I was suggested to this forum for some help with a recent problem I've ran into...

I have an 89 f150 with a 4.9. It has no cats, no smog pump hooked up, running brass cap and rotor, with msd coil, newer icm, and 8mm plug wires. The plugs are gapped to .047 and the timing is set to 12.5 degrees btdc.

The truck had a blockoff plate on the egr and no egr solenoid or vacuum routing when I got it. I removed the blockoff plate, and installed an egr solenoid and all necessary vacuum lines from a junkyard truck. This took away the egr codes, but the truck stumbles, almost like a missfire at around 2k rpm's at steady light throttle.

If I accelerate harder or floor it, the truck picks up and takes off running just fine. But if I stay at a steady 2k rpm in any gear(manual trans) it stutters. I tried cleaning the IAC to no avail. In the meantime, as it's my daily driver, I plugged the vacuum line again, but it still rode rough. So for now the blockoff plate is reinstalled.

The egr looks newer but I need to do a vacuum test on it still. The truck has no other related engine codes. The only codes are for the smog pump solenoids (which aren't there) and the ac clutch, but the ac doesnt work anyways. I want to have the egr working to gain an mpg or 2 hopefully, but I don't know what's wrong with it.

Any pointers, suggestions, or people with the same problem? Any help is appreciated. Thanks in advance!

 

i would try cleaning the egr really good that may help..

 

Subsribed to thread.

 

Bumped up so it didn't get lost.

 

try replacing the ignition. cap rotors plugs wires. you said it seemed like a miss, so treat it like a miss. ive just recently learned about the "sixlitre" tuneup. sounds like po tried it on your truck. bring it back to stock and see how she does... oh and a thought..... base timing for your truck should be 10* btdc when you made the egr work again it could be causing your problem. i know you said no other codes but check your connections at the spout and coil just for sh**ts and giggles

 

I did the "sixlitre tuneup" or the timing bump. It ran fine after. Stock is 10, im at 12 btdc. The cap, rotor, wires, and plugs are all in good shape still. I just rechecked timing and it is still the same, and spout is connected properly.

I'm leaning towards the IAC being the culprit, as it is still doing this with the egr blockoff plate installed. Which means it isnt the EGR system after all, my guess is the egr system was full of crud, and reconnecting everything dirtied up the IAC valve, which I just cleaned the day before reworking the egr system anyways. But I think the IAC is just worn out. I've cleaned it more than once and the idle at startup can sometimes bobble for a few seconds, so I think it just doesn't work like it used to.

Today I'm seafoaming the engine through the vacuum system, and afterwards replacing the egr valve gasket, IAC and IAC gasket. Then I'm doing the vacuum test on the EGR. I'll post back with results tonight. Thanks for the tips so far.

 

I did the "Six Ltr. Tune-up" 3 years ago on my 87' 302 w/ 87 octane, but w/ a 60K volt coil. I'm running .054 (+.010) & 16BTDC, w/no problem. I don't recommend "that much" base timing bump for most folks. The engine has to be healthy & everything functioning optimally & maintained at that level.

12BTDC is a mild reach & usually easily obtainable w/ some prep, if desired. Compression does not have to be great, just relatively balances.

That being said, I would agree that restoring to stock base time, till this problem is resolved is a good idea. Further advance of base time requires "all of your duck in a row". You clearly have at least one A.W.O.L. duck!

Is the same problem still apparent w/ the EGR blocked, but less noticeable, or alleviated completely?

Also wondering if this problem you're experiencing is why the PO removed the EGR system & smog pump function to begin with. Personally I'm not a fan of removal or disabling of either.

 

Did the problem occur after the ignition upgrade, fine before?

You mentioned you also installed a "newer" ICM (TFI). Newer?

 

Well it's running right now. But in case someone else needs to use this thread to troubleshoot, I'll go over all the questions.

The p.o. removed the smog pump and EGR for 2 reasons. 1) because he was a diesel mechanic and was convinced emissions controls were a myth. He thought the truck would run better without it. And in the case of the smog pump at least, I agree, its a stupid idea. and 2) the 4.9 in it now isn't original, he bought it with a bad motor and swapped in one with less mileage and just didn't want to hook all the smog stuff back up.

Blocking off the EGR again made little to no effect.

The TFI was brand new, but was replaced almost 2 years ago now.

The problem was recent, the timing upgrade was done 2 years ago also. However, the platinum plugs were put in about 2 months ago when I bought the truck back.

Here's everything I did yesterday, and how I fixed it....
I first changed the thermostat back from a 180 to a 195 degree, and flushed the coolant. I then dumped a bottle of fuel injector cleaner in the gas tank, and seafoamed the engine through the brake booster hose. After blowing 20 minutes of crud out a half an hour later, I then changed all the plugs back to coppers (the only way to fly) and gapped them to .055. Which, yes, is more than recommended, but fine with the advanced timing. Then I changed the IAC valve and gasket, and cleaned the throttle body. Finally I reset the computer and now its running excellent.

The problem was one of the front 3 cylinders had a missfire which showed itself more around 2k rpm than at idle. I could feel the miss in the exhaust pipe. I think it was mostly due to the platinum plugs, but the IAC made a huge difference as well. The truck idles about 400 rpms lower than before, at around 550 rpm and doesn't hunt around for idle at start up anymore. I still have the egr blocked off though. But now that everything is running well, I think I should be able to open it up no problem.

With a clean IAC, intake, and everything working well, I'm now pretty hesitant to bring dirty exhaust gas back in with the egr. If it's running well like this should I leave it blocked off, or will I get a significant enough increase in gas mileage to make it worth hooking it back up?

Thanks again everybody for the suggestions!

 

Although this thread had an lower than normal response to it, at least you have another source for reference in the future. Thank's for taking the time to share the resolution & glad to know you finally got a handle on it!

I've mentioned going w/ a 180F thermostat w/ the timing bump, but I'm running a base time of 16BTDC. I'm now thinking that deserting the stock 195F should be the "last" change considered & more based on each individual situation. While I have no problem reaching normal op temp at 16BTDC, at less dramatic base time set's, you may actually be sacrificing a longer time spent out of closed loop function (ECU assisted fuel trim) for the sake of erring on the side of "thermal safety" that in fact may be overly cautious, & fuel foolish.

The ignition system upgrade w/ the plug gap stretch/ base time bump isn't for everybody. It takes a little time & patience to do it safely & dial in the correct combination/balance, but I still think it's well worth the effort.

The wider gap you're able to run was actually courtesy of the higher output coil you upgraded to, not the further base time advance. I wish you would have mentioned the Double Plats. I would have told you to chuck em!