Befuddled?

[davkat]

I've been reviewing the topics in our forums trying to find out what the problem is with my stock syclone. After the truck has warmed up I get what feels like a miss or hesitation driving around town at 35 or 40 mph. This started about 2 months ago and had slowly been getting worse. The accelerator doesn't feel linear anymore; when moving from a standing start there is a hesitation then it catches and takes off pretty quickly. This all happens after the truck has been running about 5 to 10 min.

I've replaced the TPS sensor, O2 Sensor, MAP Sensor, replaced the FPR, plugs, wires, dist cap & rotor. I do have datamaster have logged it but everything appears to be normal. I do have a problem that had also developed with the cruise control at the same time. The cruise seems to surge. When I initially set it at 65 it drops down to about 62 when I let off the accelerator then climbs back up to 65 but won't keep a steady speed. Not sure if my two problems are related.

I have checked and replaced any faulty vacuum lines and made sure everything was connected up correctly. Anyone have any ideas?

 

[Jimmy]

Re: Befuddled?

Not sure,but there is a big ass vac port on the back of the TB next to the TPS that should be blocked off. It's as big as your pinkie. If it's not sealed off,you will have a massive vacuum leak that could cause the problems you describe.

Check it out anyways.

 

[hatrik8]

Re: Befuddled?

Do a vac line kit. If you have a cruise issue it might be vacuum related. Couldn't hurt even if you don't solve your problem. When I replaced my vac lines it helped my cruise work perfectly.

 

[BoostedSUV]

Re: Befuddled?

Definitely sounds like a vacuum issue. Not saying it is but those are definitely symptoms of a vacuum issue. Could be vacuum line/cap, tb gasket, upper intake gasket etc. Cruise control is controlled by vacuum so a lack of it will cause it to not function properly and a vac leak will also cause a stumble in acceleration. Do you have a vac/boost gauge in the truck other than the stocker?? I had a similar stumble problem when I used cheap vac hoses and once my truck got warm the line to the map sucked closed and cut off vac supply to the map sensor. I was also have cruise issue bc that line melted closed. Just another idea...

 

[davkat]

Re: Befuddled?

I have run new vacuum lines throughout the truck but have not replaced any of the check valves yet, and I do have that vacuum port next to the TPS blocked off securely. I forgot to mention in my initial post that I had also replaced the fuel filter, PCV valves and am using a 180 deg thermostat.

Where can I get replacement check valves other than the dealer? I looked at my datamaster files again and it appears that when I'm getting the stumbling or miss at a steady speed (in this case around 50) the EGR valve is activated. Regarding pump gas, the highest octane I can get here is 90 so once in a while I'll buy a can of Torco which certainly helps overall performance.

 

[BoostedSUV]

Re: Befuddled?

Did you use good vac lines or the cheap silicone ones? I've made that mistake that's why I'm asking.

I got all my proper check valves from autozone. The company that sells "Help" stuff offers all of them. I have extras if you can't find them.

 

[davkat]

Re: Befuddled?

Did you use good vac lines or the cheap silicone ones? I've made that mistake that's why I'm asking.

I got all my proper check valves from autozone. The company that sells "Help" stuff offers all of them. I have extras if you can't find them.

I used good vac lines made out of rubber, not the silicone type. We don't have Autozone in Alaska but do have lots of parts stores that I can check with.

 

[davkat]

Re: Befuddled?

Do you have a vac/boost gauge in the truck other than the stocker??

No I don't, only the stock gauge. Under WOT conditions datamaster shows my vacuum dropping to -0.4 HG whereas when I looked at a datamaster file on Tooky's site his readings showed 20.94 HG of vacuum under WOT on a stock truck...What gives?

 

[davkat]

Re: Befuddled?

Finally the problems are resolved. I took my truck in to a certified ASE mechanic where my wife works and he discovered the timing was way off! That was one of the things I didn't check thinking that we just set the timing back in Nov, how could it be off now! Oh well, lesson learned.:roll: He also made sure all other adjustments were made to factory spec and now my truck runs great...no stumbles or hesitations. He did check for vacuum leaks and there were none so all was okay there.:tup:

 

[BoostedSUV]

Re: Befuddled?

Well that certainly makes sense now that you say it. Glad you got it straightened out and that it was a simple fix. :tup:

I wonder what caused the timing to move in the first place? Thanks for posting an update!

 

[davkat]

Re: Befuddled?

I wonder what caused the timing to move in the first place? Thanks for posting an update!

Only thing I can figure is either I didn't tighten down the distributor enough and it worked loose over time or it didn't get set right in the first place. Since it was running great back in Nov thru Feb I suspect the distributor worked loose and came out of adjustment enough to cause the hesitation and stumble. BTW this also fixed the cruise control problem as well. A great running stock truck is a beautiful thing :woot:

 

[sly dvl]

Re: Befuddled?

It's possible that the reluctor wheel (star looking thingy inside the distributor) on the dist. shaft has moved. I've seen this happen several times and it of course effects the timing. See this post for more details.... http://www.syty.net/forums/showthread.php?t=67715
If the timing shifts again, you'll probably need to replace your distributor.

 

[davkat]

Re: Befuddled?

It's possible that the reluctor wheel (star looking thingy inside the distributor) on the dist. shaft has moved. I've seen this happen several times and it of course effects the timing. See this post for more details.... http://www.syty.net/forums/showthread.php?t=67715
If the timing shifts again, you'll probably need to replace your distributor.

My dist was new when I received my NOS crate motor back in '07. It was built in '93 and mean't to go in a Typhoon and came from PAS before they shut down. If the timing drifts off again in the near future then I will certainly check the dist. Thanks.