I have an IPD-modified B20 D-Jet ECM (with the remote resistor switch). The ECM itself has a red dial switch to the left of the cooling fins. I understand the remote dial routes through different resistors to fool the air temp sensor, but can anyone tell me what the dial on the ECM itself does? It has no markings on the dial nor are there any on the ECM casing

Thanks all

As I recall -- on all the D-jet brains I've seen, the dial you refer to is gray and has screwdriver slots. It is (or was before being modified) a mixture control. -- Dave

It definitely has screwdriver slots. Should I look into proper adjustment of the ECM dial for mixture or has it been bypassed in favor of the remote dial? When the d-jet car it was pulled from was running, the remote dial was operational but at the time I hadn't seen this ECM dial. I have since acquired a new 142E

I think you would need an exhaust gas analyzer of some sort to really see the difference in running condition. As I understand it--the purpose of the IPD mod is to extend the range (towards rich I guess) of the built in adjuster. -- Dave

I see. Upon looking in my service manual, I see the gray (I had thought it was faded red) knob depicted as a factory adjustment. I will match the existing car's ECM knob adjustment and call it good

Thank you for the knowledge

The grey knob adjusts idle mixture only. If the TPS is adjusted corectly, you will notice the idle quality change as you adjust it. Lean it out fully and turn it up one click at a time until it smoothes out.

The IPD knob does not do anything special that the MPS does not. The MPS has 3 adjustments, one adjusts full load, another part load. Adjusting the MPS correctly means you can have a good mixture at full throttle for max power AND have a lean mixture at part throttle for great economy. The IPD can't do both.
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Three 164's, Two 144's, One 142 & a partridge in a pear tree.

Exactly what I was going to say. Back in the early 70's the federal emissions test Volvo was tiptoeing around was at idle only.

There was some production variances between cars, enough to throw off the finely tuned settings needed too pass the emissions test with out any other added equipment or modifications (lower CR, air pumps, EGR, etc: power sucking crapola).

So on the production line, when the car was complete, they'd hook up an exhaust sniffer on the tailpipe, fire it up, and spend a minute hand tuning it at idle, to perfection, by tweedling that little dial. They'd usually the stick a blob of paint on it to sort of indicate the factory set position.

But whatever tolerances varied enough to make a difference at idle didn't usually make much of a difference at higher throttle settings, so this adjustment was ignored every where else. As soon as the idle contacts in the TPS open up this circuit is disabled.

The IPD adjuster is a bit crude. I used to assume it was just modifying the coolant temp sensor signal, and using that to make the ECU think the motor was a little colder than it was, keeping it in warmup enrichment. But someone more acquainted with electronics said it wasn't just altering the CLT signal, but more directly altering the injector duration circuitry in some manner.

In general, between the MAP sensor (manifold air pressure, the hand grenade thing) and the ECU, the volumetric efficiency curve of the motor was pretty much hardwired in. Since the ECU isn't actually directly measuring the volume of air going in, it just has to make assumptions (based on very stock intake, head, displacement, exhaust) on how much air goes in at a given pressure. Generally speaking a cam change won't be a nice even 10% improvement everywhere, but that's what the IPD box would give you.

Still, a bit better than nothing, for the time. Luckily enough engines without catalytic converters are happy enough burning a wide range of mixtures, you have to get fairly far toward the ends of the bell curve before there are too many ill effects.
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'63 PV544 rat rod, '93 Classic #1141 245 (now w/16V turbo)

I would only add--if you are attempting to set mixture by "ear" -- start from rich and work your way to lean. It's very easy to go too far towards rich -- overshooting the "sweet spot" where you'll only know by looking at the plugs and/or calculating gas mileage. When the mixture gets leaned out in stages the difference is more noticeable (at idle or on the road) if you've gone too far-- then you can dial it back to rich a notch or two. If the mixture is correct the motor should accelerate smoothly and immediately when you race the throttle in neutral. -- Dave

Do we know which way is rich and which way is lean on that ECM grey knob?

To be honest I doubt this IPD ECM is worth the effort. My other 142E was running awesome for years with it and I never moved it from 0. It's just cool to have the knob, I guess

Thanks, guys

Catfishk asked---"Do we know which way is rich and which way is lean on that ECM grey knob?" -- it's been a really long time ---but I always had a way of remembering which way---it seemed all the FI systems got enriched or leaned opposite of a normal carburetor needle valve---that is clockwise to enrich--counter clockwise to lean. I think that's the way the d-jet goes. -- Dave

Thanks for the information. I wasn't able to get the car running properly with the IPD unit, but the original I modified ECM is working fine. I'll mess with it again soon.

I like the cold-start choke idea- that's crafty!

I think the main use was to account for use of IPD's 2.1L kits - B21 sized pistons in overbored B20 blocks.

It needs more fuel, but with a stock cam and head, the flow characteristics were *fairly* close to stock still (in reality, at lower RPM's it pulled more air, at higher rpms, very little extra - as you'd expect from increased displacement with no better top end breathing ability).

You could either mess with the fuel pressure regulator to get more fuel to go through the injectors at the same settings, mess with the MAP sensor if you really knew what you were doing, or get one of these boxes and bump up the calculated injection times a bit.

PS: There was another use I found with my second 1800E. The original ECU dies, and then I discovered it was an early version of D-Jet that had an ECU controlled cold start valve. The vast majority of them used externally wired 'dumb' electrical circuits (combination of the starter being engaged and a temp switch on the block). I couldn't find a replacement early style box in the days before the internet, so I ended up using a later style IPD box. The cold start didn't work, nothing in the ECU to fire it, but on cold starts I could use the knob as an electronic 'choke'. *groan*
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'63 PV544 rat rod, '93 Classic #1141 245 (now w/16V turbo)