mean hesitation over 6k
 

hey guys i was trying to find someone with the same problem but too no luck. heres what i have 1991 fc na. has a corksport radiator, racing beat header, and a handful of other little things. Now to the problem, when accelerating, when i get over 6k rpm it backfires, stutters, and cuts out to the point of me not wanting to drive it anymore (dont want to further hurt the problem). i was told by the previous owner i need secondary injectors. i dont know if he knew his stuff or not and wanted to see what some rotary smart people have to say. also when starting the car it seems to not want to start right away...when given just a bit off gas it starts right up and idles fine. i dont hold it down or pump just a little touch of throttle.

Ok first off to help you better understand, your engine has 4 injectors. 2 primary, 2 secondary, one of each for each rotor. Primaries are always on, secondaries are only on at 3500+ rpm.

If one of your secondary injectors is bad it will cause you to run lean (meaning engine is starving for gas, which is very bad).

The secondary injectors kick in at 3500 rpm i want to say, so if only one or both are clogged or not working properly Thats why Youre unable to reach high rpm.

First check the connections on them, the secondaries are one top of the intake manifold so they're pretty easy check.

You can also check to see if its bad with a multimeter by checking the reading it gives.

If its clogged it needs cleaned, if its simply bad and not getting the proper voltage it needs to be replaced.

Best bet is to have any used injectors you buy cleaned and flow tested before use to get maximum potential out of them.

Youll want injectors from a 89-91 na.

The primary injectors are what gets the car started.


Other things to consider.

Vacuum leaks?-- Does it ever backfire? (vacuum leaks can cause that and make it hard for the car to rev high)

Does the fuel filter need to be replaced? If Thats clogged it could cause problems with starting your car and running lean because its nit letting the proper amount of gas through it.

It does backfire alot. anytime really getting into it over 4k it backfires. how to i go about checking it for a vacuum leak? i checked connections. i had a buddy hook me up with 2 injectors that are flow tested so tomorrow Im throwing them in and see how that goes. fuel filter is brand new. thanks for explanation its exactly what i wanted to know.

To check for vacuum leaks you'll want to buy some starter fluid.

While the car is running you'll spray it around the engine and if the engine's idle goes up\engine revs up that's where the leak is.

Another thing that's always good to check is the throttle position sensor. If that's adjustment is way off or if its simply not working properly it can cause a lot of backfire on deceleration.

Mine had a corroded connection with a bunch of blue gunk on it so it wasn't even working until I fixed it. Tps on a s4 86-88 goes from 1-25% throttle then after 25% gives 100%. So if its not working right it'll give you the wrong amount of gas.

Another thing to do if you get a hesitation at 4k rpm is redo the grounds on the engine, bad grounds can cause it.

You're welcome for all the help, it's hard to get help from anyone knowledgeable on these cars. I had one for 6 years I learned a lot.

Now could the tps cause this? I recently removed my intake, did gaskets and omp lines and did a primative flow tested injectors. (hooked fuel cleaner to rails and individually opened injectors how long I wanted them open and closed to clean them) I have yet to re-adjust tps now that i've fixed my extreme intake leaks. Warm idle is around 750. My tps at idle is 2.5K and full open is 4.9K. There isnt enough adjustment in the throttle plate to make the tps read 1.0K at idle like fc3spro says. I read through their review on that. However im thinking it's injectors tho. I noticed prior to this repair i was fine 2k-7k rpm but under 2k the car had a grumble or groan. It also had a 3800 hesitation. After doing the intake I noticed the injectors have the same numbers and ohm readings so i swapped secondary and primaries since they all sprayed. Now the car runs BEUTIFULLY under 2k. No more groan but bucks over 6k. I know the injectors can spray but i cant produce a m/s pulse width they need to fire. One could be sticking at high pulse.

^Are you testing the TPS for resistance w/the car idling or w/the plug disconnected and the engine fully warmed.

Car wasnt fully warm. Ill try that and recheck. Didnt think heat would effect tps that much

Whether you set the TPS using the resistance method or the voltage method the engine needs to be as warm as it will get. W/the resistance method you need to unplug the TPS then set it, w/the voltage method the TPS is not unplugged and the key must be turned to the on position.