Engine runs uneven on all rpms

Doktor-t · 06-30-06, 05:56 PM

Regarding my 1988 Corvette with almost stock 350 TPI and auto tranny. It has about 45000 miles on the meter.

My engine runs uneven on all rpms, almost like it doesn´t fire on all cylinders every time. It doesn´t shake as much as then a engine only runs on 7 cylinders but on idle you can feel a light vibration just by touching the car.

If I run the engine steady on 1500 rpms you can hear from the exhaust that i misses now and then. (Even my girlfriend comment that it doesn´t run clean!

)

For now I have changed the sparkplugs for new ones (sparkplugs looked good), measured the injectors ohm numbers and they all is 16,9 to 17,0 ohms. New oxygen sensor. I´ve played around some with the fuelpressure regulator but nothing has improved the condition. The distributorcap and rotor looks good and the cap only had a small amount of white oxide build-up on the points. I sanded the points clean. Ignition timeing has been adjusted too but without any result. EGR-valve is replaced with a new one. I cannot find any vacuum/vaacum leaks either. I´ve adjusted the TPS to 0,54 volts. I´ve cleaned the TB and IAC.

So, tomorrow I will try to change the plugwires one by one to see if that cures the problem. If the gray "supression" plugwires are stock they might be the stock ones ´cos they do look a bit old.

Help me out guys, don´t really know what to do next

Yours: Tobias, Sweden

Vettefan87 · 06-30-06, 07:36 PM

My car did this after we did headers. What happened was we crossed two plug wires. my car actually shot flames out the exhaust. Cool affect, but the car ran terrible.

In your case the wires sound like a good place to start. If those are indeed the originals I would upgrade the distributor cap, rotor, and coil. Then you will have a complete tune up and now where to go to next if it doesn't fix the problem.

Doktor-t · 07-01-06, 12:18 PM

Okey, time for a update.

I mesured all plugwires and they all measured between 6-11 ohms. I had the ohm meter set at 20k.

I tried with a different ignitioncoil but without any improvment.

As a reference I measured a MSD 8 mm solid core wire that I had laying around and it measured 2,5 ohms.

It indeed differs when comparing the stock wires and the MSD. Do you guys think my wires on the car is bad enough to make the car run bad?

What would be the next point to aim my investigation? Valves?

This is a real P.I.T.A! I´ve started to hate my car so bad...

LT4man · 07-01-06, 12:50 PM

The nice thing about the C4s is the limited amount of parts that can be giving you a problem. Sounds like you have already replaced almost all of them.

If your ignition wires are original, time to put on some new ones.

Go to http://www.magnecore.com and learn everything you always wanted to know about ignition wires, but were afraid to ask!

Then call http://www.lingenfelter.com and order a new set of Magnecore Ignition Wires. They will give you a great price and ship them out the same day!

You can purchase them direct from Magnecore but you will end up paying full list price. Lingenfelter is a distributor.

SAVE THE WAVE!

c4c5specialist · 07-01-06, 12:54 PM

Hi there,
I would also measure the resistance of the fuel injectors.
16.5 ohms + - 1.0 ohm.
Allthebest, c4c5

Doktor-t · 07-01-06, 12:59 PM

Fuelinjectors all measure 16,9-17,0 ohms.

Tobias

c4c5specialist · 07-01-06, 02:48 PM

HI there,
I would suggest next is a compression test to confirm that all cylinders are creating equal power.
Allthebest, c4c5

geekinavette · 07-01-06, 11:15 PM

What C4C5 said....

I might also throw a timing light on it (don't forget to bypass the EST!)

Bill

G Winter · 07-02-06, 09:04 AM

You might want to check and see if you have a cat or cats beginning to plug.
Could even be one broken inside that the pieces are floating around.This could cause differences in back preasure causing a diff. in the way it runs.

Glenn

Vettefan87 · 07-02-06, 09:34 PM

What about the fuel filter

LT4man · 07-02-06, 10:27 PM

Quote:

Originally Posted by Vettefan87

What about the fuel filter

I don't know! 18 year old car. 45,000 miles. Do you think a new fuel filter would be in order?

The FSM states that you should change the filter when it is clogged! No kidding! Well, at least my 96 FSM says that!

I would think this would be a very good preventative course of maintenance!

If your filter has never been changed, now is a great time to do it.

SAVE THE WAVE!

Vettefan87 · 07-02-06, 10:34 PM

Quote:

Originally Posted by lt4man

I don't know! 8 year old car. 45,000 miles. Do you think a new fuel filter would be in order?

Um...his car is 18 years old, and since it only has 45,000 miles thats only 2500 miles a years so the car has sat a lot. With it sitting so long there might have been some sludge in his tank and clog the filter.

Doktor-t · 07-04-06, 05:39 PM

Regarding that my car has been sittin´around and havn´t been used very much is true and I think you might be on to something.

But I do got some news for you all, my neighbour came over yesterday when I was working on the Vette and when I told him it didn´t run even he told me that he works for Bosch!

He told me to fire it up and then he put a finger for a couple of seconds at each injector. He said, -These two probably got a problem, they might be jammed. He then told me to feel the tick in the injectors when they open and close and two of them felt very weak. The tick was not by far as strong as the other six. And guess what, these two injectors are both positioned on the passengerside cylinderbank! Since the car got a true dual exhaust system (sounds bad from passengerside exhaustpipe) I know for sure that the problem is located at the passengerside, same as the weak ticking injectors.

My neighbour thought that they might have jammed because of the car havn´t been used regulary, possible?

Can this be the thing that cause the uneven running?

By the way, the fuelfilter, if that would be clogged, the car wouldn´t run very well at full throttle would it? The car does however run very strong at full throttle and it actually did (measured with G-Tech) a 0-60 mph in 5,4 seconds when I tested it uphill! That´s pretty good for almost stock, isn´t it?

Thankfull for all help; Tobias

Vettefan87 · 07-04-06, 09:35 PM

Quote:

Originally Posted by Doktor-t

My engine runs uneven on all rpms...

You said this in your first post...

Quote:

Originally Posted by Doktor-t

By the way, the fuelfilter, if that would be clogged, the car wouldn´t run very well at full throttle would it? The car does however run very strong at full throttle...

Then you said that so I am a little confused now... If you had two injectors that were not working properly I find it very hard to believe it would run good at WOT.

I would think if your fuel filter was partially clogged or there was some sediment in it it wouldn't run very good....But you said it runs great at WOT.

MoeJr · 07-04-06, 11:34 PM

Get yourself a can of BG 44K fuel system cleaner and dump it into the vette when the car has 3/4- full tank of gas and see if that clears it up.And by all means if you haven't changed the fuel filter in the last 10k miles then do it.

BG website is www.bgprod.com