Engine swap. Now car backfires when cold until warm

[Kloopofadown]

Swapped in a 91 engine about 2 months ago. And since then, everytime I start it up from sitting overnight or even a few hours it will idle alright but if i rev it in neutral WOT it will just hesitate, miss, and backfire. If I just open the throttle a little bit, it will rev up. It'll do this for maybe 2-3 minutes before it starts reving fine and becomes drivable. My previous engine also started doing this to a lesser degree a couple months before i swapped it. What could it be?
I can post videos or sound clips if they will help.

 

[spitfire19]

since you swapped engines, you need to make sure that your timing is adjusted, check all spark plugs to see if any appear wet...too much fuel. I had a studder too but it got fixed after replacing the timing belt and adjusting the fuel delivery.

 

[awdtalontsi1992]

I would check your timing first. Also there are alot of differences between a 90 and 91 car. make sure you make all the switches to maintain compatabilty between parts. If I had to take a guess though I would say it probably has something to do with your coolant temp sensor.

 

[Kloopofadown]

Alright, I will check the timing on either Friday or Sunday. It also misses some when decelerating in any gear. When warm of course. It isnt drivable for a couple minutes after you start it, I got it pulled out into the parking lot and just had to sit there while I waited for it to warm up. Kinda embarrasing.

 

[Kash]

Did you make your sure plugs are not fouled, and are gaped correctly?

 

[Kloopofadown]

I'll check those along with the timing

 

[Kloopofadown]

Ok I check the spark plug gaps and they were gapped way too short (about .030) regapped them to .04. Still same symptoms, I'm checking the timing now.

 

[Kloopofadown]

Alright, I tried to adjust the timing, doing everything right according to the vfaq (...timin.html) and as i turn the cas towards what I think is the correct mark there seems to be a point where the idle just drops and becomes real lumpy, I checked the timing mark then and it shows it went way past my target. Then when I turn it back the Idle will jump up and the mark is way on the other side again. Also, during normal driving, the engine seems to cycle between these two stages, low chugging idle almost and sometimes dieing, and high idle . It idles low for 1 minute out of every 10 minutes of idling high. These 2 different idles have nothing to do with the AC fans, or the AC compressor. What else operates with a cyclic behavior that would affect idle?

My engine is a JDM and the ignition timing marks dont seem to make much sense to me can anyone point out which mark I should align the one on the Pulley with?


My ISC is bad, is it better to just unplug it?

Second problem

My Tach is also dead. The noise filter is plugged in. The coilpack is from the old engine when the tach was working. Are there any tests I can do to the tachometer itself?

Well I hope that covers the problems so far. I ended up with the timing way off. I revved it once and got a nice big backfire. I left it there as I dont need to drive it anywhere during the week.

 

[Kloopofadown]

Ok i found one problem. The brake booster hose that goes from the intake mani to the booster has a leak in it. When I shut off the car and hurried over to that area I heard a hissing noise. With that spot on the intake mani plugged it idles lower, closer to where it should be.

 

[hereitcomes]

How does a brake booster leak tie into a cold idle and WOT backfire problem? That doesnt sound right.

 

[Kloopofadown]

It's just one of the many problems.

I adjusted the Closed throttle position switch, it was holding the throttle plate slighty open and causing it to idle too high. Now it idles at the right RPMs but still misfires intermitently all the time except when I get on it ( the throttle), and is still undrivable when cold.


I am going to set the timing but I need to know which mark to line it up with on the picture a couple posts above.

Thanks for all the help so far.

 

[BISHILVR]

Coolant temp sensor?

 

[redeclipse7782]

I def wouldnt "get on it" until you know your timing is right. Doesn't seem like you did a boost leak test if you found the brake reservoir leak accidentally. I would re-check your timing cam/crank and base, and do a boost leak test before driving the car especially "getting on it." Since its NT just put the boost leak tester on the throttle body, fill it up and see if you have any vac leaks. Also do u know if your o2 sensor is good? Do you have any check engine lights on?

 

[Kloopofadown]

Okay I finally got a Laptop with TMO software on it to read the RPMs for the settage of the timing. The timing is now spot on. 5* BTDC base.

It still is undrivable when cold.

My TPS will only go up to 90% or so now that I readjusted it to 0% with a closed throttle (which improved driving in the parking lot immensely).

My ISC is GOOD XD.

I have a 91+ throttle shaft installed on a 90 throttle body because 1- I like the wooshing noise it makes at idle and 2- The 90 TPS was bad. I'm using two big seals and on the side that's supposed to have a small seal I supplemented the big seal with an o-ring to push against it.

I'm not sure how many PSI I should push for the boost leak test, Also, I cannot find anywhere to buy a valve stem for the boost leak tester so if anyone has any Ideas, now would be the time to chime in. What store should I buy one from?

I have a check engine light for ...I'm not sure. My TMO logger wont pull the codes but under DRB for version it says "11 Oxygen sensor | 14" and only shows half of the 4, those both are codes the 14 is throttle position sensor. I bet there are 1 or 2 more codes listed. This leads me to beleive I have a corrupted version of the logging software as I cant view any of the other tabs on DRB. Could anyone email me their copy of the software? I can email my copy to you first and see if it works correctly on your setup and to prove I'm not stealing either.

The O2 sensor IS bad, I think, it should be cycling at idle right? It isnt, it just sits still.

As stated above, I have a logger now so I can post logs WOOT