missing under load under 2k

[mlotruglio]

Ok so I think I no what my answer is going to be besides big money, but I want to ask any way. I have a miss when my car is under load below 2k-ish on the tach. It felt a lot like a bad plug wire. So I replaced the plugs, and wires, no fix. Then coils, I blew a vacuum line so I had to pull the plenum anyway, nothing. Next checked the fuel pressure and delivery, perfect, and I replaced the fuel filter. Then I cleaned the fuel rail and injectors with 3ms aerosol cleaner (run the car off the cleaner) and added the fuel additive like 3m says. Then map sensor, lastly throttle position sensor. Nothing has worked. A lot of the stuff needed to be done; my car was sitting for the better part of 2 years before I bought it. I think at this point I need to suck it up and buy some new injectors. Dose any body have any ideas?

[ZZZZZR1]

Originally Posted by mlotruglio

Ok so I think I no what my answer is going to be besides big money, but I want to ask any way. I have a miss when my car is under load below 2k-ish on the tach. It felt a lot like a bad plug wire. So I replaced the plugs, and wires, no fix. Then coils, I blew a vacuum line so I had to pull the plenum anyway, nothing. Next checked the fuel pressure and delivery, perfect, and I replaced the fuel filter. Then I cleaned the fuel rail and injectors with 3ms aerosol cleaner (run the car off the cleaner) and added the fuel additive like 3m says. Then map sensor, lastly throttle position sensor. Nothing has worked. A lot of the stuff needed to be done; my car was sitting for the better part of 2 years before I bought it. I think at this point I need to suck it up and buy some new injectors. Dose any body have any ideas?

Absolutely Injectors... Do you think they were original?

If they are original, that is probably your issue. I'd recommend FIC (new Stainless Steel ones), but there are a few makers of injectors.



David

[LGAFF]

check your 2ndry map sensor?

[Kevin]

year/miles? i'm willing to bet it's injectors

[mlotruglio]

1991 with 61k It has injectors with rc red and white stickers on them. im guessing that means there after market. Ive never heard of a seconday map. I no the car has a map and a altitude sensor but a secondary map....do tell (location)

[tomtom72]

Under the ECM bracket is where the 2* MAP is located. There is a vacuum line comes in from the rear of the plenum and crosses over by the master cylinder for the brakes, and goes under the ECM bracket.

I'm not so sure on this.....do you get any SES lights when the miss happens? Is the miss constant? What happens to the miss if you drive in "Valet" mode, Full Power off/on? Does the miss happen at idle speed? When hot only? When cold? Can you smell the exhaust, is it lean or rich? Have you tried to use a scan tool to see what the fuel numbers are doing?

Yes, the injectors have already been replaced. RC's are/were one of the only reliable choices farther back than about 5 yrs ago. It's unlikely but it could be one of the primary injectors have broken down.....usually this doesn't happen with the RC's.


Tom

[A26B]

Matt,

A cost-nothing test.

One of the tests that will expose a weak spark problem is to put the engine under load at a low rpm, usually in 6th gear from about 45~50 mph & gradually accelerate. Very much like you described. Weak spark miss is disguised at higher rpm, although it does affect engine performance significantly.

I suggest that you re-visit coils & wires. Pull the plug wire from one plug at a time, install an old plug in the wire and lay it on the plenum. Start the engine & gradually pull the plug away to cause the spark to jump. A blue spark about 3/4" long is good. If you have an orange spark, it's weak.

It's best to do this in the shade to see the spark better. Note the spark condition of each cylinder. Having weak spark on one cylinder only does not necessarily rule out a coil.

I also recommend using silicone grease (dielectric) on each end of the plug wire boot and on the coil terminal. They seal better and resist moisture better which can also cause a miss.

[mlotruglio]

My shop manual and parts book say that is the altitude sensor. Im going to have to look deeper in that. I have no lights, and it never really goes away Full power and Normal Power both miss, I have not heard it at idle ( cant feel it) Dont think so though Hot cold same The exhuast smells right. As far as a scan tool I have a obd 2 but That dose not help me.
Its really stumping me

Originally Posted by tomtom72

Under the ECM bracket is where the 2* MAP is located. There is a vacuum line comes in from the rear of the plenum and crosses over by the master cylinder for the brakes, and goes under the ECM bracket.

I'm not so sure on this.....do you get any SES lights when the miss happens? Is the miss constant? What happens to the miss if you drive in "Valet" mode, Full Power off/on? Does the miss happen at idle speed? When hot only? When cold? Can you smell the exhaust, is it lean or rich? Have you tried to use a scan tool to see what the fuel numbers are doing?

Yes, the injectors have already been replaced. RC's are/were one of the only reliable choices farther back than about 5 yrs ago. It's unlikely but it could be one of the primary injectors have broken down.....usually this doesn't happen with the RC's.


Tom

[mlotruglio]

I have never had much luck with testing by pulling off the wires but now that you gave a color and size Im going to try it I will get back to you !!!


Thanks!!!!=D>

Originally Posted by A26B

Matt,

A cost-nothing test.

One of the tests that will expose a weak spark problem is to put the engine under load at a low rpm, usually in 6th gear from about 45~50 mph & gradually accelerate. Very much like you described. Weak spark miss is disguised at higher rpm, although it does affect engine performance significantly.

I suggest that you re-visit coils & wires. Pull the plug wire from one plug at a time, install an old plug in the wire and lay it on the plenum. Start the engine & gradually pull the plug away to cause the spark to jump. A blue spark about 3/4" long is good. If you have an orange spark, it's weak.

It's best to do this in the shade to see the spark better. Note the spark condition of each cylinder. Having weak spark on one cylinder only does not necessarily rule out a coil.

I also recommend using silicone grease (dielectric) on each end of the plug wire boot and on the coil terminal. They seal better and resist moisture better which can also cause a miss.

[lbszr]

Originally Posted by mlotruglio

My shop manual and parts book say that is the altitude sensor. Im going to have to look deeper in that. I have no lights, and it never really goes away Full power and Normal Power both miss, I have not heard it at idle ( cant feel it) Dont think so though Hot cold same The exhuast smells right. As far as a scan tool I have a obd 2 but That dose not help me.
Its really stumping me

The sensor under the ecm senses when there is vaccum to the secondaries and tells the ecm what is going on, incase there is a descrepency of the secondary position. I believe there is only ambient pressure to this sensor below 2000 rpm normally and since you have no codes, I wouldn't be looking there.

It does sound like ignition as mentioned previously. I've had multiple coil problems, but mine missed intermittently at idle also.

Have you ohmed the injectors? Or you could swap the primaries with the secondaries to see if the problem stops, if the RC's are the same? Lotta labor, but labors cheap.....right?