SirLapsalot

I have just finished installing an engine out of an '88 951 into my '86 951. I am having a no start issue with no tach bounce. The engine and harness are from the '88 and the DME, KLR and body harness are from the '86. The reason I used the DME from the '86 is because I have a shimmed waste gate along with the chip that I wanted to use from the 86 DME.

My first question is, is there a conflict with using the DME from the 86 when the harness is from the 88 which uses the 28 pin chip?

My problem is with the speed and reference sensors or the DME because of the no tach bounce but I cannot figure out why. The sensors both have around 1k ohm resistance at the DME plug leading me to believe the sensors and wiring are good. I did try jumping/bypassing the alarm but that did not give me tach bounce. The new engine did have the sensor bracket removed so I did have to gap the sensors with an 0.8mm feeler gage. I am fairly confident that the gap is correct but I guess it's possible I somehow bitched that up. My other thoughts are that maybe I damaged my DME removing it??? I tried both the DME from the 88 and 86 and no tach bounce with either.

Lastly I have been cranking with the DME relay removed because I wanted to crank and build oil pressure before stating it up for the first time. Does the DME relay only control the fuel pump or will you also get no tach bounce with a removed relay. I have tried with both the relay removed and installed and never tach bounce but id like to know for sure if I can keep diagnosing with the DME relay removed so I do not wash out the cylinder walls with fuel.

Am I going about this correctly? Am I missing anything? I am thinking I will re-gap the sensors then look at solder joints in the DME next but I'd rather not go to the trouble if I'm missing something simple

Tom M'Guinn

You can mix and match DMEs and harnesses but there are a few things to keep in mind, particularly about the tach. The 86 harnesses use a square red plastic connector from the engine harness to the dash harness, which carries the signal to the tach. The 88 has a black flat connector with more pins (to include oil level and such). Did you connect the tach signal from the 88 engine harness (black flat connector) to the right terminal in the 86 dash harness square red 4 pin connector?

Rogue_Ant

I put up a page, describing the S&R sensor operation here:

http://www.roguetuning.com/crank_angle_sensors

Keep in mind that the wiring deteriorates as well... As a generality, if the car has stock S&R wiring, then I recommend replacing it.

SirLapsalot

No I did not. Thank you as that must be my problem. I was looking online for wiring diagrams so I could determine what the longer black harness is for because I knew there was the oil level sensor but that black connector has many wires so I was a bit confused. I will search now so I can determine which wires to connect.
I have read your page before. Thank you!

Tom M'Guinn

In that case, take a look but I bet your boost gauge is sitting dead too (should jump to 1 when the ignition is on but the motor is off, to indicate atmospheric pressure). If you have the factory schematics for both the 86 (red connector) and 87 (black connector) you can sort the connections. For tach, connect green/black wires in both connectors together, which should ohm out to pin 21 of the dme. For the boost gauge, it's two wires and but one changed colors -- originally red/green and red/white, but changed to red/green and blue.

SirLapsalot

Yep boost gauge does not read atm. Any help on where to look for connector pinouts?

SirLapsalot

Found a few good threads with info, here is one in case anyone stumbles upon this thread sometime looking for the same thing

https://rennlist.com/forums/944-turb...rpm-meter.html

Tom M'Guinn

Sorry, edited that post to give the colors. The boost signal comes from KLR pin 5, so you can ohm out to that on the red/white turned blue wire.

SirLapsalot

Thanks for your help Tom. I now have use of the factory boost gauge and I can now confirm I have a tach signal which will help with diagnosis. I still have a no start issue to deal with tomorrow but it helps to know I have at least some kind of signal from the speed and reference sensors.

Tom M'Guinn

Glad you got the tach and boost gauge working. Are you getting tach bounce/twitch now when you crank the motor?

SirLapsalot

Yep I am getting bounce/twitch when I crank the motor. It sounds like it wants to start but does not fire. It doesn't really sputter or backfire just a constant almost starting sound. I have spark and had some fuel come out of the test port at the end of the rail after loosening it a bit but have not had a chance to really evaluate fuel pressure or look to see if the injectors are squirting. I ran out of daylight and will have to continue looking into it this week.

SirLapsalot

Are pins 31 and 32 knock sensor signals or are they a different trigger associated with ignition or injectors from the KLR? I am getting ready to do some diagnosing on my no start and I want to check every necessary signal going to the DME.

Edit: Looks like my membership expired and I cannot upload any more attachments at the moment. I was trying to attach a picture of the harness plug for the DME that shows what each pin is for. Anybody know what pins I am talking about and what they are?

SirLapsalot

Here is a link to a picture of the pinout:

https://rennlist.com/forums/10369751-post2.html

Tom M'Guinn

DME 31/32 are not the knock sensor inputs. The knock sensor connects to the KLR.

If you have spark, I'd confirm fuel pressure next, and that the injectors are firing. Was the motor running before you installed it in this car? Timing belt aligned correctly? Plug wires in right order? Rotor in place and tight? AFM signal getting to pin 7 of DME? Engine harness grounds tight on bell housing? Great big vacuum leaks (e.g. intake not seated right, couplers off, AOS/ISV hoses mixed up?)?

SirLapsalot

Thanks for the reply. I know the KLR is used for knock detection but does it not have to send a signal to the DME to retard timing? I was just curious what those pins are for.

My next step is to check for fuel pressure and operating injectors but I'm just getting a game plan together for testing inputs if fuel checks out.

I never saw the engine running but I was told it was. Timing is spot on and all vacuum and air hoses should be correct and seats properly but I will be double checking that. Plug wires and rotor are good. Not sure of air flow meter yet as that will be an input ill check after fuel.

Thanks for the tips.