aw3375

I have a 1990 with the L98 engine. It started running rough when cold but would smooth out after a couple miles down the road. Then it started running rough all of the time. I changed the plugs, wires, dist. cap and rotor and nothing changed. the car still runs very rough and shakes. When accelerating, it lacks power and shakes bad. It feels and sounds like the exhaust is hitting the floor. Any Ideas would be great. Thanks.

MyFirst90coupe

Might be the injectors. Get an ohmeter and test them.

aw3375

All of the injectors tested around 16 ohms cold and 17 ohms hot. All were within .5 ohms of each other.

aw3375

This seems kind of strange to me but I had the car running and I took the cap off of the coolant tank and the car started running smoother. I put the cap back on and took the car for a drive and it still runs a little rough at low speeds but it gets up to 55 fine and seems to run smooth until trying to accelerate or until slowing down.

CorvetteMike2024

That doesn't tell you if the injectors are plugged.

ZR1 NABE

Hey !!

I have sort of the same problem now..... I decided one sunny morning to wash my engine and degrease it, then after it was rinsed I turn on the car and it was running like if it only had 7 cyl. then I hear my cats banging like I hit a rock .... now it just runs rough , I checked every wire under the hood and nothing.

but the best part to this Davinci code is that ... there are NO CODES on the Dash.

Please help.

gmboileau

Any codes? With the engine running so badly you would think that it would trip a code.

A no power situation could trigger a Code 44 ......lean code.... could be caused by blocked injectors..vacuum leaks...blocked fuel filter

ZR1 NABE

very true ,but there are no codes..... It aches me to see my vette just sitting on the driveway because I doesnt run right .... because of a f..ing motor wash!!!

capici?

esham

You may want to start your own thread......but I suspect you got your optispark wet.

Mikes1991

Hmmmm dont feel to bad. I changed my coolant on a 100 degree day and blew my head gasket. Ill make sure not to wash my motor now lol Probably the opti spark yep

Mikes1991

What about the exhaust could be clogged cats or bad oxygen sensor that doesnt send a code

gmboileau

Several items that can cause a engine to run rough/no power without codes...some items that come to mind are


- bad/shorting ignition wire
-blocked cat
-firing order mixed up
-EGR valve stuck in open position
-timing way off...stetched or jumped timing chain
-vacuum lines misrouted/split or off
-head gasket/cracks leak

This is far from a complete list....I guess the only thing to do is to eliminate the possibilities by using the test procedures in the FSM.

To complicate the issue further some Codes will only set if certain operational conditions are met. For example, some codes will only set if the engine is above a certain RPM and is in Closed loop.

These problems can be a real pain.

aw3375

I thought about that too. Is there a way to check if the cats are clogged without removing them?

j-wireman

He said he has an L98. No Optispark there.


"..feels...like the exhaust is hitting the floor..."----Could that be caused by a broken motor mount or loose exhaust hanger? I don't know.

esham

I know the OP has an L98. My response was to ZR1 NABE who has a 1994 LT1 that started having problems after he washed his engine.

walter schweigert

There may be a way to measure back pressure by removing the o2 sensor and attaching a pressure gauge. Don't know what the reading should be though.

Do you have access to a scan tool that can monitor data? If you can get a hold on one, some of the information it could provide may be helpful.

MyFirst90coupe

I wonder if that indicates a head leak where when it's under pressure it's pushing coolant into the cylinder.

aw3375

I started pulling the wires off of the injectors while the engine was running and there is no change when I pull them from cylinder 2 and 5. I am thinking they are just plugged. When I check them with an ohm meter they test at 17.2 ohms. They all range between 16.8 and 17.2. I was told that the dealer has an engine vac that runs 4 different cleaners and lubricants through the fuel rails and will clear any clogged injectors. Any opinions?

Thanks.

CorvetteMike2024

on my last injector change out, I had 2 injectors plugged.

Watch FIC's thread in the C4 tech sticky

http://forums.corvetteforum.com/c4-t...questions.html

kenv

That`l do it