IAC's won't produce a code, as they're solenoids. Disconnect at a norm op temp. Idle should take a big dive!

 

I'll try it out. The last one didn't do anything when I disconnected it. Maybe I've got another bad one.

I pulled the vaccum hose off my fuel regulator, didn't really see or smell any gas. The regulator looks on the new side as well as the rails and injectors.

When I have the intake off this weekend is there a good procedure for checking injectors?

Anything else I should replace if I'm going to strip it down to the heads? Valve cover gaskets are a little leaky so they will be on the list. Should I pull the exhaust off and redo the head gaskets while I'm there?

Scott

 

Try re-torquing the valve cover & exhaust manifolds to spec first, in proper pattern. Had the same problems w/ my 87' when I first got it. I just tightened those puppy's down. Then I switched to that "infamous Synthetic oil"! No leaks. (Start soaking the manifold bolt's w/ penetrant.

 

I pulled the vaccum line off the map and the engine died. Is that normal? I've read other posts where people are saying their trucks keep running with the Map taken off vaccum.

 

Im having precisely the same symptoms as you Scott. The only thing I noted was the wires you mentioned. I had a set of cheapies from checker or autozone that lasted about 3 months before I replaced them. Got a decent set of Ford Racing wires for $50 from summit and eliminated that problem.

I think Im looking at an intake manifold leak also. Let us know how youre progressing.

Dave

 

I have yet to see your findings of the TPS numerically. Make sure when you do the test it is up to operating temperature.

 

You mentioned that the exhaust is pinched off? Take a manifold vacuum reading and record idle speed vacuum. Should be between 17-20"HG. Then raise RPM to 2500 and allow engine to stabilize. Vacuum reading should be the same if the engine is breathing well. If not, look at the exhaust. Restricted exhaust can cause the engine to run rich as it will raise manifold pressure and MAP interprets this as the engine is under load. Also remove the PCV valve and place a peice of paper over the hole. Lower intake gaskets that leak will suck air from the crankcase, making that leak hard to find. If those are truly leaking, the paper will suck in and out. Good luck!

 

I will test the TPS again this afternoon and post the findings. I went to measure the vacuum readings this morning. I have a cap on one of the several ports on the top of the intake manifold (I was told this is normal for my year or something.) I put the gauge on it and it read 17"HG I revved it up and it went to 20"HG and stayed. When I let off the gas it spiked up to about 23"HG and then settled down. I will try the PCV valve today as well but wanted to give my findings...

 

With the Engine hot I tested the TPS again. 4.98 volts on the reference signal. .92 volts with the throttle closed, 4.45 with the throttle open. Resistance was interesting though. The book says at closed throttle the readings should be 3.0-4.k and open it should be about 350. Mine were not, although mine matched up with what the pictures showed. 820 ohms at closed throttle and 2230 at open throttle. These readings are pretty much the same as when I measured cold. (If memory serves me correctly..)

 

I did forget to mention one thing I found this morning which seems to help with the hesitation a little bit. The cap that I took off to test vacuum had a tear in it. I replaced it with a new one, so yes I had a vacuum leak there. I have a complete intake manifold set, so this weekend everything is coming off and being put back together.

Scott

 

bump... does anyone know if my pressure is correct or does it indicate a problem? TPS sound normal to you?

 

Yep, that certainly won't improve the function of your engine. Cut that **** off. IMO as long as there's enough back pressure and the exhaust doesn't end under your cab, it's all good . Baling wire is your friend.

Sometimes, all of those sensors that have been thrown at it have overlapping, redundant functions, so the engine could work reasonably well as long as the ECU works. So definitely rule out a huge vaccum leak like the Long Beach cop said, before continuing to throw sensors at the problem. +1 on Arctic Y Block's 0.02, which seems to reconcile all the circumstances you described.

Otherwise, yes, check the resistance and voltage on every wire you can find the specs for.

 

skeith5 did you ever get it figured out! I have a similar issue on my 95 and I do not have the funds to be throwin money at it! I have shot wires till I was blue in theface. I am thinking its head gaskets or intake gaskets!

 

I did have a few intake leaks and things are running better but I'm still having a bit of a problem. I found out that one of the injectors is a 13lb injector so I'm going to swap that out. I'm starting to think that my main problems are more drivetrain/transmission related. If I'm trying to maintain the truck at 40mph give or take a couple everything just shakes like crazy. I'm probably going to take it to a transmission place tomorrow.

Scott

 

Well let me know what you find out. I don't think I have a drivetrain problem. But I did check out my tps tonight and it was spot on per the haynes manual. I did find that my IAC is being weird, when I unplug it the idle never changes, so i will pick up one of those tomorrow from advance, but I did check resistance and it was good however the voltage is what stumped me. When the key is on, engine off the manual says that there should be 10.5v however I am only getting .25v, but if the engine is running then I get around 12-14v. Of all the searching on the web I can not find anything that verifies this!