Electrical 91 Lx - Factory Tachometer Issues

I tested the SPOUT wiring to the battery for voltage and didn't find any stray voltage. I do not have a test light.
The black meter lead on the yellow/lt green wire at the TFI (disconnected) and red meter lead on the positive terminal of the battery showed ZERO volts on the 2mVDC, 2VDC or 200VDC scales.

I've mentioned before that when the SPOUT connector is unplugged and plugged in that it does reflect base timing unplugged (10 deg.) and will advance the timing to 14 degrees when plugged in. The engine stumble starts at about 1350 rpms all the way up to 2000 rpms, anything below or above those rpms and the engine smooths out. It does idle a little rough but is exceptable I believe.

SSSlacker said:

I tested the SPOUT wiring to the battery for voltage and didn't find any stray voltage. I do not have a test light.
The black meter lead on the yellow/lt green wire at the TFI (disconnected) and red meter lead on the positive terminal of the battery showed ZERO volts on the 2mVDC, 2VDC or 200VDC scales.

I've mentioned before that when the SPOUT connector is unplugged and plugged in that it does reflect base timing unplugged (10 deg.) and will advance the timing to 14 degrees when plugged in. The engine stumble starts at about 1350 rpms all the way up to 2000 rpms, anything below or above those rpms and the engine smooths out. It does idle a little rough but is exceptable I believe.

Click to expand...

The change in timing shows that SPOUT circuit is working OK. I think we can stop chasing that rabbit.

Refresh my memory; have you done a cylinder balance test?

jrichker said:

Refresh my memory; have you done a cylinder balance test?

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Yes sir, I've actually cylinder balance tested 50% of the time I run codes on the car. I get a 9 and then another 9, this leads me to believe all is well according to my Actron user manual.

So, the resistance to ground in that SPOUT circuit (ECU/TFI disconnected) is no longer important ?

SSSlacker said:

Yes sir, I've actually cylinder balance tested 50% of the time I run codes on the car. I get a 9 and then another 9, this leads me to believe all is well according to my Actron user manual.

So, the resistance to ground in that SPOUT circuit (ECU/TFI disconnected) is no longer important ?

Click to expand...

It is likely that there is something left out of the user manual that describes how it displays an open circuit.

I'm going to buy and install a vacuum gauge on the spare vacuum tree port at the firewall. I don't think the car has a vacuum leak. Every rubber hose in the engine bay is new. I reckon a little peace of mind is ok.
The fuel pressure regulator is set at 39#'s without vacuum and runs around 32-33 #'s when under vacuum.
Timing is set at 10° base and advances to 14° when the SPOUT is connected.
Running the Trickflow twisted wedge "Street burner" top end on a fresh short block 302 bored .40 over.
BBK 70mm throttle body and spacer, FoMoCo TPS set @ .95 volts, FoMoCo TFI and PiP sensor, BBK cold air intake with BBK 70mm MAF sensor matched to 24# FoMoCo 24# fuel injectors, 155 lph Wahl fuel pump.
I'm not running a turbo or supercharger.
Smog system has been removed, vacuum lines were plugged and plugs are installed in the cylnder head where the thermactor piping used to connect.
The ECU is new but the stumble issue happened with the old ECU as well.

Just some info on the car and engine.

Not sure where to go from here but I'm open to suggestions.

Thanks

Bought the vacuum gauge and installed it on the vacuum tree on the firewall with a lengthy piece of hose so I could move it around.

Started the car and it sputtered around 8.5" - 10" inches of vacuum. Slowly as the car warmed up to temperature it slowly climbed up to 13" inches of vacuum. At temperature the engine maintained 13" of vacuum and with the throttle held at a constant 2000 rpms it was pulling 18" of vacuum.

I felt the PCV valve and it was clicking it's little heart out. I pulled the valve cover oil filler to throttle body hose and it made no difference to running/vacuum conditions.

Should I be able to feel vacuum at that hose either at the TB side or the oil filler neck side? If so, I didn't.

Finding vacuum leaks

Revised 04-Aug-2011 to add pintle cap, PCV grommet & power brake check valve grommet to checklist.

There is no easy way to find vacuum leaks. It is a time consuming job that requires close inspection of each and every hose and connection.

Small vacuum leaks may not show much change using a vacuum gauge. The range of "good readings" varies so much from engine to engine that it may be difficult to detect small leaks. The engine in my first Mustang pulled about 16.5" of vacuum at 650-725 RPM, which I consider rather low. It was a mass market remanufactured rebuild, so no telling what kind of camshaft it had. Average readings seem to run 16"-18" inches at idle and 18"-21" at 1000 RPM. The only sure comparison is a reading taken when your car was performing at its best through all the RPM ranges and what it is doing now. Use one of the spare ports on the vacuum tree that is mounted on the firewall near the windshield wiper motor.

Use a squirt can of motor oil to squirt around the mating surfaces of the manifold & TB. The oil will be sucked into the leaking area and the engine will change speed. Avoid using flammable substitutes for the oil such as starting fluid, propane or throttle body cleaner. Fire is an excellent hair removal agent, and no eyebrows is not cool...

The vacuum line plumbing is old and brittle on many of these cars, so replacing the lines with new hose is a good plan. The common 1/8” and ¼” vacuum hose works well and isn’t expensive.

The PCV grommet and the power brake booster check valve grommet are two places that often get overlooked when checking for vacuum leaks. The rubber grommets get hard and lose their ability to seal properly. The PVC grommet is difficult to see if it is correctly seated and fitting snugly.

Fuel injector O rings can get old and hard. When they do, they are prone to leaking once the engine warms up. This can be difficult to troubleshoot, since it is almost impossible to get to the injectors to squirt oil into the fuel injector mounting bosses. If the plastic caps on the fuel injectors (pintle caps) are missing, the O rings will slide off the injectors and fall into the intake manifold.

Fuel injector seal kits with 2 O rings and a pintle cap (Borg-Warner P/N 274081) are available at Pep Boys auto parts. Cost is about $3-$4 per kit. The following are listed at the Borg-Warner site ( BWD - Home ) as being resellers of Borg-Warner parts:
Parts Plus – Premium Auto Parts & Accessories or Auto Value or Pep Boys | Tires | Auto Repair & Service | Car Parts | Car Accessories or Federated Auto Parts

Most of the links above have store locators for find a store in your area.

Use motor oil on the O rings when you re-assemble them & everything will slide into place. The gasoline will wash away any excess oil that gets in the wrong places and it will burn up in the combustion chamber. Heat the pintle caps in boiling water to soften them to make them easier to install.



Diagram courtesy of Tmoss & Stang&2birds



Vacuum leak due to slipped lower intake manifold gasket...

Ask Nicoleb3x3 about the intake gasket that slipped out of place and caused idle and vacuum leak problems that could not be seen or found by external examination. I don't care what you spray with, you won't find the leak when it is sucking air from the lifter valley. It simply isn't possible to spray anything in there with the lower manifold bolted in place.





Determining if you have a leak due to a slipped intake gasket as shown above. This test is only good if you can get the engine to run somewhere in the 1000-1700 RPM range
If your valve cover oil filler & PVC systems are still in the original configuration, try this:
Cap or plug the hose from the intake manifold to the PVC valve with a bolt.
Cap or plug the PVC valve with a piece of hose with a plug or bolt in it.
At that point the only vent for the crankcase is the tube from the oil filler neck to the throttle body.

Disconnect the tube that runs from the oil filler neck to the throttle body. Make sure the oil filler cap is on securely. Start the engine and put your thumb over the end of the tube that comes from the oil filler cap. If you feel suction, there is a leak. Another thing to do is to extend the tubing from the filler neck so that there is enough to stick the end in a jar or cup filled with motor oil. If it sucks up the oil, you definitely have a leak at the underside of intake manifold.

This isn't necessarily the definitive test, but it is the best thing I could come up with on short notice. If there is a lot of blowby, this obviously won't be of much help.

See the picture below to see the breather tube where in connects to the throttle body. It is close to the TPS and runs over the top of the IAC.

See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 wiring Mustang FAQ - Wiring & Engine Info Everyone should bookmark this site.

Ignition switch wiring
http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif

Fuel, alternator, A/C and ignition wiring
http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

Complete computer, actuator & sensor wiring diagram for 88-91 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif

Vacuum diagram 89-93 Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxFordVacuumDiagram.jpg

HVAC vacuum diagram
http://www.veryuseful.com/mustang/tech/engine/images/Mustang_AC_heat_vacuum_controls.gif

TFI module differences & pinout
http://www.veryuseful.com/mustang/tech/engine/images/TFI_5.0_comparison.gif

Fuse box layout
http://www.veryuseful.com/mustang/tech/engine/images/MustangFuseBox.gif

So I guess you're saying I have a vacuum leak?

SSSlacker said:

So I guess you're saying I have a vacuum leak?

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Based on the vacuum readings, I believe that you do have a leak somewhere.


After you have done the simple visual checks and the check for vacuum leak on the underside of the intake manifold, consider doing a smoke test.
Some of the guys here have built smoke machines used to find automotive vacuum leaks. They seem to work quite well and are made mostly with parts you would have laying around in your garage. Check out smoke machine vacuum leak - YouTube and see if there is one that you could build.

Ok, a new chapter has begun.

I will look into things and report back soon.

Thanks JoeR.

First off, I'm of the impression that vacuum is vacuum is vacuum. I have seen other pictures of the bottom side vacuum routing on the upper intakes from different posts throughout the interweb and always wondered if it really maters where what is connected regarding vacuum.

So with that being said..... Do any of you see any problem with the way that my vacuum lines are ran off of my intake? For references sake the throttle body is on the left side out of the picture.

I have removed the upper and lower intake from the engine and found this......
The passenger cylinder head, right in the middle.

The lower intake gasket.... passenger side

The lower intake manifold..... passenger side.

So, I have located a vacuum leak. The gasket was a little further to one side of that port then the other and formed a leak. Prior to me removing the lower intake I checked the torque on all the bolts and found most of them loose (not where you could remove with your fingers) as I had to put 1/4 to 1/2 turns to tighten them to torque spec.. When I put that intake on the car it was one of the coldest nights of the year and I went over those intake bolts 5 times until they didn't need anymore torquing. Thinking it was all good I never gave it a 2nd thought about it leaking in warmer weather conditions but I guess they worked their way loose.

Here is my nightmare.

This is from the night I bought it.

I am glad you found the problem. I tell people that persistence is often of greater value than genius. I am sure that you learned a great deal about troubleshooting and are better equipped to deal with whatever else may pop up.

I hope the find and then the repair makes it all better. I'll let you know sometime next week when the parts come in. I just hope I didn't burn some valves with the leak.

One question JoeR, what about my vacuum set up on the upper intake, does it matter?

Thanks for the guidance jrichker.

SSSlacker said:

I hope the find and then the repair makes it all better. I'll let you know sometime next week when the parts come in. I just hope I didn't burn some valves with the leak.

One question JoeR, what about my vacuum set up on the upper intake, does it matter?

Thanks for the guidance jrichker.

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The only picky vacuum connection is the one for the fuel pressure regulator. Don't tee anything off of it, it should connect directly to the intake manifold. The short vacuum line attached to it greatly reduces the number of places you can connect it to.