DOHC obd 1.5 question (Page 1/1)
Irrationable DEC 21, 09:13 PM
So, I've been scouring the internet and haven't been able to find any concrete information on this subject. What does it take to run a 94-95 (obd 1.5) DOHC motor using the obd 1 system available on the 91-93 models? I know that the 94-95 model has an additional cam position sensor and uses a MAF sensor instead of a MAP sensor, but are there any other sensor differences?

I have a new obd 1.5 crate motor, and both an obd 1 and an obd 1.5 wiring harnesses. I'm trying to decide which harness and ECM to use on the swap.

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"The Twins"
'87 GT 3.4 pushrod daily driver
'88 GT 3.4 DOHC swap in progress

sspeedstreet DEC 21, 09:39 PM
I had the same setup, a 1995 crate motor. I also had a 1992 {OBD1) complete junk motor for parts. I just moved the 1992 parts over to the new block. IIRC the only real difference in the harness is the OBD1 did not use a cam sensor. Pretty simple, heck, I did it.

~Neil
Irrationable DEC 21, 10:01 PM
From what I can tell, all the sensors are identical on the two motors with the exception of the MAP vs MAP sensor, and the additional cam sensor on the 94-95 which goes unused. So, what I need to do now is find a 91-93 DOHC in the junkyard so I can pull the map sensor and the intake manifold plug that it connects to.

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"The Twins"
'87 GT 3.4 pushrod daily driver
'88 GT 3.4 DOHC swap in progress

phonedawgz DEC 21, 11:34 PM
All the green connector Weatherpack MAP sensors are the same. 80% of GM engines used it including your existing Fiero engine. So just use the one from your Fiero engine.
Irrationable DEC 21, 11:41 PM

quote
Originally posted by phonedawgz:

All the green connector Weatherpack MAP sensors are the same. 80% of GM engines used it including your existing Fiero engine. So just use the one from your Fiero engine.



Yup, I knew that. What I need to get my hands on is the manifold plug that the MAP plugs into. It is a circular plug with three nipples on it that vacuum lines connect to, as well as a hole for the MAP. On the 94-95 motors (like mine) the hole for the MAP was removed and replaced with a clip to hold the spark plug wires in place. In order to utilize a MAP sensor and convert the engine to obd 1, I'll have to get my hands on this style of plug.

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"The Twins"
'87 GT 3.4 pushrod daily driver
'88 GT 3.4 DOHC swap in progress

Irrationable DEC 21, 11:43 PM
The kicker is that I just saw one in the yard a few weeks ago and didn't grab it. Of course, that car is definitely a cube of scrap metal by now...

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"The Twins"
'87 GT 3.4 pushrod daily driver
'88 GT 3.4 DOHC swap in progress

Darth Fiero DEC 22, 03:54 PM
Besides the CAM sensor, the 94-newer 3.4 DOHC engines also had a 2nd crank position sensor (24x) that resides behind the harmonic balancer.

I know for a fact the OBD2 PCMs need to have the 24x crank sensor hooked up to them or they won't work right. I'm not 100% sure about the 94-95 OBD1.5 PCMs. Could be the same deal, but I have not had the opportunity to test it yet.

Therefore, if you have a 91-93 3.4 DOHC engine, the only PCM I recommend you use with it is a 91-93 3.4 DOHC PCM (SERV NO 16149396) which does NOT require the 24x crank or cam position sensors.

If you have a 94-newer 3.4 DOHC engine, you can still use the 91-93 OBD1 PCM on it. But if you have a 91-93 3.4 DOHC engine, you aren't going to be able to use a 94-newer PCM on it unless you can get the CAM and 24x crank sensors mounted and working properly.

-ryan

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OVERKILL IS UNDERRATED

Custom GM OBD1 & OBD2 Tuning | Engine Conversions & more | www.gmtuners.com

phonedawgz DEC 22, 04:55 PM

quote
Originally posted by Irrationable:


Yup, I knew that. What I need to get my hands on is the manifold plug that the MAP plugs into. It is a circular plug with three nipples on it that vacuum lines connect to, as well as a hole for the MAP. On the 94-95 motors (like mine) the hole for the MAP was removed and replaced with a clip to hold the spark plug wires in place. In order to utilize a MAP sensor and convert the engine to obd 1, I'll have to get my hands on this style of plug.




T it into the FPR and you should be good. Do not T it into anything that drains vacuum such as the evap purge solenoid or the power brakes. The FPR only senses manifold vacuum, thus it will work fine. Otherwise of course a dedicated vacuum source works too.

The 2.8 Fiero has the MAP T'ed in with the FPR.
Irrationable DEC 23, 12:09 AM
Thanks guys. Seeing that the obd1 swap is pretty well documented (there's an entire guide on dohcfiero.com), that's the direction that I'm leaning in. Plus, the obd1.5 harness I have is in pretty rough shape.

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"The Twins"
'87 GT 3.4 pushrod daily driver
'88 GT 3.4 DOHC swap in progress

wilberto OCT 19, 03:07 PM
Are you still recovering steering wheels?