74 2.0L, Running Very Rich, owner quite confused, need diagnostic help Options

[drumsticks2112]

Car fires without a problem, but idles quite rough, and runs very rich, so much so that when the it settles down to normal idles, it floods out. MPS was replaced with a used but tested one recently. When it was last running ( a year ago) it ran a little rich, but nothing like this.

As of now, the CHT is not connected. When it is connected, the RPMs jump up to 4000 and stay there. When the CHT is bypassed with direct grounding of the harness, the results are the same as with the sensor being disconnected.

I have no reason to suspect the injectors, FPR, Decel Valve, or the MPS.
Any and all advice is welcome.

-Todd

[type47]

I thought the CHT had to be connected to run; must be mistaken. Start from the basics: valve adjust, dwell, timing, fuel pressure, vacuum leaks...

[Rand]

Running that rich makes me suspect the MPS (even though you say it has a tested one). Pull the vacuum hose off the MPS and see if that kills it. If it runs the same, the mps is bad or the vacuum hose to it is bad or incorrectly plumbed.

[Dave_Darling]

Disconnecting the CHT will send the mixture very rich. That's one problem. It sounds like that is masking a second problem. Make sure the CHT is in spec, hook it up, then try to determine what the other problem is.

--DD

[pilothyer]

I didn't think an open CHTS would allow the car to start either, I know if you disconnect it and ground the lead that goes to the brain (not the CHTS itself) it will fool the Brain into thinking the engine is warmed up fully and cure the rich running........if in fact the CHTS was causing the rich running....................Jerry

[underthetire]

I had a CHT go bad. Went open when hot. Biatch to find. So yes, I think they will start. The air intake temp sensor will cause rich running to. I would check the throttle position sensor. Calibrate it per the specs.

[CHAZT54]

I am working with drumsticks on this car and have done the following in the last 24 hrs to track down the source of this problem;
I replaced the vac. hose going to the MPS - there seemed to be good vaccum on the MPS end of the hose when running and connecting it to the MPS while running had minimal effect- still flooding out. At the same time I connected the hd temp sensor lead to the inj. harness lead which makes the eng race immediately without moving the throttle body flap.
ALSO - grounding the hd temp lead from the brain had NO effect.
I am beginning to think we are barking up the wrong tree. This car ran pretty good a year ago, albeit a little rich, without the hd temp sensor being hooked up.
In the process of restoring the car over the winter, we removed the throttle body and intake tubes for cleaning and painting and then re-assembled with new gaskets. No other EFI components were disturbed. The throttle valve sensor was recalibrated upon assembly. As stated before, the eng. fires right up but the plugs eventually drown in gasoline at idle.
I have not yet checked the fuel pressure - possible source of the problem?

We are frustrated and open to any and all advice.

CHAZT54

[greenie]

I am working with drumsticks on this car and have done the following in the last 24 hrs to track down the source of this problem;
I replaced the vac. hose going to the MPS - there seemed to be good vaccum on the MPS end of the hose when running and connecting it to the MPS while running had minimal effect- still flooding out. At the same time I connected the hd temp sensor lead to the inj. harness lead which makes the eng race immediately without moving the throttle body flap.
ALSO - grounding the hd temp lead from the brain had NO effect.
I am beginning to think we are barking up the wrong tree. This car ran pretty good a year ago, albeit a little rich, without the hd temp sensor being hooked up.
In the process of restoring the car over the winter, we removed the throttle body and intake tubes for cleaning and painting and then re-assembled with new gaskets. No other EFI components were disturbed. The throttle valve sensor was recalibrated upon assembly. As stated before, the eng. fires right up but the plugs eventually drown in gasoline at idle.
I have not yet checked the fuel pressure - possible source of the problem?

We are frustrated and open to any and all advice.

CHAZT54

My advice,

I fought an intermittent rich condition for a long time...
I bought and installed a new CHT which was defective from Bosch.
I will always check new parts now before I install them.

Pull the CHT , test the resistance at cold & hot temperatures using your stove top and a pan of hot water.

Cold it should measure 2,000 to 3000 ohms.

Hot it should measure less than 1000 ohms.

Trust me the car will not run correct without this sensor functioning properly.

[tod914]

Did you actually test the MPS to see if it holds vaccume? 15lbs for 15mins I think. Do all the EFI parts numbers match up for that model year car? It's amazing what gets swapped out over the years.

http://members.rennlist.com/pbanders/DJetP...htm#Drivability this shows you all the part numbers and causes for fi issues. Good luck.

[Dave_Darling]

...At the same time I connected the hd temp sensor lead to the inj. harness lead which makes the eng race immediately without moving the throttle body flap.

That's a big red flag to me! If the RPMs went over 2K or so, you have a vacuum leak. A pretty large one, in fact. Advanced timing can also raise your idle RPM, but only a smallish amount. Air leaks are the cause of almost all instances where the RPMs climb with the throttle still shut.

Find the leak and fix it. Then start figuring the rest of this stuff out. Do you have any hoses that go straight from the air cleaner to the manifold? You should not.

--DD

[Bleyseng]

does sound like a vacuum leak of misplaced hose to me. Check your hose layout first, then look for cracked hoses...

[drumsticks2112]

Did you actually test the MPS to see if it holds vaccume? 15lbs for 15mins I think. Do all the EFI parts numbers match up for that model year car? It's amazing what gets swapped out over the years.

http://members.rennlist.com/pbanders/DJetP...htm#Drivability this shows you all the part numbers and causes for fi issues. Good luck.

The EFI numbers are correct for all the parts. I personally have not tested the MPS, but before it was purchased it was tested and passed without a problem.


I am in the process of checking my vaccum hoses for leaks, and for correct connections but I cannot seem to find a reliable schematic for the hose routing in the engine. All I have to work from is a shop repair manual, any suggestions where I might find another?

Thanks for all the suggestions guys! (IMG:style_emoticons/default/beerchug.gif)

-Todd

[tod914]

Compliments of Dave. http://www.pelicanparts.com/914/technical_...4_20FI_diag.htm

[drumsticks2112]

Compliments of Dave. http://www.pelicanparts.com/914/technical_...4_20FI_diag.htm

Excellent! Thank you, I will get right to work.

-Todd

[CHAZT54]

Compliments of Dave. http://www.pelicanparts.com/914/technical_...4_20FI_diag.htm

Excellent! Thank you, I will get right to work.

-Todd

OK guys- DRUMSTICKS & I are back on this project. We got the hose schematic from Pelican and new hoses are routed properly.
Then we gave the MPS a proper test with a gauge & pump instead of just the oral test and sure enough- doesn't hold vac. at all.
So I figure, problem solved and order a rebuilt MPS from Auto-ATL and hook it up - -- little change - still runs way too rich. ---DAMN!
NOW WHAT?
When I hooked up the MPS I just plugged in the elect. harness and slipped on the hose w/clamp- did not bolt it down. That thing doesn't have to be bolted down to work properly does it?

Where do we go from here?
The snow will be flying soon and it is still in the garage.
CHAZT

[Van914]

Did you check the adjustment on the FI Brain. I used to run mine 4-5 clicks from closed. CW to rich CCW to lean.

[rjames]

Did you check the adjustment on the FI Brain. I used to run mine 4-5 clicks from closed. CW to rich CCW to lean.

Adjusting the knob on the ECU will change things, but I don't think it's possible able to adjust it enough to make it idle at 4k RPM.

[r_towle]

Start at the beginning.
Remove EVERY vacuum line from the plenum, put vacuum line covers on every port so you have no vacuum lines hooked up.

Now hook up JUST the mps.
Start the car...see if that cures it. If it does, its one of the lines.
Re-install ONE line at a time to find the system that is bad.

If that does not work (you can still get it to idle high)
you have to look at what you did...
That is specifically intake runners, throttle body, and all gaskets that go with that.
Check the bottom of the plenum for a rust hole...use a flashlight into the hole to see if there is a new hole that is not supposed to be there.

I have taken out the whole intake and I clean the head really well, then put a little smear of RTV Copper or Black on both sides of the spacer when I bolt it back to the head...that needs to sit overnight before you start the car.
Clamp the large intake runner rubber tubes on both ends...all of them.
Then, see if it still does it.

Throttle body gasket (is it complete, no missing pieces...use RTV if you have to to ensure you have no leak there.)

TPS setup...use the pic below to set it correctly at idle.
Idle circuit is special in Djet and you need to activate it by setting the TPS correctly...its a no adjustable thing...basically there is only one right way to set it...its not a variable...use the picture below.

Turn the knob on your ECU to zero...start there.
Go up one click at a time and wait ten minutes of running between any adjustment there.

Replace the CHT. check for shorts in the wiring going from the CHT to the ECU (pinout on Banders site)

Many times you will find the old wires break and short out...so its a good time to check the whole wiring harness...
Its time consuming, but simple to do with an ohm meter.

Rich

[Rand]

Like Dave said, idle that fast means there HAS to be a huge vacuum leak.

[drumsticks2112]

Thanks for the additional ideas guys, here is the status:

The throttle valve switch and intake mani gaskets are brand new. The FPS and the FI brain have not been touched since the car ran correctly, so we don't suspect them as being at fault. The TVS was removed and cleaned, and I will check the connections on the circuits when I can -- Which is more accurate for setting the throttle; matching to the picture, or setting with an ohm-meter?

Also, does it make a difference if the MPS is properly bolted in? We have been leaving it loose/unsecured in the bay as we test things.

Thanks again,

-Todd