Help, my engine is suffering.

[Lobo]

My '92 has been having some engine/performance issues over the last month. Ever since the weather has warmed up my Explorer has been running roughly and performing poorly. I put in a new Fuel Pressure Regulator earlier this week and it seems to have smoothed out the throttle response and lightened up the exhaust fumes. I was hoping that the FPR would solve some of the other problems but so far it hasn't. Yesterday it was 90+ degrees out and the engine ran really rough especially when I turned on the AC. With the AC on acceleration was practically non-existent and it actually died once. I never had that much of a performance degradation with AC on in the past. I would like to try to get it taken care of the is weekend (as long as it isn't too major). I was thinking of starting by decarbonizing (with a carbon flush). If anyone can reccomend a carbon flush product I would appreciate it. Then possibly replacing the spark plugs (they are only a year old). From there I am looking for suggestions. Please let me know if you have taken care of the problem or have some insight. I have looked through the other threads but wanted to add my specific problems. Thanks for you help!

 

[SteveVB]

Lobo,

You should check the Throttle body and the MAS and clean them. I clean my TB every year and it is worth the trouble. Take it apart and clean it and the IAS with a cleaner.

This will clean up an idle or closed throttle stumble- you didnt say when the rough running was occuring, but if like mine when you had the A/C running it wouldnt hold an idle, or the idle was choppy and when coasting it would surge, then the cleaning will help. The procedures are in most manuals and on the can of gumout throttle body cleaner I have. The procedures for cleaning the MAS are on this site under FAQ I think.

Good luck.

 

[Lobo]

The engine is ideling roughly and accelerating somewhat roughly from a stand still. It is also running roughly when on the highway going about 50MPH at ~ 1700 RPM.

What type of cleaner should I use on the IAS?

 

[SteveVB]

I use Gumout- Air intake & Throttle body cleaner. I take off the intake hose and spray down the TB and scrub it with a tooth brush, also the butterfly. Then remove the IAC and clean it out. You can also follow the directions on the can or in the service manual. For the MAF check the article on this site, the MAF uses a different method and chemicals to clean it.

Have fun.

 

[ERIC]

And make sure you have reset your computer after doing all the cleaning. You probably will have pulled the battery cables while cleaning the MAS, but if not, do remember to pull them to reset the computer.

BTW, Steve, you said you used a toothbrush on the inside of the TB while cleaning it. I thought the TB throat had a special coating on it, and you had to be very careful not to mar or rough it? How many times have you done this...I assume it has never caused you a problem?

 

[SteveVB]

Eric, probably cleaned it 10 or more times. I use a tooth brush which has nylon bristles so it doesnt damage anything on the TB. Tooth brush helps the chemicals work a little faster.

I wouldnt use any thing with stiff bristles small wire brushes etc, but the tooth brush wont hurt anything.

 

[ERIC]

No, Steve, I understood you were using a toothbrush, not a wire or something like that. I just had in the past been REAL concerned about this coating. Thanks for your reply...obviously I can relax a little bit about it. That's good to know.

 

[TPLYNCH]

Lobo, your Idle Air Contol unit might be bad as well. This is the part that controls the engine idle and is supposed to increase revs to compensate for the drag on the engine when the a/c is turned on. If it is not working properly, your engine will either run at very low rpm or die on you at idle.

 

[Skip Pendle]

Since you report that the roughness is present from idle through acceleration to cruise at 50MPH, it sounds like there is a cylinder that is not doing its job.

The easiest way to verify this is to remove one plug wire at a time from the ignition module...the one that doesn't make any difference in the idle is the culprit. From there you have to check if it is the plug, the wire, the ignition module or the injector that is causing the problem.

One hint: if you find 2 wires that don't make a difference in the idle performance, then it may be the ignition module. On the 4.0L engine, the spark goes to pairs of plugs at the same time (there are only 3 ignition coils in the module).

Good Luck.

 

[JoeC5]

Carbon Flush? Is that the name for the product to decarbonize your motor? I read a thread about that but i cant find it anymore. It said something about spraying it into the brake booster vacum hose? Can someone explain this process to me. Thanks guys.

 

[FMNavajo]

Lobo,
Check the air control unit like TPLynch sugested but if you are going to perform a carbon flush try this first, pull the #5 plug, (middle plug on drivers side), and any other plug and compare the two. If #5 has more carbon build up than the other try re-torqueing the lower intake manifold. Just a sugesttion but with the heat increase in the area you live it could have just caused your intake manifold gasket to finally give way. Also check your oil filler cap and see if you have any brownish substance built up that might be antifreeze getting in your oil which would confirm a lower intake manifold gasket failure.

just a suggestion,
FM

 

[Lobo]

Where is the idle air control unit and how would I test it? I looked in my Haynes manual but was not able to find the idle air control unit. The engine seems to be running pretty well now after cleaning the MAF sensor, throttle body and decarbonizing the engine (I had recently replaced the fuel pressure regulator and #5 plug). I may still have the problem when I use the AC but haven't had a chance to test it yet.

The #5 plug usually has more carbon deposits on it than the others so I clean and replace it more often. I am planning on changing out the intake manifold gasket in the near future.

I used Seafoam to decarbonize the engine. I sucked it into the engine through the brake booster vaccuum line. Then I let it sit overnight. Not sure how well it worked but it sure blew some incredible clouds of smoke when I ran it the next morning.

Thanks for all the help!