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DOHC obd 1.5 question by Irrationable
Started on: 12-21-2014 09:13 PM
Replies: 8 (188 views)
Last post by: Irrationable on 12-23-2014 12:09 AM
Irrationable
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Report this Post12-21-2014 09:13 PM Click Here to See the Profile for IrrationableSend a Private Message to IrrationableEdit/Delete MessageReply w/QuoteDirect Link to This Post
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

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Report this Post12-21-2014 09:39 PM Click Here to See the Profile for sspeedstreetClick Here to Email sspeedstreetSend a Private Message to sspeedstreetEdit/Delete MessageReply w/QuoteDirect Link to This Post
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
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Irrationable
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Report this Post12-21-2014 10:01 PM Click Here to See the Profile for IrrationableSend a Private Message to IrrationableEdit/Delete MessageReply w/QuoteDirect Link to This Post
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

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phonedawgz
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Report this Post12-21-2014 11:34 PM Click Here to See the Profile for phonedawgzClick Here to visit phonedawgz's HomePageClick Here to Email phonedawgzSend a Private Message to phonedawgzEdit/Delete MessageReply w/QuoteDirect Link to This Post
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.
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Irrationable
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Report this Post12-21-2014 11:41 PM Click Here to See the Profile for IrrationableSend a Private Message to IrrationableEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
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

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Irrationable
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Report this Post12-21-2014 11:43 PM Click Here to See the Profile for IrrationableSend a Private Message to IrrationableEdit/Delete MessageReply w/QuoteDirect Link to This Post

Irrationable

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Member since Dec 2014
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

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Darth Fiero
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Report this Post12-22-2014 03:54 PM Click Here to See the Profile for Darth FieroClick Here to visit Darth Fiero's HomePageClick Here to Email Darth FieroSend a Private Message to Darth FieroEdit/Delete MessageReply w/QuoteDirect Link to This Post
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

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phonedawgz
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Report this Post12-22-2014 04:55 PM Click Here to See the Profile for phonedawgzClick Here to visit phonedawgz's HomePageClick Here to Email phonedawgzSend a Private Message to phonedawgzEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
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.
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Irrationable
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Report this Post12-23-2014 12:09 AM Click Here to See the Profile for IrrationableSend a Private Message to IrrationableEdit/Delete MessageReply w/QuoteDirect Link to This Post
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

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