the evr solinoid unpluged for now and see if the misfire stops.

ok i will do that tomorrow and run it for a few days and see what happens...im still waiting for the new fuel pressure test gauge to come in