running lean and i don't know why
 

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?

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

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

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.

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.

I tried my spare MPS today, no change.

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.

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?

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

Geoff

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.

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.

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.

http://forums.pelicanparts.com/uploa...8614_small.jpg

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.

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.

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.

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 ??? :D

NGK BP5ES.

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.

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.

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).

I tried adding a 220 ohm ballast resistor to the CHT just to see what the effects were. It made the idle too rich, even with the idle adjustment all the way CCW (lean). I also had some really bad idle-transition performance from a stop when I first started the car after it sat for 10 minutes - the car wanted to die until I rev'd it past 1500 rpms.

Despite all of this, I still had mostly white plugs on #2 and #3, although #1 is intermittently getting black deposits. Could be an issue with that injector or spark plug wire, etc as I saw that earlier when I swapped MPS's too. #4 is a pain to check (VDO CHT gauge thermocouple is on that spark plug) so I have not looked at it since changing the ballast resistor.

I also tried 150 ohms, that still caused my idle to be too rich but didn't really do much else. And I tried 550 ohms, that made my plugs nice and BLACK, and the car hesitated very badly, on the verge of not drivable.

Are your grounds nice and clean and secure?

Jeff, check the trigger points, there's an outside possiblity they're bad.

As for general reasons why you'd be lean (most/all you've checked):

1. Higher displacement than expected
2. Wrong injectors
3. Low fuel pressure
4. Low fuel supply
5. Defective MPS
6. Defective ECU
7. Shorted CHT sensor (but would only be lean during warmup)
8. Totally screwed up trigger points, contacting only intermittantly, causing average mixture to be low (likely you'd have all other kinds of sputtering problems)

If you're really stumped, see if you can rent the VW1218 tester from PP. It's my best tool for immediately evaluating the state of the FI system. Checks all components, including all ECU functional blocks, MPS operation, and dyanamic testing of the temp sensors, as well as a full harness checkout.

That sounds, to me, like an assumption about the size of the engine. It isn't built into the electronics, no. But it is built into the system--they sized the injectors to the engine.

--DD

Sorry, since Jeff was talking about the ECU, I thought when you said "the FI", you meant the ECU. My mistake.

school me here, it's been my understanding that Djet and Ljet are similar systems, the difference being that Djet calculates air flow through the system based on pressure change and volume of the container, in this case the intake manifolds and displacement of the engine, so engine size would be a major factor if it was now %10 larger.

The Ljet actually measures airflow past the air flow meter and injects the appropriate amound of fuel. It is therefore much more tolerant of changes in engine size and can make the adjustments on it's own, to a point.

Am I wrong on this?

So if I am going to adjust my MPS to try and change the mixture, how dark of a tan/brown am I looking for on the plugs?

Also, can I measured exhaust gas composition with the engine rev'd to 3000 as a general indicator of the overall mixture? I think PP has a gas analyzer I can use if I drive up and I'd like to check things out in addition to using the d-jet tester.

I had a little time yesterday to fiddle with my friend's 76 that was (is) displaying some of the same symptoms that your is. I tried swapping his distributor with mine, which has brand new injector points, and it made no difference. Here's what I found:
1) He had his coil hooked up backwards and when I fixed that it ran considerably better.
2) #1 cyl had zero compression. This would explain the gradual overheating everytime he drove it and the basic poor performance. His was a brand new engine rebuilt by AVP in Sacramento with hydraulic lifters and cam and I suspect that there has been a valve train problem since it was new because it was displaying the same symptoms from the get-go.

It doesn't sound like any of this would relate to the problem you're having but you might want to do a compression check.....

What dharder points out is something I emphasize repeatedly on my web page - you MUST be 100% certain that the mechanical condition of the engine and the ignition system are in perfect working order before you take on the FI system as the cause of whatever problem you're experiencing. Often, the best way to do this is to have a new set of eyes look at your car, as they may see the problem that is staring you in the face.

I'm not saying that Jeff here hasn't already done this, just that it's the "zeroth" step of analyizing any FI problem.

make sure you've read Brad's page on the adjustments, and understand it thoroughly.

if you're adjusting without a load or gas analyzer, when you turn the inner screw it's just like adjusting a carb idle mixture screw, just adjust for highest rev's at a constant throttle position. I started about 2500 and the rev's increased when i got the mixture right. I then verified the slope of the transition by unplugging the TPS (you don't want the idle circuit to kick in) and checking the setting at idle speed. Same thing, adjust it for highest speed, smoothest running. If there's a variance in the settings, you'd have to adjust the outer screw accordingly (I didn't have to do that.

I have yet to adjust the full load setting. I was going to go full load up a hill for a sustained period, pull a spark plug, and examine the mixture. Crude, but it might work.

Of course, adjustment with a dyno and gas analyzer would be preferred.

As dharder says, you adjust the small inner screw for the right mix at 2500rpms. Do not adjust the outer screw. Check the A/F at 2500rpms with the analyzer as it should be at 13.7. I have found that adjusting by ear gets you close but still lean.

To set the WOT you can measure the stop plug first before you disassemble it. OR the correct way is to use a inductance meter like the Wavetek to set it. The stop must rest against the diaphram at 0hg otherwise it will stress it and crack it. (try to find a replacement these days).

Geoff

I still wish there was a way to change the mixture inside the ECU. A lot cheaper than getting a $175 LCR meter. And I'm an electronics guy who usually is in favor of spending money on test equipment!

I think if we fully understood the ECU we could find a way to lengthen the base pulse length from the pressure sensing loop, regardless of temperature or pressure, and change the mixture over all RPMs.

It would be great if someone could "reverse engineer" the old analog ECU and make a new (and better) digital one. Could put it inside the old ECU housing to keep the stock look.

Brad Anders has about as thorough an understanding of the analog ECU as anyone does. Searching through his site will show you (at least some of) what he has figured out. There are also circuit board diagrams there, and also availble here on this site.

As for a digital equivalent of the D-jet ECU, check into Megasquirt. Uses the same general concepts as D-jet, but uses modern digital electronics and cheap off-the-shelf parts. It can be programmed to emulate D-jet pretty well; one of the BBS members has done the job already. Do a search on "megasquirt" here on the BBS for a link to his page.

--DD

The ECU's controls the injection pulses and the MPS senses what the level of vacuum in the engine is. Low vacuum equals high flow of fuel, high vacuum equals low fuel flow. The MPS's where set to a calibration for each run of engine type, 1.7, 2.0L etc.
Easy just to adjust the MPS.
Geoff

The ECU is understood fairly well. If you want to add an "overall mixture control", in addition to the one that already exists in the MPS, you can do so by modifying the speed control circuit on the daughter card to provide an overall speed-independent offset. This is essentially what the idle mixture control does, except that its only active when the idle switch is closed on the TPS.

You could very easily experiment with using the idle mixture control by disabling the idle switch in the ECU. While you would lose independent control of the idle mixture, this may not be an issue. You could also duplicate the circuit used in the idle section to duplicate the level offset for non-idle conditions (e.g. get a second pot) if you wanted to.

But, I'll say it again - I think all of this is a band-aid and doesn't get to the root cause of your problem. You need to first find out why you're running lean. If it's displacement, and you're well over 1.7L but still using 1.7L injectors, you should get 2.0L injectors. If there is some other hidden problem (e.g. compression, vac leak, timing issue, etc.), putting a pot on your ECU may fix the symptom, but you'll still be running sub-optimally.

We've discussed this topic extensively on this list and on Rennlist. The problem here is that the MPS is a highly integrated component with the ECU, you cannot easily replace either component without replacing both.

Dave's suggestion of using a Megasquirt (or some other aftermarket FI system) is a very good one. It requires a fair amount of engineering to do it correctly, but now there are a couple of good examples out there. Please note - don't expect that simply switching to an aftermarket FI system will result in some big gain in performance or driveability over a good working stock D-Jet FI system. Converting is more of an issue of addressing the long term maintenance of the car, and of a cost/benefits analysis of whether it is cheaper to fix your D-Jet system or to replace it.

Brad, this aftermarket system looks very interesting to me. I like it because it's designed for an air-cooled VW motor, but, I would like to modify it to work with the d-jet manifold and runners so that it looks stock.

Alfred

----

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If you're actually looking for a useful substitute for the D-jet EFI, I very very strongly recommend researching Megasqurt. Lame name, good system. It'll cost you a couple of hundred to do, if you already have a laptop Windoze computer and soldering equipment--and a complete D-jet system. More if you need to buy other parts. Dave Hunt has a running system, and he has screen saves of his parameters. It will be less tuning than trying to adapt a Type I oriented system like the Redline one.

--DD

One more thing in this discussion - to date, if I'm not mistaken, we're relying totally on reading plugs for the mixture information. While this is a time-honored technique, if you're talking about spending big bucks for aftermarket systems, ECU mods, etc., to fix the problem, I suggest putting some numbers around "how lean" first. Get the mixture tested under load with shop quality equipment so that you can see how far off you are. This can be done either on a dyno with the car hooked up to a gas analyzer, or with in-car analysis (there are some 5-gas analyzers that work off 12V and can be connected to a car while driving). I would go to a local shop that specalizes in emissions analysis for this kind of service.