shudder after 5lbs boost FIXED!

anthrax

Registered User
whenever i give it alot of gas and the boost hits 5lbs boost the car shudders and feels like its gonna die dosesnt matter if its off the line or cruising. the car drives 100% fine under 5lbs. right before this happened the air intake fell off driving home. its a 90 sc auto with about 150xxx miles
 
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Sounds like...

whenever i give it alot of gas and the boost hits 5lbs boost the car shudders and feels like its gonna die dosesnt matter if its off the line or cruising. the car drives 100% fine under 5lbs. right before this happened the air intake fell off driving home. its a 90 sc auto with about 150xxx miles

I had a similar issue in a 35th Anniv. that I had once. Once of a couple things to check.

First, replace the plugs and wires with either Autolite 8mm or Taylor 8mm wires. For plugs, I have found in the past that a standard Autolite or Autolite Double Platinum work the best. You do not want to skimp out and go cheap in this area, or you WILL be doing it twice, trust me!

Second, search for vacuum leaks. Under boost, these will become boost leaks, but usually will just limit boost and not cause the stumble that you have. Check all vacuum lines and clamps on all piping. Also, if so inclined, reseal your IC tubes.

Does your check engine light come on? Have you pulled and check for codes?
 
i dont get a check engine light. i havnt had my IC tubes off in months. i hear a very high pitch whistle close to 5lbs so i probably have a vacuum leak. so that makes sense. oh idk if this has anything to do with it but the check gauge light is on and the tach works and then stops and works again. all the other gauges are fine. i swapped my tach with a buddies and same problem. maybe crank position sensor?
 
Check for codes anyway....

i dont get a check engine light. i havnt had my IC tubes off in months. i hear a very high pitch whistle close to 5lbs so i probably have a vacuum leak. so that makes sense. oh idk if this has anything to do with it but the check gauge light is on and the tach works and then stops and works again. all the other gauges are fine. i swapped my tach with a buddies and same problem. maybe crank position sensor?

That tacometer dropping out could also be, possible, the ignition module, but is more likely the cam sensor. Check them codes even with no CEL light. Do all the tests, KOEO, Continuous memory, and KOER, then finally the Cylinder Balance test. But the code scanner, it help alot. Pay very close attention to the Continuous Memory codes. Not all the time does a code cause the CEL to come on and stay on, especially intermittent problems.
 
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i know how to do the KOEO and KOER tests with a jumper. i dont have the scan tool. and whats a cylinder balance test? and is there a way to test the cam sensor with a volt meter?
 
haha very true. ill try that. i got a list of stuff to do on it but its been raining so its been delayed -_-
 
Yeah cam sensor

I also have 90 auto. Had similar prob at about 98k. Tach acting up is the giveaway. Cam sensor's a magnetic device so may test ok but still be intermittent. Also be aware these cars (90's) are OBD ONE so very hard to find AFFORDABLE code scanners.
 
so i looked outside and saw 2 of my vacuum hoses were almost melted. and i hoseclamped them on. i took off to the store and when im pulling in the lot the car gets real choppy but still runs and drives. i park and i see my coolant temp is a bit high so i added some water and let the car cool down and started it back up and still continued. i drove the car home and parked it and opened the hood with the engine running and saw that the supercharger was being bypassed. and the engine was real hot. i mean like when you open an oven. birds always run hot but i touched the sc outlet and it was scalding hot. any ideas?
 
Also be aware these cars (90's) are OBD ONE so very hard to find AFFORDABLE code scanners.
Mine is quite affordable.. I use a paper clip, a pencil, and notepad! OK, so I got sophisticated and crimped a couple of fork tabs onto a 2" length of wire.. but you get the idea. :D
 
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ok enough with scanners. back on topic. did the koeo and got nothing koer was hard. the engine wouldnt stay running but when it finally did the MAL lamp blinked 3 times and then idled real high like 1200-1400 rpms
 
I had a similar problem---it would run like a dream until I got into boost and then it would miss like a pig.....I hate to admit what it turned out to be because it took me a whole day to find it but I had a sparkplug wire not completely seated. The boot was on the plug but the wire was not snapped onto the plug. ...............Dan
 
ok i have pulled the whole harness off and checked for bad wires and taped it back up. nothing. i tightened the screws on the DIS and the coil pack. nothing. i reseated the plug wires. nothing. i checked to see if the spark plug wires were right. nothing. i checked the IC tubes. nothing. i checked to see if i have fuel in the fuel rail and i do. im starting to get frustrated and ran out of ideas. someone help before i go crazy
 
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i hear a very high pitch whistle close to 5lbs so i probably have a vacuum leak.
There's your likely problem. There are a number of vacc lines on the back of the TB. You should check them all out. I had a rubber hose that was hooked up to the line that goes to the purge canister that had crumbled causing a vacc leak. I heard the "wheeze" whenever I turned the engine off.
the tach works and then stops and works again. all the other gauges are fine. i swapped my tach with a buddies and same problem. maybe crank position sensor?
This happens often. If you have a new cam sensor, then swap out the DIS for a new/known working one.

Oh, and on the subject of plug wires. I had a stumble under boost problem. After swapping the DIS, fixing vacc leaks, installing a new fuel filter, and new FPR, I installed new plug wires. That seemed to be the biggest problem as the othir thing I did seemed to improve how it ran. Here's the big note however... when you push the plug wire onto the spark plug, it must SEAT with a click/snap/whatever. You usually have to push so hard that it hurts your hand to get it right. If you're not swearing about it and you don't have scrapes all over your arm and hands when you're done, you probably didn't get it. :rolleyes:
 
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