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]

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.

:cheers:

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.

:cheers:
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:mad::confused:


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.

:cheers:
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>

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]

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:mad::confused:

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?

[Tyler Townsley]

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>

Pull all plugs look to see which has a different color, if its black it could be leaking inj if its white it is too lean on that cyl again inj problem.

Tyler

[tomtom72]

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:mad::confused:

I would try looking at the plugs to see if they have anything to tell you. Also, refrain from removing a plug wire one at a time while the motor is running as the DIS box doesn't like that too much and you could damage it eventually.

On the scan tool, if you have a rather good one most offer an adapter. This adapter is a two sided connector that plugs into the OBDII connector already on the machine and it has an ODBI pattern so it can plug into an OBDI ALDL socket in the car. The only rub is you need the software for your yr Z and then you can run diagnostics. Do you by chance have a snap-on MT-2500? If yes I could lend you my software ( I'll have to check if it goes to 91 ) and my OBDII to OBDI adapter plug.

Okay, I should read more carefully!:o Since the miss is constant in either full or normal, and you have no SES light ( even briefly like it's winking at you ) and you changed the coils & wires & plugs and the exhaust doesn't smell lean or rich.....the work that was done was done after it sat for two yrs: plugs, wires & coils? You didn't notice any evidence of mice chewing any of the under plenum wiring? Did you notice any chaffing of the injector harness at the injectors ( one of our brothers found a chafed injector wire that got pinched when he put the plenum back on ) or any carbon tracking on the coil mounting block or anything out of the ordinary under there? You got that vacuum line plugged in at the lower right side of the throttle body? I'm just thinking out loud here, sorry.:o

Look at the plugs first as Tyler said and then do the spark quality test as Jerry said.

[mlotruglio]

Yes I bought her after her long "nap". My scan tool is a $300 advance auto cheepie so I can rule that out!!(:censored:) There were no mice or anything like that so I can rule that out also. A friend of mine found a way to test the injector coils with out pulling the plunum so Im going to try that and I am deff going to pull the plugs and see if I can get any clues there. Im also going to trow in a twist now to Before I filled up that other day I added a bottle of octane booster($2 for kicks and giggles) she had about 2-3 gallons left and It was almost perfect. soooo IDK. Tomarrow I will pull the plugs, and if I have time I will run the injector coil test.


I would try looking at the plugs to see if they have anything to tell you. Also, refrain from removing a plug wire one at a time while the motor is running as the DIS box doesn't like that too much and you could damage it eventually.

On the scan tool, if you have a rather good one most offer an adapter. This adapter is a two sided connector that plugs into the OBDII connector already on the machine and it has an ODBI pattern so it can plug into an OBDI ALDL socket in the car. The only rub is you need the software for your yr Z and then you can run diagnostics. Do you by chance have a snap-on MT-2500? If yes I could lend you my software ( I'll have to check if it goes to 91 ) and my OBDII to OBDI adapter plug.

Okay, I should read more carefully!:o Since the miss is constant in either full or normal, and you have no SES light ( even briefly like it's winking at you ) and you changed the coils & wires & plugs and the exhaust doesn't smell lean or rich.....the work that was done was done after it sat for two yrs: plugs, wires & coils? You didn't notice any evidence of mice chewing any of the under plenum wiring? Did you notice any chaffing of the injector harness at the injectors ( one of our brothers found a chafed injector wire that got pinched when he put the plenum back on ) or any carbon tracking on the coil mounting block or anything out of the ordinary under there? You got that vacuum line plugged in at the lower right side of the throttle body? I'm just thinking out loud here, sorry.:o

Look at the plugs first as Tyler said and then do the spark quality test as Jerry said.

[tomtom72]

Be very careful about back probing the ECM harness plugs. You will enlarge the female end of the connector if you use something like a test light probe. Use stranded wire so you can adjust the size to get a good connection without enlarging the female terminals. This caused much tracking down of intermittent faults in another member's car! Drove him nuts for quite a while.

You might as well just check the ohms on the plug wires and coils while you have the DVOM out of the tool box. You can ohm from plug wire thru the coil to the matching plug wire....I believe it should be in the 30k to 50k ohm range.

It could be that the octane booster dislodged some crud and it's fouling the tip of an injector? I doubt that that stuff did any actual harm to any fuel system parts....it's not like you used Moroso Octane Booster concentrate...do they even make that stuff any longer?

:cheers:
Tom

[ZR1@gmx.com]

Jerry's recommendation about using silicone grease (dielectric) on each end of the plug wire boot and on the coil terminal fixed my miss that was similar, probably worse than yours.... Cheep fix!!!