running lean and i don't know why

[jkeyzer]

I think my 1.7 is running lean, and here is why:

1. spark plugs look whitish - very light grey on one side of the insulator, and have always looked this way since i bought the car

2. if I connect TS1 (airbox temp sensor) my idle drops out and the car is gutless, especially from a stop. really have to slip the clutch to get going

3. oil temps are high after sustained freeway driving in the summer

4. all of this hasn't changed much even after raising fuel pressure into mid 30's psi. plugs are still pretty whitish.

If my car really is running lean, why, and what can I do about it?

MPS is a prime suspect I guess. CHT is new, all vacuum lines are new.

What if my engine was rebuilt in the past to a larger displacement than 1.7?

[Bleyseng]

Has the MPS ever been adjusted? Is it still at the factory settings? Epoxy on the end, rivets holding it together?
Geoff

[Dave at Pelican Parts]

The FI has a number of built-in assumptions. One of which is the size of the engine. A larger engine will likely run leaner, as it will probably be getting closer to the amount of fuel a 1.7 engine would need for the given conditions than what the larger (1910?) would need.

Raising the fuel pressure will richen the mixture, as more fuel will go through the injector per millisecond of opening at a higher pressure than at a lower one. Over 36 PSI the injectors get leak-prone, and atomization will tend to suffer.

CHT and MPS are definitely both suspects.

You probably already know this website, right? http://members.rennlist.com/pbanders

--DD

[jkeyzer]

I have read most of Brad's D-jet site. That's why I am puzzled - everything so far has checked out ok or been replaced, and I am still apparently running way more lean than I should be.

MPS still has rivets and epoxy intact, and is an 049. I have a spare 049 MPS that I will try swapping in to see the difference.

Brain box is a 0 280 000 037, distributor is 0 231 174 007, injectors are the yellow ones, CHT is a 0 280 130 003. Engine is a W case W0035049 which means it is not the original engine of the car (I think it's a 1970 case in a 1972). No decel valve. AAR works, too.

[John Rogers]

Try to find someplace that "pump" the engine so you can find what size it is. If all the other parts are checking okay then you could have a 2l engine with 1.7 FI system. Also what happens if you manually change the resistance of the CHT resistor setting so the eengine thinks it is cold (rich)? Good luck.

[jkeyzer]

I tried my spare MPS today, no change.

[hardflex]

I've tried the resistance trick (with a variable one), I thought I could just dial it in. Results weren't acceptable, and I think i read more recently on Brad's site that it only made a difference in the warm up period, the effect was minimal after warmup. I also tried 2.0 injectors in my 1.7 made 1.8, but it was way too rich (black sooty plugs)

Since it's sometimes less expensive to go big bore than find the original pistons, i'd bet if you're engine's rebuilt it's probably bigger bore. If everything else checks out, you should adjust the MPS. But you can find drilled MPS's cheap, why not get one and keep your original for safekeeping.

[jkeyzer]

What about actually going into the ECU and changing the resistance of one of the resistors that controls the pulse length (how about the resistor network connected to TS1?) to make it richer?

Brad?

[Bleyseng]

Way easier to adjust the MPS. That you can do by ear then go to a dyno shop to get it right on.

Geoff

[jkeyzer]

I've read the MPS article, looks scary to me. Changing one resistor or even adding a potentiometer for mixture control seems like an easier fix.

[74914]

Just a thought, and maybe you've already confirmed that the timing and dwell are set properly? My 1.7's plugs were sooty (opposite your problem), I had a lousy low-end, and had to have the idle bypass screw way out until I checked and adjusted this. Plugs almost instantly changed to a brown/tanish, crisper look and I got better idle & power.

Then of course somehow it all went to *&^%$ after clutch and tranny work?! I've bandaided it for now by setting the timing to <27 degrees (closer to TDC; is that advanced or retarded?) and it seems to run as good as before. I'm using Brad's D-jet site to troubleshoot.

[jkeyzer]

Dwell is at ~48 degrees, doesn't change with RPM more than a degree.

Timing is 27 deg BTDC at 3500 rpm, vacuum lines disconnected. It might have been a degree or two overadvanced and I just brought it back a tad. After a 20 minute drive I still had white plugs. Here's a pic of one (cylinder #1). It's representative of the other 3.

[pbanders]

Originally posted by Dave at Pelican Parts
The FI has a number of built-in assumptions. One of which is the size of the engine.

I don't think this is true. The basic mixture control circuit of the ECU is essentially the same (same design and component values) in all of the ECU's that I've looked at, regardless of engine displacement. A good example of this is the fact that the '73 1.7 L and 2.0L both used the same ECU.

Additionally, fuel pressure is the same for all D-Jet applications, regardless of displacement or cylinder count. And in nearly all cases, the main mixture adjustment of the MPS is the same for D-Jet applications. Those that differ, in my opinion, are examples of where the manufacturers required a tweek to get things right, after problems in running were discovered (e.g. revisions to the initial MPS).

So, how does D-Jet vary mixture by specific displacement? By changing the flow rate of the injectors. The other variations in parameters that are specific to the engine (e.g. VE, cold start and warmup characteristics, full-load transition characteristics) are what distinguish the different ECU's and MPS's that are used by application.

[pbanders]

Jeff, IMO, that plug does look like the cylinder is lean.

One other thing to check - fuel delivery. You can have the pressure test out fine, but due to a clogged fuel filter or a clogged supply line (e.g. the strainer sock in the tank), you cannot deliver enough fuel volume. Look at the procedure in Kjell's article (here on the PP site). I think it's something like a quart in a minute.

[jkeyzer]

Delivery volume is good. I just measured about 1 qt in 35 seconds. This is almost double the minimum rate given in the service manuals.

[Amark]

What is the heat range of that plug. Hard to tell from the angle of the photo.

I had some exteded tip plugs in my car & they always looked lean. The plugs I am running now don't have any of the insulator protruding from the tip & they don't look lean anymore. Went from a Bosch W5 to W7 ???

[jkeyzer]

NGK BP5ES.

[jkeyzer]

Could bad trigger points cause any of this? That's about the last place I have not checked.

I adjusted the valves recently and there was no obvious change. I have checked manifold vacuum at idle before and it was a little low, closer to 10 inches Hg. But I think that would usually cause rich running, not lean.

[dharder]

I just replaced my trigger points due to drivability problems. The car was not running rich or lean- it was just running poorly. It would run great then suddenly start bucking. I disconnected the plug wires at the distributor cap (be careful and quick) and had great spark on all four cyls. I disconnected the injectors, one at a time, while the engine was running and #1 and #4 almost killed the engine. #2 and #3 made no difference- this put me on the trail of the trigger points since they actuate #1/#4 and #2/#3 respectively. After replacing the trigger points, the car has run like a champ without a glitch.

It doesn't sound to me like your symptoms resemble any of the symptoms that I had.

I have a friend with a 76 2.0 that is displaying the exact symptoms that your car is. His car overheats, has no power- especially over 4k rpms, he has to slip the clutch to get it to take off, etc, etc. I've diddled around with it and haven't figured it out. I was kind of hoping that you would figure it out and I (we) would share in the satisfaction of actually fixing something.

His story: he just had his motor rebuilt by a place that installed hydraulic lifters and cam. It has never run right since. I threw a thread out on this website and a few people said that the d-jetronic fuel system and hydraulic cams don't mix. I haven't had the time to really dig into his problem but I will.

Keep us posted.

[jkeyzer]

I definitely don't have a hydraulic cam, as I did my own valve adjustment recently and everything went as planned. But who knows what else is in there. It's not like the car is even that fast, I would be very surprised if there was anything like a 1.9 or 2.0 in there. I have driven a 2.0 and that was a fast car (relatively speaking).