Ok, here's the setup:

Car; European ITR DC2
Engine; Built B18C 12.7:1 CR, BC Spec IV cams etc, Supertech Retainers, BC Valve Springs, etc.
ECU; P30 Neptuned
Harnass; Ebay OBD2A to OBD1

The problem, first the car wouldn't start.. it kept injecting fuel like crazy.. however, I wanted to rule everyting out so I changed the ECU for a other OBD1 P30, Distributor, Sparkplugs, Sparkplug wires and so on.

Still the car didn't start, so I called up my buddy and he came over with his laptop.. the map read like 10psi, so that explains the injection issue. We swapped the map sensor for a new one, same problem. So we started looking, we changed the harnass for a boomslang, changed the chip.. all the same, still 10psi MAP.. So we thought that the 12V and ground might be the issue, however when we disconnected the MAP the ECU still read a +3,5 Volts on the MAP signal wire!

So that gave us the idea that wiring is a problem, so we hooked up a new 12 Volt wire for the MAP together with a new ground wire, still the same! Than we disconnected all the sensors on the engine, still the same.. so we disconnected the whole engine harnass... STILL 3,5 Volts on the pin and also in Neptune. Than we changed the fusebox in the engine bay, no solution..

But here's the weirdest, when I hookup connector A to the ECU the map reads 3,5V, when i disconnect it and connect the D connector, the map reads 3,5V... so I thought a ground problem to the ECU or a 12V problem.. However, all the grounds to the ECU are 0V and do 'beeb' with the voltmeter, so that seems fine. If I did't know better I'd say the ECU is fried, but with the ECU from my CRX i have exactly the same issue.. also with a other chip in it..

I'm clueless.. Hoping you guys can help us out.

Thanks!

 

Sorry to say. That is a really ugly problem to try and troubleshoot. I would triple check to make sure everything is grounded properly and that there is nothing floating. I would go over everything to and from the distributor again another time.. I would try another ECU aside from the one that you borrowed already and basically redo all the steps you already just did. Are you getting any codes?

 

Multi-wire ground to thermostat gets my vote... goodluck

 

We guessed it was the wiring too, so we hooked up the MAP ground wire to the SG1 ground wire (which is used by the TPS who works fine).

I've used my ECU from my CRX, and it still runs great so that basically rules out the ECU and chip.

There are no codes, because. well.. the MAP sensor does get a signal.. even tho is a messed up signal.

grrrr... hate it.

 

MAP sensor is only 5v.

 

Yes, sorry.. You're right, my mixup in the first post.

 

could be the harness jumper OBD2A to OBD1 mess up, why not try use an OBD2A ecu and see what happen. one thing i dont understand does OEM MAP sensor read boost? 10psi? doesnt it read vaccum only?

 

Ofcourse the MAP does read boost, how else could you tune a boosted Honda?

It just shouldn't read boost right now...

 

so your saying that when your logging what the ECU is seeing, it shows your at 10psi of boost... on your NA motor? sounds like you got some wires mixed up.

run wires direct from the ECU to the MAP sensor. make sure they are going to the right spots on the MAP. one for the 5v and one for the signal, the other can just be grounded to the engine.

 

Yes, but.... The harnass came directly out of a EG civic.. without any problems.. And how would you explain the +3,5Volts on the MAP pin.... when the engine harnass is NOT attached to the car.

 

magic?

 

just to say try useing a p28. or s h i t even a p72 worth a shot

 

I have different ECU's here... none of them make a difference... I'll check with a P73 ECU, maybe that makes a difference, but i'm afraid it doesn't as we've already changed the ECU and Harnass.

 

im not trying to make an argument, only trying to help, it's difficult to diagnose without the actual car, so every tiny clue is important like solving a murder case, from what your saying, +3.5v with engine harness out of the car, so the +3.5v comes from somewhere else, either short to power or back feed, for my b16a three sensors share one power from ecu, could be the jumper harnees tap the wrong wire, try to check without jumperharness, if that dont work, try unplug fuse one by one, see if any difference with the +3.5v

 

Unhook the negative battery terminal but leave the positive hooked up. Next hook a test light up from the negative terminal wire and touch it to something that is metal. If the light lights up then you have a wiring problem. If so there is a draw somewhere giving you those strange readings. Try leaving the volt meter on the map and start pulling fuses if/when the volts change there is a problem in the related fuse/circuit. Hope you figure it out as wiring problems always seem very hard to find.