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Thinking of doing the unthinkable... *Rotor to cap gap. Normal?*

Another thought before you swap the cam out - how are your rocker arms set? If they are out of adjustment they can have a profound effect on your vaccum levels as well. I alway set them with the engine at idle and at full operating temp. Remove a valve cover gasket and slowly back off a rocker arm until it starts to tick. Tighten it back down until it stops making noise then give it another 1/2 to 3/4 of a turn. Repeat for each rocker arm on the engine. Free procedure to do, and could very well cause your issue.
 
So, a chip would be able to compensate for low vacuum? As far as the valve adjustment goes, wouldn't i show low compression on a cylinder that had valves out of adjustment? either way, I am certainly willing to give it a shot before actually swapping the cam.

Anyone know how much a custom burned chip costs anyway?
 
if all the valves are set the same they'd all read the same even if they're not correct, no? longer duration cam will have less vaccum at idle.....a good chip guy should be able to burn correct with all your particulars i guess. i'll be doing the same thing on my '90 soon as i get her. the motor is doing the EXACT same thing you described and i'm glad you posted this. i'm glad for this forum too as things have changed in the last 15 years and i need to learn quite a bit.

thanks, Bill
 
So, if everything checks out and its just the cam causing low vacuum, Who should i go with for a new chip? TBICHIPS.com, or? I would like to spend $100 or less on a chip. Or will a chip even fix anything?
 
Brian at TBIchips.com is certain the guy that I would recommend you to if you do decide to get a chip. He knows his stuff, and is actually able to get fairly close if you provide him with all the particulars of your specific engine.

However, that said, engines are all unique in their fuelling requirements. While a ballpark close enough chip will make a big difference, the best way to do a chip up for your truck is to do it yourself. Buying the equipment to program your own chips for a TBI truck is fairly cheap, and can all be found at moates.net (or .com, can't remember, haha)

It may look quite scary at first, but it isn't that bad of a process if all you are doing is adjusting the VE (volumetric efficiency) tables and leaving the timing and stuff alone to start. Of course, your cam would need to be totally EFI friendly for you to be able to set the VE tables properly by yourself (and is where Brian comes in if it isn't...). Timing can be kind of fun as well, you need to watch the knock counts and make sure you don't get too aggressive with things. Also need to realize that if you change anything in the timing tables, the VE tables will no longer be correct and will need to be adjusted again as well after every go around with the timing. If you really get into things, you can get into some three dimensional adjustments which can really mess with your head.

All this stuff is very well documented on places like thirdgen.org etc, and there is tons of free software available that will do a lot of the hard work for you. Some of the paid software will even auto-tune your chip for you as you drive the truck around (moates ostrich).

That said, all the programming in the world will not overcome a problem like having valves which are too tight. As mentioned above, if all your valves are overtight to the same degree, then your compression will probably stay about the same. The thing about a compression gauge is that it records and displays the max value it sees while you are cranking the engine over. Even if your valves are still cracked open, it will still display some amount of pressure.

That said, 130 PSI is too low for a healthy 350 IMO. I'd have expected between 140 - 160 PSI on each cylinder at the least. You may want to try a wet compression test as well to check the condition of your cylinder rings. Put a little bit of oil in each cylinder to wet the rings before you do the test to see if the compression value changes considerably.

15" of vaccum is fairly low for a mild 350 with the cam profile you have, I'd expect between 18 - 22" instead. Again, if the throttle body does not have sufficient vaccum across it, it will not take an idle adjustment properly (screw bottoms out but still revs too high etc) and if the MAP sensor is reading low vac, it may be entering power enrich mode thinking the engine is under high load to try and compensate.
 
Thank you for all the advise Russ! I am going back and forth on what to do about all this as far as getting chip burning stuff or having one done. I should probably go ahead and do the "wet" compression test. The motor was cold when i took those readings. And i willl go ahead and try again on my valve adjustments. I am convinced that the map is entering power enrichment because i can put a vacuum pump on the map and bring the vacuum up past what its getting from the motor and it will then run like a champ.
 
y5mgisi said:
Thank you for all the advise Russ! I am going back and forth on what to do about all this as far as getting chip burning stuff or having one done. I should probably go ahead and do the "wet" compression test. The motor was cold when i took those readings. And i willl go ahead and try again on my valve adjustments. I am convinced that the map is entering power enrichment because i can put a vacuum pump on the map and bring the vacuum up past what its getting from the motor and it will then run like a champ.
Click to expand...

I had Brian do my chip and noticed a big improvement. He is a really good guy to work with and very helpful. So much so that it probably hurts his buisness. He will sit you down and almost walk you through the process to the point if you then wanted to do it yourself you probably could.

Not only did he burn a chip for me he helped me sort out a clogged cat issue I had and even recommended a great cheap replacement. I even purchased a set of stainless headers from him for an amazing deal. I probably could have gotten by without a chip but after all the help I recieved from him it was the least I could do. Not to mention the truck ran better afterwards!!!
 
Still havent been able to find a leak down tester to borrow so im going to have to buy one. Just wish i could find out why i have such low damn vacuum!
 
I had forgotten a lot about this thread, and did not feel like going back through it tonight, so if asked and answered before, sorry.
But you have checked for an exhaust restriction haven't you?

A partially clogged cat or muffler will cause vacuum problems.

If you have an oxygen sensor, you can unscrew it and adapt a pressure gauge to that port temporarily.
Should not show much back-pressure.

A GM cat honeycomb can break up and clog the output.
 
Dosnt mean a wohle lot but it has a flowmaster 50, and a pretty new(less then 10k miles) magnaflow cat.
 
And just like that something popped into my mind screaming vacuum leak... I can have the IAC shut and un plugged and back the "idle speed" screw all the way out and it will wtill idle with low vacuum.
 
Ok, So, I had a suspicion recently about the egr valve possibly being sticky. So i pulled it off and checked it out. Dont know if its enough to cause my problems, but turns out i can blow threw it! Not big time but it "leaks" enough to blow a mouth full of air threw in about 2 seconds. an entire breath of air can be blown threw in about 30 seconds. So, here is my "fix" Its just to experiment with to see if its the problem.

958090ac.jpg


Lathered a bunch of JB weld in both orifices. If it fixes it i will get another new egr valve. Also found that i could suck threw the vacuum line that goes to the egr solenoid from the throttle body. So i put a vacuum plug on it too just as a further bit of troubleshooting. Should be able to report back with results tomorrow. otherwise it will be tuesday. Fingers crossed but not holding my breath...
 
Well that didnt fix it... still runs as bad as ever. Same situation, the IAC pintle is fully seated, the idle speed screw backed all the way out and still low vacuum. Stupid motor. The sucky thing is, i would like to just get a good used running motor to toss in it but i REALLY want to do a 6.0 in it. The used tbi350 will probably cost around $500 which will put aa pretty good delay on the already very much delayed 6.0.
 
Yep, valve timing might do it, but I keep thinking your other idea has merit.
If the pintal is seated, and the idle screw backed all the way out, it should not idle I don't think.
Double check with a GM guy here, but I think I'm right.
If it is continuing to run, then it has to be getting air from somewhere......
Intake gasket??
 
If it is continuing to run, then it has to be getting air from somewhere......
Click to expand...

This is what hangs me up as well. Not saying its not the problem but i just replaced the intake gaskets about a month ago. Replaced the throttle body base gasket way back when all this started.
 
Fordum is right, the truck should not idle with the IAC forced closed and the idle screw backed totally off. Infact, you want to set the idle around 400 rpm when doing mininum air adjustments...

You may still have a major vaccum leak yet. That said, bad valve timing (or cam timing) or even poor valve lash could be contributing as well.
 
On my Ford, after I had the engine replaced, it ran great, plenty of power, just would not idle right.
The guy who put the engine in and I puzzled over it for a while, and we agreed that it had to be a vacuum leak somewhere.

I could not hang around, but he used some kind of smoke gun or generator to put smoke in the system.
I wanted to watch, to see how the machine worked and how he hooked it up, but could not be there.

Turned out the intake gasket had slipped when he put it on.
Showed up with the smoke test.

He put on a new one, and its fixed the problem.
Not saying its your intake, but if you could borrow a smoke gun, it might show the problem.
 
My next thing i want to do is a combination deal really. I want to pressurize the cylinders(with the valves closed of coarse) with something like 120psi(what ever my compressor is rated at) and listen for air coming threw the intake. at the same time im going to be adjusting the valves.

Fordum, I am feeling very very VERY desavue(sp) at this moment. Did we talk about this once??? At any rate, i would love to do that i just cant come up with a way to do it? Any ideas? I though about a big cigar and filling up a plastic sack of some kind then blowing it in there... and thats the best i got. Otherwise im going to finagle some way just pressurize the intake with about 20psi and listen for leaks that way. Maybe even pull the distributor out so i can listen down that hole for hissing air.
 
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