The oil in the intake manifold most likely is due to the intake plenum gasket.

 

thanks for the input.


does the plenum leak down into the crankcase, or from port to port, or both?

 

update,

we are running after a fashion.
we pulled the plugs (2 months old) and they looked like diesel injectors, black & sooty.
cleaned the plugs and reinstalled. Then on a hunch, pulled the O2 sensor to open the exhaust. the engine did start and after 5 mins of playing with the throttle it cleaned out a bit and would run. did a check of exhaust flow at the tailpipe output and found that gas flow seemed to drop a bit when the throttle was opened quickly, (and the engine started backfiring out the throttle body).

did a test drive and found the engine would cut out momentarily when the truck was run up through the gears. Seemed to cut out around 4000rpm. it would drive acceptably when part throttle was used.
so we reinstalled the 02 sensor and opened the exhaust ahead of the cat. Soon i think we will replace the cat or swap in a pipe section for testing.

 

I think you're on the right track, no engine can run well or for very long if it can't get rid of its own exhaust.

 

Well, on saturday eve, the engine was running acceptably with the exception of cutting out at high rpm.
So,,, sunday AM we went out and pulled plugs to inspect. Sure enough the insulators were nice and off white and looked good.

So we reassemble things and try to start.
The truck overfuels and stumbles and coughs, but cannot be kept running.
Pull the plugs again and we are right back to the black sooty condition. Seems we have an overfuelling problem. (and probably a plugged converter).
So we pulled the O2 sensor to give the exhaust an outlet, and wire brushed the plugs and got the engine running. Once it was running, it would occasionally load up with fuel and stall if we weren't quick on the throttle to keep the rpm up.

So the questions to the group is;
what is the most likely input signal that could cause the PCM to command full fuel, (coolant temp, or MAP or?
OR has it ever been heard of that injectors "stick on"?
OR has it ever been heard of that the fuel pressure regulator "sticks on" and contributes to the overfuelling issue?

 

Today we replaced the CAT with a glasspack for testing.
And put a new MAP sensor and TPS sensor on.
Also we cut open the harness from the PCM to the injectors to check for bad splices (none found).
Checked the injector coils and found resistance from 14.3 ohms to 15.1 ohms. Each bank was consistent.
After all that, the engine started and runs and idles acceptably, so we started driving round to see how long it would hold up. After about 40 mins in town it seemed not bad, so we ventured out on the ring road. It was ok for about 10 mins except that the engine still cuts out above 3500rpm in full throttle acceleration. While cruising about 60mph after 10 mins, it starts missing and running rough and threatens to stall. We are having a hard time holding road speed.
So we head back onto streets and its randomly missing and then runs "normal" for 5 mins or so, then back to coughing and running rough.
We get no check engine light. The coolant temp holds steady.
Tomorrow we will put a new set of plug wires on to see if that deals with the high speed misfire.

We don't get what could be causing the rough running after driving for a period of time.
Almost seems like after running for a time, and everything is good and hot that we are seeing some component failing or a circuit opening? How to trouble shoot that?
Any thoughts from the group?

 

Update from yesterdays efforts.

AS of Sat PM we had put 50 miles on the truck driving round to test response and driveability.
After sitting overnite, we tested the compression. With a dead cold engine, low reading was 131psi, and high was 138psi with all the rest in between.

Inspected the plugs and these appeared medium tan, which considering the soot previously mentioned indicates they have burnt off most of the fouling. The plugs are currently gapped about 0.40" +/- There was no sign of soot fouling or wet fuel on the plugs this time.

We rerouted the injector harness and cam position sensor harness to produce max distance possible from the secondary wire leads.

We replaced the complete secondary wire set with new.

Tested the TPS voltage. found the replacement TPS we used is sitting about 0.9Vdc at idle, so we will make adjustments next weekend to get down to the 0.7Vdc range.

Retested fuel pressure and found ~42psi with engine not running and ~35 at idle (this was down a little from what i recall last time this was tested, but the engine was running so poorly, last test results may be incorrect)

We rechecked the ground leads. This truck only has a metal braid ground lead coming from the RB cyl head to the firewall. other ground leads come from the harness to various screws on the firewall or inner fenders, so while the harness was apart looking at all the splices, we cleaned the grounds and put them all under one screw on the firewall.

After all that the truck would start cold and miss and run rough for 2-4 mins or so. After warming for a few more mins and revving the engine a bit it would clean up and idle acceptably.

We pulled and replaced the IAC, but the replacement was dead, so we cleaned the original IAC and reinstalled. (believe we see a slight improvement in idle stability after this) Idle speed was about 700-750 on the tach.

Did a vacuum test and got 16 inches and stable. Vacuum dropped when throttle opened as expected, but returned to these numbers repeatedly.

As a test we plugged a replacement coolant temp sensor into the harness and tyrapped it onto the heater hose. The thought was this may fool the PCM into staying in open loop mode and operate on a base fuel map so we could check driveability.

So then we took the truck out on the roads again and driving round town it would operate on part throttle acceptably and idle quality was good.

Under full throttle acceleration it would still misfire and stutter above 3500rpm consistently.

Took it out on the highway last nite and it handled part throttle and would make 60mph fine,,,, for about 15 mins.
After that it started misfiring and losing power, then run smooth for a short time.
The more it was driven, the worse it got.

We didn't get a chance to check vacuum after the drive was over, so have no results to share.

Don't really want to do the intake manifold R/R only to find nothing wrong, but i am running out of things to check.

Please post with any suggestions or points to check that we may have overlooked.

 

forgot to mention that yesterday while the engine was running stable, we checked timing at idle speed and found ~18 deg BTDC and fairly stable.

Got the codes from the dash lamp as follows:
12, (expect this as battery has been disconnected)
17, (we ran it for couple of hours with a test CTS in the open)
24, (as mentioned the tps measures 0.9Vdc at idle, so we will adjust)
27, (we forgot to connect one injector harness and ran the engine, so i think that is what caused this code)

That is it.
Anyone remember how many drive cycles it takes for a code to reset automatically?

 

Hey tried to post it on other sites to get the word around but with no sucess.

 

mine was doing almost the same thing try a new temp sensor around $15 at napa