I have a 2.0 GA engine that was rebuilt by the PO (professionaly). Had CB Performance FI but was too rich for emisions in Delaware. Don't know if the engine was stock or not. Spent about a year going through the motions to get D-Jet installed and worked out. But it still runs rich. A friend, also on this site, is doing the same so been doing constant comparisons. His engine is now running properly.

Will save the long story - I've been through most of the common pitfalls with setting up this system and have replaced everything, from the obvious (fuel/vac hoses) to the extreme (new injectors). But keep reading and post a thought anyway. Maybe I missed it!

So now it's running strong but still really rich. Don't need a CO meter to know, it's pretty bad. Timing is at 27 deg BTDC. Idle is around 1200 at start up but sounds slow. Exhaust is clear but sometimes black at throttle. Tee'd in a vac gauge in the MPS hose and read 5" hg (should be 15"?). Response is normal at quick throttle, but goes back to 5".

Tested for leaks:
- Pulled all vac hoses and plugged ports at air box - no change
- Sprayed carb cleaner on manifold gaskets while running - no change

Adjusted timing to vac gauge to read 15":
- Idle really high, around 2700 rpm.
- Timing mark for strobe not even in range.
- Turned dizzy back to normal. Idle back to 1200 rpm
- AAR still not fully closed so plugged it. Vac now 3" and idle about 700.

MPS rebuilt from Fuel Injection Corp. and holds steady. Oh yeah, fuel pressure at 28 psi.
Symptoms point to a performance cam. Will map valve overlap using tire rotation on friends car this weekend and compare results to mine to be sure.

If it is an aftermarket cam, I would be interested in a possible trade for a stock 2.0 GA engine. I will be in Hershey. My engine has about 1000 miles on the rebuild. Or, if someone has an MPS that can settle this mess, I really want it!

Sent a PM

TPS is set correctly. ECU knob responds, though not lean enough. I have (2) ECU’s to compare and both respond the same (one I bought from Jeff Bowlsby so I’m pretty confident in that one). Harness continuity was good last time I checked. CHT was replaced.

Seems even with a performance cam vacuum should be much higher. With everything plugged except MPS gauge reads 5” hg. With AAR plugged it’s down to 3” hg.
Does this mean there’s definitely a leak somewhere?

check the MPS stand alone to see if it hold a vacuum.

The thinner diaphram (the variable starting point I told you about) is paper thin and breaks.
If you can hook up a gauge to the MPS and see if it holds a vacuum, that is the first step.
having a gauge inline between the plenum and MPS will not tell you which issue you are hunting.
Could just be a leaky and not super bad MPS.
Put in one that is perfect and you may see its just fine.
See if you can borrow a known good one...someone who has a djet car that runs perfect.

Rich

Bite the bullet, replace the camshaft. Stock is good, and Jake Raby has what he says (and I have absolutely no reason to doubt him) works well with D-jet. NOTHING else will work properly.

The Cap'n

Vacuum decreases with a lumpy aggressive cam, due to overlap between the intake and exhaust events. Having both valves open at the same time (for a little while) helps with scavenging and filling, but it also means that at low RPM some of the intake charge gets pushed back into the intake. That reduces manifold vacuum, which the FI sees as the engine needing more fuel.

Replace the cam, or go to some more adjustable fuel management system. Neither will be cheap...

--DD

Looks like the cam is stock. Mapped the degree of overlap using a cardboard wheel taped to the tire. Jacked up one side as if to do the valves, set to TDC for cylinder #2 and marked point on wheel. Turned through the valve cycle and marked at each point the exhaust and intake were about to close. Placed the cardboard wheel on a friends 73 2.0 set up the same way (his is running fine). The marks line up, and comparing to a degree wheel, the overlap is within a degree of spec.

So, with cam in order, must be a big vacuum leak to read 3". Only thing I didn't replace were the intake rail boots at the air box connection (thought they looked ok). Will replace soon, and will again take a close look at the air box for holes.

Until then any thoughts on causes for a steady low vacuum?

I'm the friend...

Intake and exhaust valves opened/closed at the same marks on the cardboard template mounted to the tire (in 4th gear) for both cars and the angles pretty much agree with the Haynes manual information for the stock cam (how accurate can we be with a cardboard circle, a straight edge and a big protractor? ).

...what Rich said. MPS hold vac alone?

Poor ring seal, leaky valves, combustion chamber leaks.

Anything that can effect dynamic compression can cause this. Time for a compression test AND a leakdown test.

Jake,

The engine was rebuilt within the last 1000 miles. Would it need some sort of break-in to seat everything? Should we do some sort of break-in on it before the leakdown test?

Nice to see the expert chiming in on our rookieness....

I was going to bring that up....did you use a breakin oil and follow break in guidelines to seat the rings?
Low manifold vacuum without vacuum leaks will richen the AFR as at idle the MPS must see 13-15hg to read the idle mix correctly. WOT is 0hg remember.

We got to the "performance cam" conclusion by seeing that the vacuum was at 5", so the MPS thought we weren't at idle, so the ECU started dumping fuel since it thought we were stomping on the accelerator. Today's exercise actually shocked us when we figured that the cam was close to stock.

For those of us that are "search challenged" can you expand on those "break in guidelines"? (pointing to another thread is perfectly acceptable, of course).

Is this it? Engine Rebuild Break in

Next / concurrent problem: Here in Delaware, we need the car to pass emissions testing to get registered (think California). How does one break in the engine without having plates? How about this method "Take the car out and run it up to 5K in second gear and then back out of the throttle without disengaging the clutch. Do that 3-4 hard times and you'll feel the power come up and the rings will be seated." - Jake Raby

Tell me again, where is the vacuum gauge hooked up during this test?
Is the leaky MPS still attached to this gauge while you are testing.

If you have the leaky MPS attached, why are you looking anywhere else beside the leaky MPS?
I recall the MPS has a leak, right? you tested that?
Have you tested the motor with a known good MPS that does not leak?

Rich

The term "Rebuilt" generally scares me these days.. That term is used so loosely.

Yes, a break in procedure is mandatory along with a proper break in oil. You may also have a cracked intake plenum which can result in low idle vacuum and shitty running.

Pretty sure that the MPS was tested using a break bleeder with gauge, separate from the system, to make sure it didn't leak... B, chime in to confirm whenever you start reading this tonight.

MPS definetely does NOT leak. I connected a brake bleeder with a gauge directly to the hose of the MPS, separate from the system - holds steady while pulling 15".

Working yesterday I noticed an 1/8" gap in one of my intake plenum hoses. Hoping that's the smoking gun. Will replace in a couple days and update. Also will look closely at the air box and rails.

Thanks for all the responses!

I want a ride when you get this figured out.

You got it!

Next / concurrent problem: Here in Delaware, we need the car to pass emissions testing to get registered (think California). How does one break in the engine without having plates? How about this method "Take the car out and run it up to 5K in second gear and then back out of the throttle without disengaging the clutch. Do that 3-4 hard times and you'll feel the power come up and the rings will be seated." - Jake Raby
[/quote]

The cost isn't cheap, but what about putting it on a chassis dyno for a number of graduated pulls for an hour or so. You could get some tailpipe emission readings each time, and possibly see things clean up as it break in. This info should give you a better picture of what numbers your looking at before you get to the state station.

Here in Seattle you can get temp registration plates for a day so you can drive a car to have it tested or worked on without getting a ticket for no registration.

Ok, started up with the retard hose from the distributor disconnected and AAR open.

Got 12” hg at 1800 rpm. Squeezed the loose intake boot and got almost 15” (took a couple seconds to build up). Put the retard hose back on and dropped to 5" at 700 rpm.

So I'm going to replace the intake boots and see what that does.

Looked at my records and looks like the engine has about 1250 miles, plus about half a dozen hours from tinkering in the driveway the past few years. With valves adjusted and oil changed many times, I'm figuring it's broken-in enough to not cause these issues. But the new boots will tell.

Will still need to tune on the road, so I'll look into temp tags through DMV.
Thanks all!

Have you checked your Adv/Retard canister for leaks? 30+ year old Adv/Retard diaphragms are usually toast by this point.

Also, check for worn throttle valve shaft - often a source of vac leaks.

Brian

Good point. I checked the canister by pulling vacuum using a brake bleeder and it held. Will check it again. Is there a way to adjust? - doesn’t look like it.

Will check the throttle valve shaft too.
Thanks!