1991 2.5 with partial spark problem

[MJRStang]

New to the forums! And new to the YJ's.

I have been working on this project slowly for a couple weeks now. I picked her up for cheap around 7 years ago and am getting around to working on it.

Previous owner overheated it and I suspect the original engine was blown. (Will not turn at the crank). So I bought another off Facebook. They said it had come out of a 91 as well, but when I got it home and compared the engines it was set up a little differently so I ended up making some mods and switching the intake and distributor to make her fuel injected.

Anyhow, now that I have everything set and installed, I can not get it started. After checking the standard causes (fuel, spark, air) I found my #2 and #3 plugs aren’t firing. 1 and 4 are sparking as they should. I used a known good wire/plug to confirm. I decided to try a new cap and rotor, with same results. Checked the fuel injectors as well and they’re working as they should.

Could this be an ecm problem? I’ve read they’re known to cause starting issues.

Any help would be greatly appreciated!!

 

[ytradio]

From your post it sounds like you are saying that the original engine is a 91 and the new engine that you bought is carbureted. If this is correct then you have a 4.0 and are trying to replace it with a 4.2. If this is correct just changing the intake and distributor aren’t going to work. And I don’t know if the 4.0 system can be made to work on the 4.2.

 

[MJRStang]

Thanks for the response. So it’s not carbureted I believe it’s called throttle body injection? kind of a period between carbureted and fuel injectors. Had a bunch of vacuums into the intake. So I swapped everything out from the original motor which was pretty seamless. To match the harnesses.

 

[ytradio]

Sorry, it looks like I overlooked the number of cylinders that you were checking. I don’t believe that the engine management systems will be the same between throttle body and multi port. Maybe one of the 4 cyl. guys will chime in with more info.

 

[MJRStang]

It’s all good! And it shouldn’t matter, unless I’m missing something everything is the same except block/heads/accessories. I did have to modify the alternator connections but I don’t think it’d contribute to this problem.

 

[deadpool1]

1991, YJ, 2.5L it is. it is MPI EFI injected burns gasoline, It is NOT TBI nor carb it is MPI x4.
The TB has only IAC and TPS, and TV plate, simple as can ever be this.

VIN 8th code P is that; day1 new car engine,
so what transmission is this,. OK M/T i see the TOB there throw out bearing
the A/T box flex plate loves to get wrecked, at A/T install and now CKP is dead or partally dead.,,the ckp is 2 hole types has no hand calibrated gap setting

the distrib is failing 30 year old spark wire sets are totally useless now, resistor wire carbon or silly silicone core are JUNK now.
do the 60k tune up?
just put in new spark kit. cap/rotor,wires hv and plugs, gaped top hood sticker, or 0.032"
cap off see pickup coil is it damaged ? on dizzy (or under cap full of CRUDE sure it is)
the right side of engine block has the stamped (hand) code for year, IIRC last digit is it.
once spark works it starts on instant start spray
an next is fuel filter, and clean injectors.