1986 s4 na wont go past 3,000rpm??
 

i have a 1986 s4 na that worked perfectly before but it had a exhaust leak so i got that fixed and after a few days of that getting fixed my car lost power and now it wont go past 3,000rpm. the exhaust leak was by the downpipe. car got stucked for about 2 weeks cause of bad flooding then finally got it running again but still has the same problem. it runs and its driveable shifts and everything i just cant go past 3,000rpm or it starts sputtering.

i replaced the spark plugs/wires, mass airflow meter, the tps and also the ecu. (ecu had 2 fryed resistors).
i also talked to a couple of people and they gave me advice to replace some parts,
oil metering pump, bad engine harness grounds, and ofcourse the secondary fuel injectors, i had someone test out the secondary injectors and theyre still pretty good.

the car also idles at 1,500 goes down and goes up.

Check the tps plug for corrosion. My engine was acting up not wanting to go past 2000rpm, and the tps was good, but the plug was corroded. So if you are lucky it could be that simple.

Have you checked for vacuum leaks? pressure sensor?

Why would changing the omp help anything?

check all of your grounds in the engine bay. buddy of mine had an S4, did the same thing, we spent like 4 hours replacing all of the grounds and cleaning up where they go with a little sand paper. Fixed it right up. Good luck!

I stopped by to help with this S4 a few times over the past 2 weeks.

It isn't sputtering...around 3k-3.5k it hits a brick wall at WOT.

It idles at 1.5k unless I go after the linkages to the thermowax, then it sits around 750 until the throttle is touched.

TPS was replaced with another one and set with 2 test lights. His original one needed the adjustment screw cranked all the way closed. I was able to a loosen the screw a bit with the replacement one.

Also tried to pull some codes off the diagnostic connector. Nothing noticeable came up.

I didn't check the grounds (trans->firewall or the ring terminal in the rat's nest). I didn't see any reason for the shop to mess with those to fix a downpipe. :/


To OP:

Get that can of starter fluid, dammit! XD If you have a propane blowtorch you can use that too, just don't light it. Aim it around the intake and listen for the engine to change tone or smooth out.

Did you ever talk to the shop to see what they touched?

ill try and see if i can borrow a propane blow torch. but i have some starter fluid. just havent sprayed any yet.

If your exhaust is original, the 26 year old catalytic converter should be suspicious at this point...

I don't see the OMP as an issue here. Cross that off your list.

Grounds grounds grounds. I have an 87 s4 that had the same idle issue and it hit a wall just after 3k. Pull the UIM off and clean/replace the grounds. Scratch all the paint where the grounds meet the body and sand all other contact points. We even added some grounds directly from the ecu to the passenger side floor board in order to trick the ecu into thinking its grounded all time.

sorry for old bump but i have similar problem with the 87 s4 i just bought today its bouncing all over the place at idle and when you go to slam the throttle it wants to die if you let off it will back fire if you hold it like 1/4 to 1/2 throttle it will rev up some what smooth but still rough idk what to think....

make sure your 6 ports are working

for sure but would that make it so when idling the engine is bouncing around like its missfiring or non stop firing?

6th ports won't efect the idle like that. Have you done a tune up? Spark plugs, ignition wired, etc?

nope guna do it monday but ill get back to you guys after its done

See what that does and get back to us

Did I just repeat everything you just said? Lack of sleep...

Clogged cat(s) probably caused your exhaust leak. You fixed the leak, now the exhaust has nowhere to go.

Could be a lot of things. Make sure your fuel filter is replaced. Check grounds. Check the catalytic converter. Make sure you have no busted vac lines. Check TPS.

i know where the exhaust leak is its after the cats its where some dumb a didnt know how to weld and just globbed it up and it broke lose.

for sure

My old S5 would hit a wall at around 3k, had to pull off and let it sit for about 20 minutes at times. My fuel filter was clogging up.

When my 88 exuded the same symptoms as the OP, both my pre-cats were melted and clogged.

would the plugs still be fouled looking if the fuel filter was clogged?

so if i were to cut my cat off would it stop the problem? the exhaust is broken off right after it anyways so....


today i checked the timing and it the leading and trailing was on the same mark idk where the vacuum advance is if there is one... and i could turn the crank pully by hand. bad right?

and sorry about not knowing the info on vacuum advance i know more about 12a...

Just unbolt it and look into it. No need to cut it off. Do you have any pre-cats? Check those first.

Are you sure they were on the same mark? One should be yellow and one should be red. If the marks have the color worn off, they look the same. Stick some nail polish on them (different colors obviously) and try again.

How far did you turn the pulley? I can turn mine up to compression, then no.

first
just have 1 cat on it and i didnt pull it yet

second
a full rotation
and i can see the the other mark with the timing light

and update
i put new plugs and wires it stabilized the idle so it wasnt as bad
and i had my buddy put his and over the mass airflow jerry rigged opening there is like a gap on the bottom where someone tryed to bolt up a 3" adapter to the square and yeah you get it and it ran perfect with his had over the 3" opening and the gap open im trying to get a mass airflow on there and see if it fixes it(i poped the top off the mass airflow and some one messed with the settings and stuffs so i think thats the main problem and not only that i think the gap underneath might have sucked water up in and fried it so...)