Intermittent Hesitation

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.

Aug 17, 2008
Southern Oregon
So I've been doing some great reading from previous posts to try and fix this really annoying hesitation problem on my 87 60 series. The past few days I've been trying to isolate some emission components using hemostats which seems to work for most of the day but eventually the rig starts to act like its starving for fuel. What the heck could cause this thing to run like a top with plenty of power and then turn it into a hesitating stumbling pile of pooh? My friend the PO reminded me that the dealership told him there was an exhaust leak and the exhaust manifold gasket might need to be replaced. Could this be causing some vacuum pressure problems? I'm not a mechanic so this is becoming more and more frustrating for me. Any ideas?
The exhaust manifold gasket is the same gasket as the intake manifold, so it it is leaking it could be leaking in (vacuum leak) as well as out (exhaust leak).

I was recently having problems and finally found one of the vacuum tubes associated with the HAC (high altitude compensation) valve was spilt. I live at low altitude, but the split hose was letting air leak into the one of the carb circuits leaning out the mixture. So my recommendation is to check all your vacuum hoses.
I second that. If you don't have a vacuum gauge and an emissions manual, I would get both. You can run your vacuum gauge while driving, and see if there's a time when the vacuum drops.

Also, consider fuel delivery issues. Make sure your fuel filter is good, the fuel level in the sight glass on the front of the carb stays at 1/2, and that the fuel lines aren't clogged or deteriorated.

I assume you've bypassed the EGR valve by clamping off the line that goes from the EGR to the EGR modulator (there's several thread that talk about this)?
Yeah, I've tried just the EGR and also the VCV. It appears to fix the problem for most of the day but then it starts doing it again. Its just so random which is the weird thing about it. I'll look into having the manifold gasket done and maybe borrow a vacuum gauge from a friend. I guess stuff like this just makes you appreciate it that much more when things are running good.

Users who are viewing this thread

Top Bottom