1988 S4 NA, rebuilt engine everything stock, no leaks, idling is stable. Car stumbles on 2nd and 3rd gear. Feels like somebody is choking the car and doesn't want to let it go.
Things that I did and checked. I started with TPS (good 1 volt and counter checked by using two led lights, only one illuminated). Checked-timing and CAS, Checked BAC (removed-cleaned and adjusted). Variable Resistor adjusted (Richer) for best possible idling. Idle mixture on top of dynamic chamber screwed all the way in because if I put a little air idling gets higher. While I am doing all these adjustments green connector is grounded.
Please help what else am I missing.

Thanks,
EJO

 

At what rpm is the car stumbling?

 

WOT- 3K and above.

 

Secondary injectors come online at 3800 rpm. The TPS releases fully from the throttle linkage at around 3000 rpm.

 

I got all my injectors reconditioned by RC engineering, each one of them passed their testing. Can you please guide me what to do next? A more detailed explanation how to tests and make sure that the things that you have mentioned works properly. Thanks a lot.

 

Does the stumble occur precisely at 3000 rpm and above or is that a ball park figure? Can you rev the car in neutral and encounter no stumble?

 

Go over the ignition system. Clean the grounds on both the Leading and Trailing coils.

After that check the condition of your plug wires. Check for arching at night.

Also one thing that happened to me make sure the leading and trailing wires are separate from one another.

Lemme know what happens.

 

@ Satch- Yes I can rev the car without stumbling, and also yes on the 3K-ish and above rpm when it starts stumbling.
@ Leonel 95- I will definitely follow your instructions. When you say "arching" at night are you referring to check if I can see spark at the wires if it's dark. I will definitely inform you all what happens next. Thanks for responding.

 

Try unplugging the TPS and see if it makes a difference.

 

I discovered where the problem is Satch. Only one Auxillary port is activating when I rev the engine above 3800 rpm and above. I'll try to remove the UIM and LIM manifold this week-end and check if that will solve the bogging or stumbling of my car. Cross my fingers. Thanks for sharing all your expertise. Forum rocks!

 

what is the 'UIM and LIM' manifold? my car is running just like how you are describing it. There's no get-up at all. As soon as I hit 3k it gets worse starts jerking real bad.

 

UIM- upper intake manifold
LIM- lower intake manifold

 

to be able to reach, check and clean the auxillary port sleeve we need to remove them all. It's a PITA but we need to do it. Best time to get your injectors reconditioned, vacuum lines upgrade to silicone etc. etc. Hope it helps.

 

help! I used a "noid" testing light and found out that both of my secondary injector wiring is not sending the electrical pulse needed to activate my injectors above the 3800 rpm. What and where should I start to fix my problem. Thanks a lot.

 

The secondary injectors wont turn on if you rev the car while in neutral in a normal situation because there is no load on the engine and this prevents the ECU from using them. So you need to unplug the TPS and remove the vacuum hose from the Pressure Sensor to create load while in neutral so as to trick the ECU into turning on the secondaries above 3800 rpm. And the pulse is a ground signal.

 

Satch is right, we chased a problem for months and couldn't get our car to run at WOT. Did all the normal things on grounds etc. My bet would be the secondary injector clip is broken. It is very hard to tell if it is good or not. My suggestion would be to purchase new clips and wire them in. This would take less than a half an hour and is pretty easy to do.

Fixed our car and she has run like a champ since.

 

@Satch after following your instructions the noid started blinking, process of elimination I guess the wire is good and sending the signal. One less things to check. What would be my next move?
@oldshooljoe I will try your recommendation, any particular place of your choice where I should get my injector clips? Thanks for your patience and help, I am not quitting yet for my quest to gain that lost HP on my car. Please bear with me.

 

You mentioned that one of your 5th and 6th ports were stuck. Did you fix this? Does your stumble occur at various rpm's or at the 3800 level when the secondaries kick in?

 

Satch I wasn't able to fix my auxillary port, here's what I did, put a wire on my 5th & 6th port and left it on assuming that if I left it open I can check during high load or rpm if car will l accelerate more sacrificing low end hp. But that didn't change anything so what I did is started reading the forums and found out that if your secondary injectors are not working you won't be able to pass the 3800 and above rpm. Also, I bought a stethoscope and tried to probe my injectors and couldn't hear any clicking sound I was doing this while at load.

 

You can go past the 3800 level but it will stumble at that point until the secondaries eventually kick in so the question still elludes us, what rpm range is your car stumbling at? You can pull the injector plugs and look to see if the wires are pulled back in the plug. If this occurs then it won't mate well w/the injector.

 

car stumbles at 2nd & 3rd gear at 4500 and beyond K RPM. Can't get that power that I am looking for. I have played with my injector clips, pulled, cleaned, checked looks good. They're in decent condition even used magnifying glass to check clearly inside if the connectors are missing something. What I am planning to do next is follow FSM instruction of pulling it out, wire them on it's rail, jump on that fuel primer connector, switch it on and check if it will squirt fuel ( I guess for clogging or something else). What do you think? Thanks

 

It's somewhat easy to check the primary injectors but harder to check the secondaries because I'm not sure you can spin the CAS fast enough to activate the secondary injectors even if the car was under load. You could place a ground on the ECU trigger wire for each of the secondary injectors to at least check it in that manner. Not too familiar how a troubled stuck port affects your car but your problem could be caused by other things such as a clogged cat or weak fuel delivery or even the Pressure Semsor. You could drive the car w/the vacuum hose to that sensor disconnected and plugged. And if that doesn't change things then also in addition disconnect the TPS plug.

 

my car has a similar issue. It stumbles over 3500. Gets worse closer to 5 and 6k rpm. Doesnt do this in neutral no load. Im thinking secondaries. This started after i replaced my upper and lower intake gaskets, lines, omp lines etc. I replaced the crumbled injector connectors but still no good. My questions are: What drivability effects can I expect unplugging TPS to test? Also does the engine have to be warmed up to test it? Does heat have THAT much of an effect on the readings in the TPS

 

You can place the engine under load as suggested in this thread and rev the car to check things. You might want to check your grounds as the main ground was likely messed w/when you replaced your manifold gaskets or the secondary injector plug(s) connection is below standards.. And if your car is an S5 you should check for error codes?

 

One last question before I burn my car, is there any connections inside my dashboard that will affect my secondary injectors not to activate? as of now I don't have a dashboard and just a few electrical connections are connected, speedometer gauge, headlights that's about it the rest are all unplugged. I will get it painted as soon as I solve this horrible problem of mine. Help my boat is sinking......