Rough idle, no throttle response, dies when i put it in gear

[Anonymous]

Hey all. I've read through a few posts here and elsewhere about similar issues, but one thing sticks out to me. Someone else was having the SAME issues (below), and found in the end, the root of the problem was a bad tranny modulator! MAN that could totally be my problem.

the issue(s):
hard to start (blubbering, sputtering, very rough) when cold, runs very rough until warmed up (will die without some throttle encouragment), very poor throttle response, clunky shifting, idles ok after warm but tries to die when in gear (THIS is the focus I think).

I know I've carb adjustment issues but not too major ones...I'm working on it
Timing is right. DSII/MSD are new.

It's acting like one or both of two things:

1. vac leak. I took the carb off last night, regasketed, added a tad of RTV and bolted it back on. Don't think I've got a vac leak at the carb.

2. the one thing that sounded REALLY promissing was about the vaccuum modulator on the tranny.

I've got the original Ford-O 2 speed in it. The modulator is the canister at the rear of the tranny right? I have it hooked up to a vac port (one of the two sticking up out of the top surface at the rear of the intake runners) on the intake manifold (OZ2502v). Is that OK or should it be hooked elsewhere? How do I know if it's "bad" and is that something I can replace easily (tranny in the car? and are they available?).

Should I just plug the vac port on the manifold as a test (without driving it, just starting and idling)? Will a bad modulator cause these types of symptoms?

Thanks as always gang!

 

[Mustangaroo]

63DropTop,
Use vacumn gage to adjust you carb, tune for max RPM. Should get between 15 to 20 inches of vacumn, then re time your engine. Also check for vacumn leak at intake gaskets, we have two Auisse headed engines here and it is a very common problem. I have even had leaks at idel and have them close up at higher rpm Good luck

 

[Anonymous]

which vac port on the carb should I be using to adjust the mixture (that's the only adjustment you can make based on vac right?). The dizzie ported vac port reads around 5HG at idle. The port on the base below the plates (manifold vac right?) reads around 20 at idle. I think I just answered my own question about which port to use . It'd be pretty tough to get 20HG at the ported outlet, huh?

YUK! I hate the thought of having to pull the intake! I used the starting fluid test around the intake/head surfaces and didn't sense any leaks there. I'll have to be more thorough with it though to make sure.

Any thoughts on the tranny modulator? Would it be better to hook it up elsewhere (no on the rear intake ports)? Maybe it's leaning those rear runners out. How about at the big manifold port at the base of the carb (I could T it off from the PCV)?

 

[CobraSix]

I had no issues with leaks on the intake, mainly because I RTV'd the living crap out of the gaskets.

The thing that got me, double check all vacuum ports. I went to loops for about 2 weeks until I found one vacuum port on the back of the carb I couldn't see once I put the carb on the car.

It could be the vacuum modulator, but I don't know much about them. Simple to fix that...get a T5 (hehe).

If you've checked all the other possible sources, then I think you may be on the right trial.

WHich carb do you have? You should use the vacuum port for tuning that will pull a vacuum at idle. Depending on the carb, there maybe be a number of ports that do this. Just don't use the ported vacuum you would use for the dizzy.

Slade

 

[Anonymous]

I've got the Holley 2300 500CFM carb. I'm pretty sure I've plugged or used all of the vac ports on the carb and the manifold.

I have plans on a C4 upgrade in the future, but I'll need to fix this in the mean time! :roll:

Thanks Slade!

 

[Mustangaroo]

When you engine is running at idel and is running ruff, carefully remove each plug wire one at a time. This will idenify which cyl is missing, check the plug for fouling, relace or clean and look for a leak again! If your getting 20 inches at idel (1000 rpm or less) thats great! Remember if your engine dies when shifted into gear at low rpm something is wrong with trans, but if your rpm is above 1500 rpm (approx) it's your stall converter locking in and causing the engine to die because it's not tuned correctly. I just retuned my son's Aussie 2v - Holley 4V carbed, he was complaining about the exact same thing are you are, I retuned the 4V Carb advanced the timing a little reset the idel to 1100 in park, and fixed the problem. One more thought how is your power valve in the carb? They blow very easy if you have had a back fire up thru the carb?

 

[Anonymous]

No cylinders are missing. My plugs are pretty black. I'm going to drop these Autolites and go back to Bosch Plats.

My idle is right around 1100 in park as well and idle pretty well.

"Remember if your engine dies when shifted into gear at low rpm something is wrong with trans"..that's what I've got. I shift into gear and it drops to low RPM and tries to die. I'm thinking modulator all the way. Could be Torque Converter as well though.

The carb has backfired a few times pretty good...going to replace the powervalve this weekend.

 

[CobraSix]

1100 RPM for park? Isn't that a little high?

THought the specs were like 800 for an Automatic.

Slade

 

[Anonymous]

yep, it is a little high but when you are fighting off low RPM stall....

 

[CobraSix]

How old is the carb?

I'm wondering if you don't have a clogged idle circuit? That or as mentioned..the PV

I've had that happen, and it happened quick (like in 20 miles). By the time I was home, I was having to keep the engine RPMS above 2000 to keep it running.

Slade

 

[Anonymous]

The carb is new. Clogged idle circuit is a possibility as is the PV, but those wouldn't make the thing die only in gear would it?

How do I check/clean the idle circuit?

 

[Anonymous]

I would plug every port except the one used for tuning, I go off the tree on mine(actually I pull it up to a tree and do it in drive) but I mean the vacuum tree. If it is pulling 20" at idle without the needle jumping you shouldn't have a leak. Before I got my dash mounted guage I ran the other inside with a length of hose, very useful tool.

If you hooked up the pcv with those full roller rockers there is an issue with pulling oil through it, (Jimbo).

Is there a known good carb you can try?

Ben is right about the vacuum leaks with the OZ intake. I check mine every couple weeks, often a couple bolts need tightning. I'm wondering if that's because of the pretty stainless bolts I used.

Also you have said there is an exhaust leak at the 3/4, that should make it pretty difficult to diagnose a vacuum leak there with the noise and heat. I had this problem and eventually solved it by pulling the head, having the port divider installed and having it milled flat. My header had to be heated and bent to fit and was warped. My brother welded the flanges together and we had it milled flat too. No leaks so far.

I'd do a compression check, hot wet and dry.

Have you checked to see if the mechanical advance is coming in?

 

[CobraSix]

can you make the car idle at 700 RPM with the car in park?

If you can, then yes, you idle circuit isn't clogged.

Slade

 

[Anonymous]

I think I can get the car to idle in park at lower RPM ok.

The exhaust leak at 3/4 was (is) making a bit tough. I quick-fixed it temporarily with some muffler mender just so I could track down the other issues.

How do I check the mechanical advance? With the timing light on and the vac advance connected, the timing doesn't advance smoothly as I give it gas. It seems to "stick" a bit at first. How do I check to see of the advance canister is working correctly as well?

 

[cfmustang]

Man, this sounds familiar. This is what I have been fighting all Summer and still haven't found it. One difference is the manifold vac though. Yours is much higher than mine. However, I have sprayed every sqaure inch of the engine compartment I can with Carb cleaner and still have not found a leak. Didn't check the transmission though...

 

[CobraSix]

Disconnect the vacuum advance. Have someone slowly rev the engine while you write down the RPM vs. timing with just mechanical advance.

Let us know the results.

Slade

 

[Anonymous]

I'll try to do that tonight or tomorrow and let you know. The DSII is new but I guess that doesn't mean it's all working right!

Any idea which power valve I should be getting?

 

[Anonymous]

I just pulled the old modulator out of the back of my Ford-O and tranny fluid drained out....all of it it would seem. Is this normal? Is the fluid supposed to be draining from there?

Should the vaccuum for that connection be coming from the manifold?

I have an original Ford-O handbook, but it really isn't all that thorough.

 

[Anonymous]

I just pulled the old modulator out of the back of my Ford-O and tranny fluid drained out....all of it it would seem. Is this normal? Is the fluid supposed to be draining from there?

Should the vaccuum for that connection be coming from the manifold?

I have an original Ford-O handbook, but it really isn't all that thorough.

If you pull the vacuum hose off the modulator and see fluid it means the modulator is bad and fluid could be sucked into the manifold. If you take the modulator loose from the tranny for no reason it means you made a mistake so might as well change it anyway as it is cheap. Take the old one with you as they are different.

Yes it should be hooked to the manifolld.

 

[Anonymous]

I didn't see any fluid coming FROM the modulator, but when I pulled it out, i got about a quart of fluid. That's OK? There is supposed to be fluid behind it?