2.9 rough idle and misfires at lower RPM, low power.

[JLArangerdriver]

I have a 1987 ranger 4x4 standard transmission with 59,XXX original miles. (although there's a chance it could be 150,xxx)It was well taken care of, but sat for years. It has random misfires at idle, no single cylinder is a dead miss. Same issue when driving, but down shifting, increasing the RPMs seams to fix it most all of the time. I just put in new injectors, new fuel filter, new tank and cleaned all the gunk out of the fuel rail and lines. The truck sat for about 4 years after I had replaced the injectors and filter, but not cleaned out the fuel rail, and only cleaned the rusty tank. I'm pretty sure the Truck wasn't doing this before the injectors in it when I bought it started to fail. I disabled the EGR, by disconnecting the electrical connector and capping off the plastic vacuum line, that was already broken. I assumed this would cause the EGR valve to remain closed, but is their a chance it's stuck open? The tiny plastic vacuum lines that go to the air cleaner box were broken when I got the truck. I remember it idled rough and high, but no misfires while driving. I reduced idle by turning the adjustment screw on the throttle body, I think I saw that you arn't really supposed to do it that way, but it worked. I've replaced the distributer cap, it was pretty warn, but I've seen worse still running okay. It didn't help. I can't find any vacuum leaks, the vacuum line for the MAP sensor holds vacuum... but tastes very bad, haha. I haven't done a compression test since it sat for a few years, I'll probably do that tomorrow. I have to borrow the tool. I'm between jobs right now and don't have extra cash to throw a lot of parts at it, unless I have to. I'm not the best at diagnosing 1980's EFI vehicles. The best I can figure is it's either bad MAP sensor, Idle air control unit, distributer, ignition module, O2 sensor, the EGR is stuck open, the cheaper injectors I put in it were bad ,or maybe the ECM/computer is messed up. I'm not sure how I'd even go about replacing that last one, does it need to be programed to the truck? I could probably spend a lot of money replacing all of these and with my luck lately, it still might not fix it. No oil in the coolant or coolant in the oil. I also had to solder new connectors onto the injector harness. What I'm asking is, what should I go after first, and are their ways to rule out any of these potential causes?

 

[ryan445]

I am currently chasing something similar. Currently I am at the last two possible things. Injectors or ECM. I'm gonna attempt to take out and clean the injectors. I am sure they are clogged with the 4 year old fuel I had.

If you have a code reader for the EEC-IV computer it may help you pin point something but the computer, really since it isn't that smart, it can come back all clear and still have issues.

Did you replace your fuel filter after it sat for four years? If not I would definitely start with that that. That gas was definitely lacquered after that long. Unless you had no gas in the tank and line at that time.

Do you remember what your plugs looked like when you pulled them? Did they look fouled or lean in any way? Plugs can help tell a story.

 

[PetroleumJunkie412]

I have a 1987 ranger 4x4 standard transmission with 59,XXX original miles. (although there's a chance it could be 150,xxx)It was well taken care of, but sat for years. It has random misfires at idle, no single cylinder is a dead miss. Same issue when driving, but down shifting, increasing the RPMs seams to fix it most all of the time. I just put in new injectors, new fuel filter, new tank and cleaned all the gunk out of the fuel rail and lines. The truck sat for about 4 years after I had replaced the injectors and filter, but not cleaned out the fuel rail, and only cleaned the rusty tank. I'm pretty sure the Truck wasn't doing this before the injectors in it when I bought it started to fail. I disabled the EGR, by disconnecting the electrical connector and capping off the plastic vacuum line, that was already broken. I assumed this would cause the EGR valve to remain closed, but is their a chance it's stuck open? The tiny plastic vacuum lines that go to the air cleaner box were broken when I got the truck. I remember it idled rough and high, but no misfires while driving. I reduced idle by turning the adjustment screw on the throttle body, I think I saw that you arn't really supposed to do it that way, but it worked. I've replaced the distributer cap, it was pretty warn, but I've seen worse still running okay. It didn't help. I can't find any vacuum leaks, the vacuum line for the MAP sensor holds vacuum... but tastes very bad, haha. I haven't done a compression test since it sat for a few years, I'll probably do that tomorrow. I have to borrow the tool. I'm between jobs right now and don't have extra cash to throw a lot of parts at it, unless I have to. I'm not the best at diagnosing 1980's EFI vehicles. The best I can figure is it's either bad MAP sensor, Idle air control unit, distributer, ignition module, O2 sensor, the EGR is stuck open, the cheaper injectors I put in it were bad ,or maybe the ECM/computer is messed up. I'm not sure how I'd even go about replacing that last one, does it need to be programed to the truck? I could probably spend a lot of money replacing all of these and with my luck lately, it still might not fix it. No oil in the coolant or coolant in the oil. I also had to solder new connectors onto the injector harness. What I'm asking is, what should I go after first, and are their ways to rule out any of these potential causes?

Man you have so many possible points of failure there...

Ok. One. Are you **sure** the injectors you bought are the same flow rate as the ones you took out.

 

[JLArangerdriver]

I am currently chasing something similar. Currently I am at the last two possible things. Injectors or ECM. I'm gonna attempt to take out and clean the injectors. I am sure they are clogged with the 4 year old fuel I had.

If you have a code reader for the EEC-IV computer it may help you pin point something but the computer, really since it isn't that smart, it can come back all clear and still have issues.

Did you replace your fuel filter after it sat for four years? If not I would definitely start with that that. That gas was definitely lacquered after that long. Unless you had no gas in the tank and line at that time.

Do you remember what your plugs looked like when you pulled them? Did they look fouled or lean in any way? Plugs can help tell a story.

Yes, I replaced the tank, the filter, the pick up sock, cleaned the pickup tubes, replaced the float and blew carb cleaner through the lines and fuel rail with compressed air. I don't have a code reader and wouldn't know how to find one.

 

[JLArangerdriver]

Man you have so many possible points of failure there...

Ok. One. Are you **sure** the injectors you bought are the same flow rate as the ones you took out.

No, I'm not. I couldn't read any part numbers on the old ones. I looked up the new ones and they said they were compatible, I would think the flow rate would have to be a lot lower than the factory ones to cause misfires, but I should probably go look them up again to check the flow rate, and see if i can find what the factory spec flow rate is.

 

[PetroleumJunkie412]

No, I'm not. I couldn't read any part numbers on the old ones. I looked up the new ones and they said they were compatible, I would think the flow rate would have to be a lot lower than the factory ones to cause misfires, but I should probably go look them up again to check the flow rate, and see if i can find what the factory spec flow rate is.

14 or 15 iirc. I can't remember off the top of my head.

 

[JLArangerdriver]

(Update) Compression test results weren't as good as I hoped. 1-170 PSI 2-165 PSI. 3-160 PSI. 4, 5 and 6 were all 150 PSI. If my math is right that's just under 12% difference from highest to lowest, I wouldn't think that would cause misfires, but all the low ones being on the left bank does make me worry a bit. The plugs didn't look that rich.

 

[PetroleumJunkie412]

(Update) Compression test results weren't as good as I hoped. 1-170 PSI 2-165 PSI. 3-160 PSI. 4, 5 and 6 were all 150 PSI. If my math is right that's just under 12% difference from highest to lowest, I wouldn't think that would cause misfires, but all the low ones being on the left bank does make me worry a bit. The plugs didn't look that rich.

Well. Now you know its either a 159,000 or 259,000 mile truck.

 

[PetroleumJunkie412]

ECM/computer is messed up. I'm not sure how I'd even go about replacing that last one, does it need to be programed to the truck? I could probably spend a lot of money replacing all of these and with my luck lately, it still might not fix it.

Ecm is not programmed to the vehicle. The computer itself is in the passenger kick plate, will have a three digit code on it known as a catch code. If you get me your code, I may have one laying around here I'd let got for a few bucks.

 

[JLArangerdriver]

Update: It's not fixed, but a lot less bad now. I discovered my cartridge type fuel filter housing, that was never meant to have a filter in 87, from what I read, was leaking pretty bad. I wanted to try and find a new o ring, and maybe put some gas resistant sealant on the thing, but it's jammed up between the frame rail and transfer case, and I couldn't get it unscrewed. So i had to remove it. In removing the fuel lines, one of the nipples broke off, the 80's plastic didn't hold up so well, I guess. I've bypassed it, and the truck runs much better now. It has more power, but it still feels a bit weak to me. I can still get some roughness/ misfires going up hills under 1,500 RPM or so, but again, way less noticeable than before. I've read that bypassing the filter housing can cause fuel starvation issues at high fuel demand. so I'm wondering if there's an easy option to maybe upgrade the in tank pump or the in line pump. I read up on how to get the codes of the computer, and the only code it shows is the EGR not opening, (which is deactivated). I've been thinking about these symptoms a lot, and I've decided the most likely issue is those cheap'ish injectors I installed. I didn't test them in any way. one doesn't even match. (long story). 5 of them are skp skfj712, and I read on here that some people had bad luck with those. The other is a standard motor products fj5. I think they are the same flow rate, but i wasn't able to find good info on that. The fact it has never backfired and isn't running noticeably rich would lead me to a fuel delivery issue. I really should of figured that out sooner.

 

[JLArangerdriver]

I' thinking it might not be a bad idea to change out the O2 sensor, as it might be the original ,it's defiantly old. and I understand they can start having issues before they completely fail, but I doubt that's the cause of my issues.

 

[ryan445]

I will add. I replaced two mismatched injectors with the Skp injectors and they made my problem worse. Just to reinforce what your hearing a little.

 

[PetroleumJunkie412]

I' thinking it might not be a bad idea to change out the O2 sensor, as it might be the original ,it's defiantly old. and I understand they can start having issues before they completely fail, but I doubt that's the cause of my issues.

Don't use aftermarket. Use Motorcraft.

Been through this a few times. Unless you're tuning off a wideband, always use OEM.