I ugraded my secondary injectors to 720 cc, from RP. When I put it all back together it's idling really rough with no acceleration power at all. 6-9 months ago had a new engine with carbon apex seals installed. Ran very well after that, a lot of power and quickness. It seems to be running rich, backfires after heavy deceleration. All the plugs are igniting. TPS set properly, BAC working. The only thing I can think of is a vacuum leak, but i was very attentive when putting the hoses back on. Any ideas?

 

i not sure if this is right. but i thought you needed like a s-afc or something for any injectors bigger than stock ?

 

The bigger injectors are the secondary injectors, I'm pretty sure they wouldn't effect the idle since they don't come on till above 3500 RPM's. Thanks though.

 

what year is your car?
earlier FC's used high impedence injectors (13 ohms), while later FC's used low impedence..
I am not quite sure as to the specs of the RP injectors, however almost all 720cc injectors I have seen are all low impedence units and do require you to wire in resistors to each of the injectors (or the resistor pack) in order for them to function properly..
The only high impedence 720's I have seen are like my own, which were originally 550's bored out to 720 by RC engineering..

Check the resistence across the 2 terminals of your old 550 injectors, if they are anywhere near 12-13 ohms, then chances are you've got low impedance injectors in your car (I'm assuming it's an 87-early 88)..\

If that is not the case, and assumeing as you mentioned, all vac lines are connected correctly and securley, you would want to check either the intake manifold gasket, or the grommets and o-rings on the injectors (You didn't reuse the old ones did you?)

 

Okay, I dont want to scare you (besides this is just a possibility), but it kind of sounds like blown engine symptoms. Is is vibrating a lot at idle? Does it barely idle or not idle at all? Does it seem like you have a lawn mower engine up there for power? I would get a compression check done to know for sure.

I know, you are thinking, "How could big injectors blow my engine?" Well the answer is, they can't. But one time when I was working on my engine, I dropped something down the inake runners. This proceeded in to the engine and toasted the front rotor. Now if you were just replacing the secondary injectors, I know it would be difficult to drop something down there since you wouldn't have taken off the upper intake. But again this is just something to look for. I hope for your sake that I am way off though. Good luck!

 

Thanks guys,

The car is an 87 tII, VIN # ends in H0501416.

MasteRX, I considered this. After the nausea passed, I did a compression check. The needle bounces get higher, in stairstep fashion, until about 70-75, where the bounces hold steady. I used a conventional compression guage with the backcheck needle pulled out. Does this indicate trashed apex seals?

Thanx, great forum

 

Hey Guys,

Up top. Any thoughts on my compression readings?


Thanx,

 

hopefully its not blown, good luck with it.

 

For the compression readings, look for three even bounces. If you've pulled the checkvalve on the tester then don't worry too much about the peak readings (its going to vary depending on the tester you have as well as engine condition). If you leave the checkvalve in then you sould be looking for readings above 80psi (Mazda min spec) (my 87TII with 142k miles on it reads 100psi front, 95psi rear with the check valve in). Were the readings the same for the front and rear rotor? If so then you're probably ok.

Henrik
87TII

 

Not sure what this could be without seeing the car and hearing it, but I can relate an almost identicle problem. My Project 86 TII had the smae problem. We were at the track doing some hot laps. Came in after a Mudstain GT lost it and flipped on it's lid. So I come into the paddock, idle to about 185 water temp and about 190 oil temp, and shut off the car. Get out, hang out for about 2 hrs, then get in and start it. The car idles terribly and won't boost for crap. Ended up being a stuck apex seal in one of the rear rotors. Easy rebuild, but it meant bad motor. What you described sounded exactly like what I had. The compression numbers you stated sound a bit low. Did they match the front readings? I would get a Mazda comp test to confirm results.

 

I was wondering if anyone thought that bad fuel might be the culprit. The car's been sitting for about 6 months, through a moderate winter with 3/4 of a tank of gas. It's just a thought, i'm pretty desperate right now for any solution.

Thanks

 

The compression readings were nearly identical for both rotors.
If it is a stuck apex seal, would the ATF treatment help?

Thanx

 

Anyone else have any ideas? I'm completely stumped and running out of money.

Thanx

 

some cheap things that might help it out are new plugs and fuel filter (about $20).

also...are you sure the TPS is adjusted right? i'm pretty sure thats my problem. my T2 will start up fine...then the idle will fluctuate between 1000-1500 until its warmed up, then keep a constant idle...buuuuuuuuut, the it idles at like 1000. i tried to adjust the TPS but the screw wouldn't budge and one of the wires had a tear in it. so maybe the heat of the manifold or intercooler was causing it to **** up. but yeah, check out the TPS and see if its calibrated corretly. but maybe you did this already

good luck man...

 

correct me if I'm wrong, but isn't carbon apex seals for race only, and don't last too long? GREAT compression, but not lasting?

6-9 months amounts to a good amount of driving/THRASHING (at least for me)

When I lost an apex seal in my rear rotor, I barely got my car started (had to push start it after it blew) then it idled so nasty, I was so freaked out!!! afraid I blew my motor... It had barely any power, I had to downshift constantly just to keep up with traffic... And I did compression check.. Bingo...

Get back to me on the carbon seals thing... Thx

 

Racing Beat says that carbon seals are not appropriate for turbo situations because they break too easily when faced with detonation.