Help w/ rebuilt engine - vacuum rises w/ rpm

[TheUser]

I got my engine back in last week and got it started and timed yesterday and it runs, but is sluggish and basically has nothing above 2500 rpm. I will say that the only exhaust hooked up for now is headers and h pipe, no mufflers or tailpipes for now until I can get some band clamps or something. This just for tuning the car, I will fix the exhaust before I actually drive it.

Anyway, I got the timing light on it and set it at 10-12 BTDC, firing order is correct (1-3-7-2-6-5-4-8) and goes counter clockwise. All spark plugs are installed and wires hooked up. The weird thing is that my autometer vacuum gauge in my gauge cage shows about 7 hg of vac at idle and then when I rev, it increases the vac...it should decrease vac w/ rpm. I hooked up my hand-held vac gauge to the same spot as the autometer was hooked up to (front port on cobra intake by throttle body) and it pulled 16 hg vac at idle and also increase vac w/ rpm.

The only thing I could think of is that maybe my rockers were loose or something, so I checked them this morning and they're all torqued to 20lb's (stock pedestal mount's).

I've also reset the TPS (I know it has nothing to do w/ the vacuum problem). It's .99v at idle, but when I go WOT, it goes to like 5.65v...shouldn't it be below 5v?

 

[TheUser]

I've checked to make sure the distributer is stabbed on the compression stroke, and it is. Timing was set to roughly 10 degrees, maybe 12 w/ the spout out. Fuel Pressure is set to 39 vac off. When I hook the vac back up, it only drops to 36-37 because I'm not pulling much vacuum.

I installed the timing chain dot to dot.

The car idles fine and I guess it runs ok to about 2000 rpm...maybe could run better, but it really starts to dog out around 2500 and sometimes it backfires, other times it doesn't, but the RPM's climb really slow and it just runs like crap.

Anyone think it could be bad gas? This gas has been in the tank for probably over a year.

I haven't checked my fuel pressure at higher RPM and it's raining today, so I might not get the car out (the top end is off anyway right now from tightening the rockers).

I still want to know why it increases vacuum with RPM. Possibly with the increase in vacuum at RPM, the vacuum is obviously sucking more on the fuel pressure regulator (opposite of what it's supposed to do) and I'm not getting enough fuel. Still, that brings me back to why the hell would vacuum increase with RPM?

Oh, and I've never used these injectors before; I bought a set of 24lb injectors from a guy off of the corral along w/ a Pro M Mass Airflow Sensor mounted on a C & L MAF tube (whatever the thing is that the sensor mounts to).

 

[mustangillusion]

does sound like its running on all 8..im no expert by any means but to me it kinda sounds like a head/valve problem?

 

[Hickfied]

I thought that the vacuum was suppost to rise with RPM? The more the engine revs, the more air it takes in, and the more it is sucking through the vac tubes?

 

[mustangillusion]

Sounds logical..but i have never had a vacuum gauge on a car for long enough to notice. I always just got my reading and took it off.

 

[bluevenom867]

I beleive that what it is supposed to do,like Kickfied said.

Unless its wide open (or you got a large throttle body and cam),vacuum should rise with rpm.If it doesnt,you have a good amount of exhaust restriction.

The runing ruff is something else....

The MAF is calibrated for the injectors?

 

[TheUser]

The way I understand it, vacuum rises with RPM. Consider this: The fuel pressure regulator is attached and controlled by vacuum. When at idle, you have the most vacuum and it sucks on it more, which decreases fuel pressure. However, when you increase RPM, it needs more fuel; consequently, when you increase RPM, you have less vacuum, which allows the regulator to increase fuel pressure to compensate for the increase in RPM's.

The MAF is supposed to calibrated for the injectors and it's labed on the sensor "24 lb".

I was going to pull the codes, but apparently my check engine light doesn't work; it doesn't light up when I turn on the key or anything. I also don't have an analog voltmeter.

 

[bluevenom867]

The way I understand it, vacuum rises with RPM. Consider this: The fuel pressure regulator is attached and controlled by vacuum. When at idle, you have the most vacuum and it sucks on it more, which decreases fuel pressure. However, when you increase RPM, it needs more fuel; consequently, when you increase RPM, you have less vacuum, which allows the regulator to increase fuel pressure to compensate for the increase in RPM's.

I think your a little off,it works that way at full throttle,but at part throttle the engine does not need a large volume of fuel.At part throttle,even though rpms are increasing,the air volume and fuel volume will stay linear (or should) because
the valves are opening a closing faster,it has less time to get air/fuel into the chamber.Witch should provide leaner cruising and better mpg.

At WOT in need more fuel,because you increase the airflow.

Its most likely some problem with a sensor or ground....

 

[vristang]

Oh, and I've never used these injectors before; I bought a set of 24lb injectors from a guy off of the corral along w/ a Pro M Mass Airflow Sensor mounted on a C & L MAF tube (whatever the thing is that the sensor mounts to).

The Pro-M meters modify their MAS, so you don't want to use a Pro-M MAS on a C&L meter. Put the stock F1ZF marked MAS on the C&L.
This should help.


Try setting your tps down to about .7v (anything between about .6v to 1.1v is ok with the computer)
This may get your wot setting under 5v


I thought I saw that you had the vac line hooked up at the TB?
This is not a good place to run a vac line, as this is not indicating Engine vac.
Engine vac is a measure of how hard the engine is working to ingest air. In other words how hard the engine has to pull on air, to get it past the TB.
Putting the line in front of the TB will not indicate engine vac.
Besides, you want that line hooked up to the valve cover, so that the pcv system can function properly.
Maybe I misread that though?

jason

 

[TheUser]

That's the exact reason why I think it works that way. The more RPM, the more fuel. VACUUM decreases fuel pressure. The more VACUUM you have the LESS FUEL PRESSURE YOU HAVE. I hope we all will at least accept that. That's why when you set your fuel pressure, you remove your vacuum line (or should).

I'm going to go test the vacuum on my 90 LX 5.0 just to make sure I'm still sane.

Not trying to be rude and I certainly appreciate the help; I'm fairly confident that I'm right on the vacuum thing though.

Vri: The cobra intake has an additional port on the "neck" of the intake, not the throttle body. That's the port the vac line is connected to. My TB to valve cover hose was hooked up. I only have my MAF calibrated for 30lb. injectors and then this one for 24's. Do you mean move the Pro M sensor to my other "intake" part that bolts to the intake tubes?

Thanks:SNSign:

 

[TheUser]

Well, I'll be damned. I guess somewhere along, I got confused. I checked vacuum on the stocker and it is increasing w/ RPM. I'll have to go back and read about that junk later. What I thought really makes sense to me, but apparently isn't how things work. I could have sworn Hissin said to get the best gas mileage, get a vacuum gauge and try to keep it at a high reading.

Bluevenom: I apologize if I came off as an ass. I really thought I knew that and I was wrong.

I guess that's a good thing, though, because I had no idea how to troubleshoot this one.

I guess I'll swap the old MAF and 30's back in and see how it runs. I will be angry if I have to buy a new MAF. I don't understand what can be so different about the "tube" its self that the sensor just bolts to.

Thanks for all of the help.

 

[vristang]

Engine vac is not SOLELY dependant on rpm.
Engine vac is more closely related to throttle position, with a secondary influence by rpm.
Trying to relate vac to rpm is going to be very confusing.

TheUser-
Please describe all MAF/MAS combinations that you have.
The bottom line is that the C&L meter will not work with a Pro-M sensor. You must use the factory sensor with the C&L, and change the sample tube for your injector size.

 

[TheUser]

I assume the MAS is the Sensor on top that the computer connection plugs into. I'll assume that the MAF is the actual "tube" that the sensor bolts on to and the intake piping attaches to.

I have:
73mm unknown MAF w/ an unknown MAS calibrated for 30lb injectors.
(I think) 76mm C & L MAF w/ Pro M MAS calibrated for 24lb injectors

 

[vristang]

I assume the MAS is the Sensor on top that the computer connection plugs into. I'll assume that the MAF is the actual "tube" that the sensor bolts on to and the intake piping attaches to.

I have:
73mm unknown MAF w/ an unknown MAS calibrated for 30lb injectors.
(I think) 76mm C & L MAF w/ Pro M MAS calibrated for 24lb injectors

Yes, most people refer to the sensor and the tube as the "MAF". I like to differentiate between the 2 distinct parts (the tube and the sensor), so I use MAF tube and MAS.

The 76mm C&L w/ a Pro-M sensor is an unkown quantity. Pro-M calibrates it's meters by modifying the voltage output of the MAS. C&L calibrates it's meters by changing the sample tube diameter in the MAF tube, and using the factory Ford MAS.
The C&L MAF tube and sample tube are sized to work with the voltage output of a factory Ford MAS (for your computer). Any other MAS will not work properly with C&L.

I suggest using the 76mm C&L with the factory stock Ford MAS for your car. As long as the C&L MAF tube has the correct sample tube for your computer & injectors, it will work correctly.
What color is the sample tube in the C&L 76mm.

jason

 

[TheUser]

the side of the smaller tube inside the MAF tube that points towards the upper intake is colored blue on top - it looks like magic marker to be honest.

My problem is that I don't have a stock MAS. I've heard bad things about C & L, so that's why I bought this Pro M...the dude didn't tell me it was a Pro M MAS bolted to a C & L MAF tube.

EDIT: Blue appears to be the correct size for the 24's, just I need a stock MAS, I suppose. I'm sure that was at least part of the problem.

 

[vristang]

the side of the smaller tube inside the MAF tube that points towards the upper intake is colored blue on top - it looks like magic marker to be honest.

My problem is that I don't have a stock MAS. I've heard bad things about C & L, so that's why I bought this Pro M...the dude didn't tell me it was a Pro M MAS bolted to a C & L MAF tube.

EDIT: Blue appears to be the correct size for the 24's, just I need a stock MAS, I suppose. I'm sure that was at least part of the problem.

For the Fox A9* computers the stock Ford MAS is an F1ZF, but there may be others that will work.
Personally, I would hit the junk yard for one. They are pretty common on the Taurus and T-bird cars.
It should be less than 20 bills?

good luck
jason

 

[just4bob50]

Ive read this thread several times now and Im not sure anyone has it correct. First off make sure that if your useing the vac. distribution port that were stock for the EGR system that the feed is actually the feed and the return is the return. If all 5 ports are used 1 will be feed and 1 will be return. the others will go to the EGR equipment. If the line is reversed depending on were your gauge is plumbed your guage will read vac in the wrong direction. At idle and low throttle cruising vacume will usually be the highest numerically on the guage, except letting off the throttle while the engine is under load puliing the car down in speed. The the vacume will read much higher than idle. Your fuel pressure will increase as your vacume decreases. Fuel pressure will be at its lowest during idle because the diaphram in the FPR is actually alowing most of the fuel to pass through the rails into the return line. As vacume decreases fuel presure goes up becuase the diaphram is closing up in the FPR actually restricting fuel flow to the return line. Vacume is realtive to engine load, throttle position, and specs of your cam, as well as other variables. If your guage is reading the opposite start checking the routing of your lines. The best place to run the lines for the FPR and the vacume gauge is to the intake vac. ports. Hope this helps.

 

[TheUser]

just4bob: Thanks for your input! I'm not sure what you mean by feed and return lines in regard to the EGR. The EGR solonoid only has one port for vacuum, which is hooked up to the vac tree thing coming from the pass. fenderwell. The FPR is hooked directly to the intake, and the intake also has a connection coming from the same vac tree on the pass side. The unused ports on the vac tree are plugged (no smog equipment). I might try another port for the vac gauge connection, but for now, it's connected to the front part of the "neck" of the cobra intake in the area where the EGR spacer normally would be (the cobra omits the EGR spacer).

I've taken the top end of this engine off several times and this is how it's always been and worked fine before, so I'm not worried about those connections so much. The difference with this setup is I rebuilt the engine and I stepped down to 24 lb injectors w/ a C&L MAF tube and a Pro M Mass Air Sensor, which do not work together, as vri pointed out - there's a link in another thread from Friday to an article about the difference in ford Mass Air Sensors as opposed to Pro M, C & L and the like. The C & L needs the stock Mass Air Sensor, which I don't have, so I'll probably just buy one at a junk yard if I can find one, which shouldn't be too bad since they will work off of many other cars including 3.8L's.

Right now, my money is riding on the MAF issues.

Thanks again

EDIT...dang, the only salvage yard I found that has one local wants $50 for it.

 

[vristang]

just4bob: Thanks for your input! I'm not sure what you mean by feed and return lines in regard to the EGR. The EGR solonoid only has one port for vacuum, which is hooked up to the vac tree thing coming from the pass. fenderwell. The FPR is hooked directly to the intake, and the intake also has a connection coming from the same vac tree on the pass side. The unused ports on the vac tree are plugged (no smog equipment). I might try another port for the vac gauge connection, but for now, it's connected to the front part of the "neck" of the cobra intake in the area where the EGR spacer normally would be (the cobra omits the EGR spacer).

I've taken the top end of this engine off several times and this is how it's always been and worked fine before, so I'm not worried about those connections so much. The difference with this setup is I rebuilt the engine and I stepped down to 24 lb injectors w/ a C&L MAF tube and a Pro M Mass Air Sensor, which do not work together, as vri pointed out - there's a link in another thread from Friday to an article about the difference in ford Mass Air Sensors as opposed to Pro M, C & L and the like. The C & L needs the stock Mass Air Sensor, which I don't have, so I'll probably just buy one at a junk yard if I can find one, which shouldn't be too bad since they will work off of many other cars including 3.8L's.

Right now, my money is riding on the MAF issues.

Thanks again

EDIT...dang, the only salvage yard I found that has one local wants $50 for it.

50 bucks is pretty harsh. I hope you can find something, without bustin' the bank.
In my opinion the best yards are the ones that do not inventory what they have. Generally speaking, if you have to find and pull the part yourself, it will be much cheaper.

Bob may have a point on the vac. It should not matter where the vac line hooks into the intake...
However, there may be some issues with being very close to the TB. I would try moving the port for the vac gauge closer to the valves.
I hooked my vac gauge up the the distribution tree, and seem to get good readings there.

jason

 

[TheUser]

Alright.

Wanted to say thanks Vri, I got my Mass Air Sensor in today ($27 shipped off ebay) and got it on the C & L. The car runs pretty good - no dogging out at all, so that was the issue. It only has a VERY slight idle surge where it bounces from about 650-700 to around 800 or so, no big deal and is probably due to the E303 cam. I might try turning the C & L and see if that makes a difference.

The weird thing is that I'm pulling like 19hg of vac at idle; the idle might be a little higher than stock, though(700ish). Before the rebuild w/ the same cam, I was pulling about 14.