DPFE issue

[RonSerling]

Everything you say points to clogged mufflers but. A vac guage costs less than 20 bucks at any parts store. That 20 dollar tool is the best diagnostic tool you can buy. It detects vacuum leaks, clogged exhaust, bad valves, even leaking heads. Even on the most sophisticated computer controlled engine a vac gauge is indispensable.

Hook it to a vacuum port on the manifold. Idle vacuum should be 20+hg. If you hit the throttle it should drop to near zero and snap back quick. Hold it open it should stay steady, if it builds up you have a clogged exhaust.

Get the guage...

Dirt !!! Got a vacuum gauge today !!! Plugged it in and started the truck. First thing I noticed at a high cold idle it was at about pulling about 14+HG. When I throttled up it dropped to about 7 but immediately came right back up. I did it a number of times and it did the exact same thing each time !! Then I disconnected the muffler and tried the test again with the same results !!! Gettin frustrated here !!!! Any suggestions ?? Thanks Oh by the way Snapon only charged me $18.99 for the gauge !! ??

 

[Dirtman]

Vacuum is too low. Could be a leak, or bad timing. Snapping back is a good sign. Did you run a test leaving the throttle at around 3k rpm and seeing if the gauge slowly drops?

 

[RonSerling]

Vacuum is too low. Could be a leak, or bad timing. Snapping back is a good sign. Did you run a test leaving the throttle at around 3k rpm and seeing if the gauge slowly drops?

My thought exactly that vacuum is way too low. I have checked it prior to this for vacuum leaks and did not find any but I am not sure how to check the timing and if it is off how to correct it on this engine as I thought it was all controlled by the computer. I did a test at about 2500 and it dropped, to about 3 to 4 +HG, when I hit the throttle but it climbed back up slowly with it at that RPM. Old school was if the timing was off you just loosen the distributor and bump it a few degrees but like I said I am not to sure how to adjust with this distributorless ignition.

 

[Dirtman]

Is this a 4.0 ohv or ohc. On the ohc motors they can jump time (kinda rare). So I'd vacuum leak test it. Youtube... best way is a smoke test but there are other ways.

 

[RonSerling]

Is this a 4.0 ohv or ohc. On the ohc motors they can jump time (kinda rare). So I'd vacuum leak test it. Youtube... best way is a smoke test but there are other ways.

It's an OHV !! Wow a smoke test now that brings back a bad memory !! Back when I got the truck I had a bunch of issues when trying to get it to pass smog. I had a shop run a bunch of tests on it to see if they could figure the issue out. One was the smoke test for a vacuum leak and it proved negative as they said they left in on for two an a half hours and could not find a single leak. Long story short I was getting the codes for running lean and what it finally boiled down to was the fuel pump was failing as the pressure test showed it running at about half the delivery pressure it should be !! Hence the truck was running lean !!! Back to the current issue where as the timing possibly being off like I said before I am know expert but if it is off there is no adjustment beside tearing the front of the motor and replacing the timing chain if I am not mistaken. Thing is that doesnt solve the issue of the DPFE hoses blowing off so I am still trying to figure that out first !!!