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Engine Issue HELP!!!! **UPDATE Post #13**

badmix

badmix

1/2 ton status
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Nov 7, 2004
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Location
West Virginia
I drove my Blazer this morning with no issues, went to buddies shop and did some welding and then drove home. Each way is about 30minutes, Truck ran fine. Im almost home and go to pull out of an intersection and get on the gas some. Not a problem, but now when I was slowing down the truck would stall and now it wont idle. I tried turning up the idle screw just to get it to stay running and this had ZERO effect on it. I had to mess with the A/F screws just to get it to idle. I have a Vacuum gauge mounted in my engine bay, normally it stays around 17hg. Now its barely past 10hg. So I lost almost half my vacuum.

Here is what I did so far

1) Put timing light on it, still running 7* BTDC , so that didnt change any

2) Sprayed Carb Cleaner on every Vacuum line and "T" in the engine bay, this didnt change anything, no change in RPMs when I did this.

3) Adjusted A/F just to get it to keep running.

When I give it gas in Park, the RPMs move up with no problem and it only hesitates a small amount when I first give it gas, more like a stumble.

Any ideas?

A buddy suggest something with the dizzy and the vacuum advance and then he also said something about head gasket between cylinders.
 
sounds like a vac leak to me. Carb mount bolts tight?

Rene
 
Sounds like a faulty accelerator pump in the carb. When the little rubber diaphram tears it causes a drop in vaccum at lower engine speeds, and will cause stalling on takeoffs. when mine went out I had to limp it home alternating from half throttle to full throttle to keep it running, any less than half throttle it would die.
 
Let me know if this makes any sense. I messed with the carb and adjusted the A/F mix and the idle some and it was idling at 1000rpm and stayed running so I could check timing. Timing was fine and I pulled the plug on the float bowls and they were at the level they were suppose to be at. Now when the truck was idling the vacuum was still at 10 and holding steady. But eventually after a full minute or two, the truck would slowly start dieing as if it was running out of gas. I would pump up the gas peddle, start it and it would stay running for a minute and then die.

I changed the plugs, I had some older ones that were decent shape, put them in and no change. I did have one plug that looked pretty messed up, but once I changed them, there was no change to how the truck operated.
 
Sounds like a vacuum leak for sure. I know you said you sprayed carb cleaner around all the hoses and fittings but if I were you I would remove and plug every fitting one at a time until you either find the problem or eleminate it. I would start first twith the vacuum advance hose since the vacuum advance cannister could have ruptured the diaphram.
 
At 1000 rpm the timing should be advancing and you will not get an accurate reading (what it should be at idle).
 
Okay, with the idle adjusted above 1000, the truck will stay running. When I back down the idle below this, it wants to die. but the vacuum would read between 10-12hg and it was steady (meaning no valve train issues from what ive read)

Also, When I pulled the vacuum line off the dizzy it would act all crazy.

I should also add that when I pump the gas peddle, the truck would start right away with no issue
 
Have you tried moving the distributor around to see if you can get it to run with the idle around 550 rpm? It is entirely possible that the timning chain has jumped a tooth and now your timing is way off causing the engine to not want to idle.

This would also cause the vacuum reading to be lower since the cam/crank timing are no longer where they need to be.
 
I did check the timing and loosened the Dizzy hold down bolt. When I moved the dizzy and advanced it to 14*, it would run better. when I took it down to 4* from my org. 7* it would run worse.

Is it possible it did jump a tooth?? How can this be verified? would this cause the Vacuum to read 1/2 what it normally would read, Just reading on the net and this doesnt sound like my situation. jump timing would show up under timing light and Id be getting backfires, etc. This is not the case. Im almost suspecting something in the carb, but dont understand the low HG readings
 
badmix said:
I did check the timing and loosened the Dizzy hold down bolt. When I moved the dizzy and advanced it to 14*, it would run better. when I took it down to 4* from my org. 7* it would run worse.

1) Is it possible it did jump a tooth??
2) How can this be verified?
3) would this cause the Vacuum to read 1/2 what it normally would read
Click to expand...

1) Yes it is very possible

2) Pull all the plugs and have a helper crank the engine while you feel for compression in the #1 cylinder THEN use a socket on the front crank bolt to slowly turn the engine while you have a small screwdriver in the cylinder touching the piston and when the piston moves up to the highest point the screwdriver will stop moving then that is TDC. Now look at the timing mark and pointer to see if they align to zero and if not then either the chain has jumped or the balancer outer inertia ring has spun (more probable with your vacuum issue that the chain jumped).

3) Yes the vacuum reading will drop (how much is anyones guess depending on how many teeth the chain jumped)

You can also check for how much slack is in the chain by pulling the distributor cap, rotating the engine backwards about 1/4 turn then rotate it forward as you watch the distributor rotor and see how long it takes before the rotor turns as you turn the crank.
 
Would bad spark plug wire or cap/rotor cause these issues; no idle below 1000rpms and low vacuum.
 
badmix said:
Would bad spark plug wire or cap/rotor cause these issues; no idle below 1000rpms and low vacuum.
Click to expand...

No, in fact a bad plug wire or plug would cause the engine to idle even lower. Vacuum has nothing to do with plugs or wires. Low vacuum happens from either a vacuum leak, running a "hot" cam, or bad valves (not sealing correctly).
 
***UPDATE***

Okay, my truck (or me) is totally re'tarded. I was up here reseaching everything from jumped timing to cap/rotor to plugs/wires that I kept coming across the "vacuum leak scenerio" and one of the things listed on numerous sites was the PCV being loose or what have you.

So I ran down and had to fiddle with carb to get it to run and idle. I then pulled the PCV hose from PCV and put it back on, wasnt loose or anything and then I pulled the PCV hose from carb, was tight fit and put that back on. I then pulled the hose that goes to the carb that is just above the PCV. That one came off a lil too easy for my taste.


I pushed it back on as far as it would go. Fired up truck, the idle was jacked up, so I started to back it down, when the idle was jacked I would get 12-16hg on the vacuum gauge. I started to back down the idle and it was holding, so was the vacuum at 16hg. hmmm. I then backed it down a lil more and it was still holding. I got it down to 750rpms and the vacuum was at 17hg. I messed with the A/F and it didnt effect it too much.

I was running way rich at first and just leaned it down a bit. I then drove the truck, at first just putting around and then I did a couple "throttle to the floor board" runs. Ran good, idled fine and HG is now holding at 18hg.

This was all with a warm motor. When I get home from work tomorrow, Ill see how the COLD start and running does. Im sure ill have to mess with the A/F some more. I was all over the place trying to get this to run.

Funny thing is , when I was spraying Carb Cleaner I thought I got it up under the carb to those vacuum lines guess not. So, it was either a fluke that it fixed itself , ive got an intermitted problem with my carb or I got lucky.

Truck runs and sounds good, even with 143k on the odo.

Thanks everyone for their help and support.
 
Sounds like you missed it with the spraying the first time around. :waytogo:

Rene
 
Sounds like you missed it, but, did you notice any problems with the brakes?
A brake booster problem can cause a massive vacuum leak that is almost undetectable from the outside with spray.

And sometimes the booster will seem to be working fine, but still be causing a leak.

Of course, if you have hydro boost brakes..........................Never Mind.
 
for good measure I'd cut the hose back an inch and toss a hose clamp on there if its still loose so it wont happen again.
 
I just picked up some new silicone vacuum lines. going to redo them all. And run small zipties to for extra security
 
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