88 2.9L Misfireing/backfireing issue

[Mark_88]

Mark

I found the problem it was the positive battery cable when I disconnected the air temp sensor. I fired it up it died tried it again it died the third time all power went off. I took and checked each wire the positive wire the crimp on the end where it bolts to the relay I moved and all came back on. I took it off crimped both ends tight

OK, glad you figured it out and can focus on the original problem...

That is what used to drive me nuts...I'd be working on one thing and somehow complicate the issue...resulting in much longer and more frustrating repairs...

 

[88 XLT Ranger]

There is not an idle adjustment screw on the throttle body, this is not like a carbureted engine. Do not adjust that screw to try and fix idle problems.

That screw is to calibrate the TPS and set the "throttle closed" point; the computer uses the IAC valve to regulate idle instead of using a screw to hold the throttle plate open a certain amount.

Spott thanks

No............. I would never do anything unless I know from folks like you its not going to effect anything factory set. This is why this TRS urgent help is so important getting great help from all of you that know and been through ordeals like this. I hope cleaning the idle air control valve will get this back to normal idle. The idle use to go to 1400rpm's cold start for a few min and come down to 800rpm's. I know disconnecting the air temp sensor helped but with the idle it wants to die if I don't give it some throttle to at least 1000rpm's

 

[88 XLT Ranger]

OK, glad you figured it out and can focus on the original problem...

That is what used to drive me nuts...I'd be working on one thing and somehow complicate the issue...resulting in much longer and more frustrating repairs...

Thank you Mark

Your great help is so very much appreciated I had no idea my first thought was the computer shutting power off. When I disconnected the O2 sensor I had no issues with power shutting off. The temp sensor and air temp sensor both gave me dim lights inside and than power shut off. To many issues at once will drive one nuts "Thank You" again. I bought this truck brand new from Harrold Ford its so clean some think its newer than 1988 at the gas stations. I hate to give up on it and this time buy a well used 4x4 from a used car lot. If I don't get this issue figured out I do very much appreciate all of you TRS folks taking the time to try to help out

 

[88 XLT Ranger]

Well something worked


I got the Idle Air Control Valve off and cleaned and put back on it idles great now. It seams a bit smoother running I looked inside the hole on the plenum I see its wet greasy looking. Is it passable to remove and clean the Air Temp Sensor? I see its going into the plenum intake runner. I was thinking maybe its got oil carbon buildup on it

 

[Pauls 4x4]

The idle valve was probably sticking, in "adaptive fuel off" it doesn't move from the middle position and the engine tries to stay at 800rpm hot or cold but it should stay running when warm (no warm-up cycle). But that stall cut out all the sensors from the equation, it's an "un-metered stall"

Since the limp mode is slightly rich, Idle air was probably leaning you !way! out (remember I said the OBD1 says rich when lean..) > if you can idle in limp now after cleaning it (supposed to "null" in limp which it wasn't, meaning it was off in other states too)

so how's the backfire going? It gone?

Either way, the air temp sensor has a huge margin of error, I don't touch them unless they blow up as all replacements are crud (My 91 has been through 4 brands all died).

 

[88 XLT Ranger]

The idle valve was probably sticking, in "adaptive fuel off" it doesn't move from the middle position and the engine tries to stay at 800rpm hot or cold but it should stay running when warm (no warm-up cycle). But that stall cut out all the sensors from the equation, it's an "un-metered stall"

Since the limp mode is slightly rich, Idle air was probably leaning you !way! out (remember I said the OBD1 says rich when lean..) > if you can idle in limp now after cleaning it (supposed to "null" in limp which it wasn't, meaning it was off in other states too)

so how's the backfire going? It gone?

Either way, the air temp sensor has a huge margin of error, I don't touch them unless they blow up as all replacements are crud (My 91 has been through 4 brands all died).

Paul thanks for info on how the Idle Air Control sensor works. Cleaning it helped get the idle back right on cold start up. The popping is still there no change in that issue. I did disconnect the Air Temp sensor still popping I plugged it back and disconnected the temp sensor still pooping/missing. One thing I notice its in the 50 degree range here cold. The truck ran great to town and back until I got off the freeway its all down hill coasting. Once I tuned to go up the road its started popping. Once I got home the coolant overflow tank was bubbling and high on coolant level. I though it was from popping so much motor running hot

I checked the plugs all look good a brownish tint no steam clean looking ones. The oil looks good no milky color no snot on the oil filer cap. It may have a cracked head making this popping/missing ordeal. I bought some Moroso "All Weather Seal" part # MOR 35520 from SummitRacing.com its a block head sealer you can use with Antifreeze. I should have it here in few day's will put it in and cross my fingers

My friend put it in his 3.8V6 it had a leaking head gasket sealed it right up. After 4 years still holding up regular auto stores don't sell this Moroso sealer

 

[Mark_88]

You can test for leaks in the heads or block by doing the glove test...or condom test. With the engine cold remove the coil wire and open the rad cap and put a latex glove or condom (or similar item) over the rad opening so that it can expand as needed. Crank the engine a few times and watch the glove/condom for activity. If the glove expands it means you do have a cracked head or block...

To be honest though, again, this is unlikely the cause because it would happen all the time...not just when the engine is warm or under load after warming up.


Test it just to be certain you can rule that out...if the glove does expand it may explain some things...but I really don't think it will turn out to be the problem...

From what I've read here this typically comes up after you drive downhill and the engine is warmed up...then when under load and warmed up it starts to popping...which is why I suspected the TFI all along...

And from what you have already said the wire harness to the TFI (distributor) was loose until you zip tied it in place...which I can't actually picture myself because I've never worked on a 2.9 or TFI for that matter...just what I've read on TRS.

Was the TFI module moving around by any chance? As in loose on the distributor?

 

[Spott]

Don't use the block sealer unless you have proof of a head/gasket leak. It does work, but there are undesirable side effects that you should avoid if you can.

While a head/gasket leak can cause a misfire, I can't see it causing a backfire/popping. Also, a leak would get worse over time, while your problem seems extremely consistent.

 

[88 XLT Ranger]

You can test for leaks in the heads or block by doing the glove test...or condom test. With the engine cold remove the coil wire and open the rad cap and put a latex glove or condom (or similar item) over the rad opening so that it can expand as needed. Crank the engine a few times and watch the glove/condom for activity. If the glove expands it means you do have a cracked head or block...

To be honest though, again, this is unlikely the cause because it would happen all the time...not just when the engine is warm or under load after warming up.


Test it just to be certain you can rule that out...if the glove does expand it may explain some things...but I really don't think it will turn out to be the problem...

From what I've read here this typically comes up after you drive downhill and the engine is warmed up...then when under load and warmed up it starts to popping...which is why I suspected the TFI all along...

And from what you have already said the wire harness to the TFI (distributor) was loose until you zip tied it in place...which I can't actually picture myself because I've never worked on a 2.9 or TFI for that matter...just what I've read on TRS.

Was the TFI module moving around by any chance? As in loose on the distributor?

Mark

The TFI module connector was loose due to my stupidity I didn't have it pushed in all the way. I took and pushed hard it snapped in the TFI module is tight on the dist. It pops / misses on first start up cold three times that goes away sometimes starting it let it warm up than re-start the popping goes away until the normal popping going up hill or down hill the little ground wire from the TFI harness to the back of the head is tight I don't see any wire issues

 

[88 XLT Ranger]

Don't use the block sealer unless you have proof of a head/gasket leak. It does work, but there are undesirable side effects that you should avoid if you can.

While a head/gasket leak can cause a misfire, I can't see it causing a backfire/popping. Also, a leak would get worse over time, while your problem seems extremely consistent.

Spott

I went and bought a new radiator cap the truck on cold start up I let it run 10min shut it off. After I shut it off a few seconds later it bubble up in the overflow tank. After driving and stopping for 10 it sucks the upper and lower radiator hoses together and fills the overflow tank. I have to pull up to get the inner rubber to let go its a tight vacumme. After that it suck the coolaint back in. I notice a few times the heater hoses like they had air or maybe air bubbles going through them a weird sucking whipping sound. Would a cracked head do this? you would think white smoke and it wouldn't run at all let alone 65mph before popping/missing

The temp gauge is never above halfway I don't think its overheating. why would the radiator cap suck so tight. It pushes the coolant into the overflow tank but don't suck it back in

 

[Mark_88]

I just read another thread that was an ongoing and frustrating ordeal for another member...he just posted that they finally found the problem...it was a scorched wire harness...

Have a read through...similar symptoms...but more like hesitation...and a 4 cylinder not the 2.9...

http://www.therangerstation.com/forums/showthread.php?t=168461

 

[Jtallen]

I am surprised no one has thought of this. Have you check for an intake mani leak? How many miles on this thing? Is it leaking any unusual amounts of oil? Burning? Have your tried unplugging your IAC valve and turning the idle up to where it will idle without it and seeing if it still misfires?

 

[88 XLT Ranger]

I just read another thread that was an ongoing and frustrating ordeal for another member...he just posted that they finally found the problem...it was a scorched wire harness...

Have a read through...similar symptoms...but more like hesitation...and a 4 cylinder not the 2.9...

http://www.therangerstation.com/forums/showthread.php?t=168461

Thanks Mark

I appreciate the link and will read through it this issue I have has to be electrical. Today it started popping from start up all the way home and each time I put in drive its drops to 500rpm's almost stalling. I put in park it goes to 1500rpm's than drops to 800rpm's it was also surging a bit at times. No bubbling in the overflow tank this time. There is one big wire harness going from drivers side over across to the engine. This harness had dropped down to almost the exhaust manifold at one time I see the outer protective flexable plastic around it melted at the bottom. I see no wires melted will take it apart look over each wire in the morning with my bright shop light

 

[88 XLT Ranger]

I am surprised no one has thought of this. Have you check for an intake mani leak? How many miles on this thing? Is it leaking any unusual amounts of oil? Burning? Have your tried unplugging your IAC valve and turning the idle up to where it will idle without it and seeing if it still misfires?

Thanks for the help

How would you check for an intake leak? this issue sometimes it runs great than popping /missing others. I haven't disconnected the IAC and I don't want to mess with the factory set idle looking screw. It don't leak oil or burn oil when on a level road at 15-25-35 mph It pops than a few seconds pops and has no power unless you floor it the truck will rev up in low gear. When it not popping missing it runs perfect 65mph up hill but not for long it goes to bogging popping missing again

 

[88 XLT Ranger]

Update on my on going Saga s

I took and removed the air cleaner box and intake tube. I had a clear view and was able to look the wire harness over real good. Its the one coming from the computer to the fuel and computer relays over across to the engine. I could not find any issues with wires all looked good. I disconnected two wire connectors on that harness for corrosion all looked good. I put all back together fired it up it would only go to 800rpm's lopping slow almost stalling. I went around I herd one pop than it started running perfect again. Once it warmed up I shut it off started it again it went to 1000rpm's and came down to 800rpm's in two seconds. The Idle Air Control valve seams to be wacky again