1995 Monte Carlo had a 3.4 DOHC engine put in a 3.4 OHV engine but cant hook up sensors

Asked by Aug 01, 2014 at 07:51 PM about the 1995 Chevrolet Monte Carlo

Question type: Maintenance & Repair

My buddy has a 1995 Monte Carlo. It had a 3.4 DOHC engine he took out and put in a 3.4 OHV now he cant figure out what to do about the cam & crank sensors. He didn't notice before he installed the 3.4 OHV that it doesn't have the sensors. What does he do to make it run? We are sure the 3.4 OHV has a crank sensor he might be able to hook into but what does he do about the cam sensor?

11 Answers


Do you have the donor car the other motor came out of? If so swap harnesses and ECM to match the motor you have.

No the OHV was a new engine he had setting on the floor when the DOHC went bad so he changed the engines out not thinking about the sensor problem.


The crank sensor will be wired to the ICM in the coil pack. I believe the 3400 and 3.4 TDC have the same 7X sensor. The 24x behind the balancer should hook right up. The 3400 fwd motor has a cam sensor. It is located above the cam at the front of the motor (pass side), under the power steering pump. This should be similar to the TDC sensor. As for tuning the car that will be the biggest issue as the sequential injection system with the maf sensor in the '94 / '95 LQ1 cars has some issues. It is also very hard to modify the tune due to the fact that it is an OBD1 computer with a OBD2 style flash chip, you cannot flash it with a programmer like the newer cars or just swap the chip like the older cars. It may run fine? Might be able to swap injectors to trim the air/fuel.

The problem is is that the one engine taken out has the cam sensor as you stated. The other engine installed doesnt. So what do you do about it? There is no place to put it. The head isnt drilled for it.


Hold on. The original 3.4 DOHC engine, known as the LQ1, that came in the '95 MC will have the cam sensor on the cam tower close to the throttle body. This version of the LQ1 was used for 94 and 95 w-bodies. The 96 and 97 LQ1 is similar but they had some work done to the cam's and intake and switched to the OBD2 computer. The 91 through 93 LQ1 looks the same as the others but it doesn't have the cam sensor in the cam tower or the 24x pick-up behind the balancer. 3.4 refers to the LQ1 for fwd cars and the 3.4 OHV rwd engine in the Camaros/firebirds. The only other engine is the 3400 for fwd cars and this is what I assumed you installed (as the rwd engine has the starter on the opposite side). As far as I know all 3100 and 3400 engines were sequential and had the cam sensor built into the lower intake manifold behind the power steering pump. If it doesn't have this sensor you need to find out what engine it is and what it is out of.


Here is the pic.


Here is a pic of a '97 LQ1 but the cam sensor is the same on the '95. It is in the top right of the head. This is what the monte would have had.


Sorry. Edit above 3400 info. The sensor is mounted to the head beside the LIM.

Correct: Sorry. Edit above 3400 info. The sensor is mounted to the head beside the LIM. But the engine installed looks the same and has the same cast numbers on the heads except the one installed is not drilled for the sensor. It has the boss there but not drilled.


That is very weird. Any way to find out where it came from I am curious now


Have you found out anything else from your friend. Sorry total blew it on the sensor, I kept thinking about it as I have not worked on one in a while and figured that I was wrong. It doesn't go into the LIM or the head, that has to be into the block. The 3.4 rwd and the older 3.1's would not have been drilled. The 3.4 rwd would have the starter bolts on the wrong side, but new ones can be drilled and tapped. More likely is that someone put the 3400 UIM on a 3.1 because it increases flow/power. The 3100 and 3400 had structural cast oil pans while the 3.1 had a regular sheet metal one. Either way here is a cheap way to get it running with out the sensor. The sensor is only there to index the PCM so that it knows which cylinder it is to inject fuel too in the sequential system. It has a fail mode that guesses if the sensor fails. The car should run without it, it will just be worse on fuel. To run the stock pcm correctly you will need the cam sensor. If the block isn't drilled we have to assume that the cam will not have the reluctor ring so drilling the hole is point less without a cam swap. There is place for a dist on this motors, some people run a dist stub up to a sensor to adapt efi to older engines. Your plenum and TB will be in the way. A sensor cannot be used on the crank because it turns twice to every cam rotation and the PCM could not use the signal. The only other option is to swap the PCM. Since you have the 4T60e you need a PCM that can run it also. You will need to find one from an automatic LQ1 car from 1991 to 1993 with the under hood and engine harness. They can be found in the following; Lumina z34, Lumina Euro 3.4, the Grand Prix GTP, the Grand Prix STE or GT and various Cutlass Supremes and internationals (most will have "3400" badges on the front fender). These are MAP (Speed Density) based but only do Multiport injection. I believe the injectors and the MAF to MAP is the only difference besides the cam sensor and the 24x on the balancer? I have a few of each and I can check on wed if required.

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