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Old 08-01-2022, 11:39 PM   #1
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Bad stumble in 1994 Ford E350 7.5L C Class

Hope some of you old-timer techs are still around ; ) I'm having a simular problem that I read about in an 8 year old post here.

I'm a retired used car dealer tech so I have a little experience.

It has more than a misfire more like a stumble and even died on me one time while idling. It seems to have gotten worse over time. It use to only idle rough when it was hot or up at high elevations.

It's a 1994 (Fed emissions) Ford E350, 7.5L with 73K miles. Note: Check Eng lamp works and has never come one.

In the beginning when we purchased it two years ago it ran ok but had a lot of exhaust leaks (RH side) Milling the exhaust manifold and installing a new metal to metal flared flange pipe fixed that. But did not effect the problem I'm still having.

I also decided to do some maintenance as I was not sure how old the wires or plugs were.

Installed new premium wires, including the coil wire. New dist rotor. Cap look good. Air filter is new. Note: Good even plug color on all plugs, no signs of oil usage or fouling. Engine uses 1/2 quart every oil change.

replaced O2 sensor while I was doing the exhaust.

Still same stumble issue.

I though I'd check the base computer timing as I have seen some guys set it without removing the gray timing spout a couple times at the dealership. Come to find out mine was set at 10ATDC! They even had the crank marked incorrectly with white paint... OMG! Still has the stumble but the difference in power is like night and day.

Before heading to the next Thousand Trails park I also checked the fuel filter and reverse blew all the gas into a jar... It was moderately discolored (not from dirt) age/bad gas fillup? But smelt ok compared to fresh gas. (No dirt) (I'll post some pics off my phone later)

So I added some Chevron Techron gas additive to the 1/3 tank and drove it a bit before heading up the hill to our next campsite... Yes, it was pinging pretty good at medium throttle and above now that the timing was set at 10BTDC. After driving it for 90 minutes with the gas generator running too I got it down to the red indicator on the fuel guage then headed to the Chevron station and added 22 gallons of fresh 91 octane fuel.

Headed up to our 7200 foot campsite in the mountains... After the new gas worked it's way through the lines the pinging stopped... Power was way up felt like I gained another 50 HP! It now pulls harder at 7K feet than it did at 1K! But still has the stumble :/

What I found so far:

Timing was off 20 degrees!.... When set at 10BTDC I did check how accurate it was on the marks... It might of varied 1 degree at the most so the timing chain should be ok. I used to get 6 to 8 mpg.... Hmm?

I also did a dry compression test when I had the plugs out. All cylinders were at 145 to 150 and all had a good strong first compression stroke. So I did not bother with a wet test.

Stumble is very noticeable at idle it's not consistent you can at times feel it at light throttle but never at medium or full throttle. Man I thought I had it with the bad gas find :/

I have aux coolant and trans temp guages: Running a bit cooler now 195/200 heading up the mountain (has a 185 T-stat) Ambient temp was 95 at base of hill, 75 at the peak.

When it stumbles you can hear it out the exhaust pipe too.

THINGS I STILL NEED TO CHECK AND DO:

Check idle vacuum (guages at my son's house)
Check fuel pressure (it does have a test port at the fuel rail)

Things to check further...
EGR
PCM (capacitor leakage?)
Fuel regulator on the fuel rail?
Scope check it with my Matco scanner as it has the scope module (at my son's house)

Things to rule out...
Fuel pump
Gas quality
Fuel filter
O2 sensor
Cat plugged
Engine condition and Ignition system


What do you guys think? Thanks!
Ken
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Old 08-02-2022, 06:24 AM   #2
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You should get a scanner (tunerpro RT) that reads "live data" from your OBD port. It will give you everything from coolant temps to injector pulse width.
It could be something as simple as a bad coolant temp sensor. The sensor for the gauge is not normally the same one as for the ECM.
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Old 08-02-2022, 09:17 AM   #3
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So.. what I would do.. is see if obd1 or obd2.. they changed along those yrs.. if obd1 you need a obd1 Ford scanner.. for about 30.00 last time I checked.. yes.. you can jump certain pins on diagnostics connection next yo battery.. but the Ford obd1 scanner will let you run extra tests.. if obd2 than connection is under dash inside.. for that you need obd2 scanner with live data.. good one to start with is around 200..
You most likely have bad capacitors in ecm going bad.. takes about 30mins to check.. you have to pull battery and behind that is ecm and it comes out under hood.. you will be able to see the bad capacitors.. you tube Ford ecm bad capacitors..
Next dirty IAC.. you can clean and reuse .. try it.. and dirty TBI. All this is on you tube.. if you plan to keep.. you need basic automotive repair book for Ford vans 1994 yrs.. I like Haynes and Chilton.. I have both.. it will give you specs and wiring diagrams and great troubleshooting steps.. check fuel pressure 1st. If you don't have tool.. most a/p store will rent for free.. but at this point you have to order books online.. while getting f/p gauge/tool at a/p store.. check for book..
The only way you can set timing is with spout connector off.. you must remove it.. and on my 1993 Ford conversation van I have 5.8l and you have to look closely at the timing marks.. you only use the hash marks if factory is using computer to check timing.. you have to wire brush the outer ring on harmonic balancer and there are very tiny numbers engraved on it.. I am not sure about 7.5 .. I just double checked Haynes pg. 1-42 and that is how they show it.. exactly like I described.. on vans with spout connector..
It will run great if you don't pull spout connector and adjust timing.. but it will ping under load and light throttle.. and you will destroy eng in short order..
That is my starting point.. I know my signature shows rv is workhorse.. but I have a 1993 Ford conversation van.. I bought new and have owned for 30+ yrs
Good luck and keep us posted
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Old 08-02-2022, 11:35 AM   #4
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Quote:
Originally Posted by donr103 View Post
So.. what I would do.. is see if obd1 or obd2..

It's OBD 1. I'll look into a scanner as my $3,000 Matco is only good for running a ignition scope check on it.

they changed along those yrs.. if obd1 you need a obd1 Ford scanner.. for about 30.00 last time I checked.. yes.. you can jump certain pins on diagnostics connection next yo battery.. but the Ford obd1 scanner will let you run extra tests.. if obd2 than connection is under dash inside.. for that you need obd2 scanner with live data.. good one to start with is around 200..
You most likely have bad capacitors in ecm going bad.. takes about 30mins to check.. you have to pull battery and behind that is ecm and it comes out under hood.. you will be able to see the bad capacitors.. you tube Ford ecm bad capacitors..

The PCM is high on the list as it's effecting more than one cylinder on each stumble.

Next dirty IAC.. you can clean and reuse .. try it.. and dirty TBI. All this is on you tube.. if you plan to keep..

I forgot to mention that I replaced the IAC a couple of months back... when the symptoms were much milder and only at high elevations. Hmm... mankes me think somekind of vacuum leak that has gotten more progressive? I still have the old IAC.


you need basic automotive repair book for Ford vans 1994 yrs.. I like Haynes and Chilton.. I have both.. it will give you specs and wiring diagrams and great troubleshooting steps.. check fuel pressure 1st. If you don't have tool.. most a/p store will rent for free.. but at this point you have to order books online.. while getting f/p gauge/tool at a/p store.. check for book..

I have all the guages, just need to swing by my son's house. I use to have a huge tool box but not anylonger... Most used tools are in the RV.

The only way you can set timing is with spout connector off.. you must remove it.. and on my 1993 Ford conversation van I have 5.8l and you have to look closely at the timing marks.. you only use the hash marks if factory is using computer to check timing.. you have to wire brush the outer ring on harmonic balancer and there are very tiny numbers engraved on it.. I am not sure about 7.5 .. I just double checked Haynes pg. 1-42 and that is how they show it.. exactly like I described.. on vans with spout connector..
It will run great if you don't pull spout connector and adjust timing.. but it will ping under load and light throttle.. and you will destroy eng in short order..

On the spout connector (over by the battery) it was removed before setting timing, engine turned of and then restarted with it still off. I physically marked the crank timing with a full length white mark so the timing is dead on 10BTDC. There is no pinging with premium gas but not sure on regular gas.

That is my starting point.. I know my signature shows rv is workhorse.. but I have a 1993 Ford conversation van.. I bought new and have owned for 30+ yrs
Good luck and keep us posted
Funny before all of this it passed it's California two speed smog test a year ago... Wonder if it still would with the timing now set properly... Time will tell!

Thanks!
I'll keep this post updated as I get more data.
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Old 08-02-2022, 01:41 PM   #5
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Mine i had was a 94, had a small skip, stumble at idle,, for years .. it was random.. I had my snap on scanner on it many time,, readings dead on or for a 140K plus unit..

You could see the idle change a tad..

That I did find was my TPS voltage at idle was way off.. They are mon adjustble other than twisting the throttle plate shaft..
I actually oval ed the holes a bit and got the idle voltage at .87-.92 ish.. still stumble but, shifting improved.. and it ran better..

one day, it stalled as it would on occasion.. It started up,, chugged, black smoke .. would move, that was it.... Well pin out box was borrowed after tossing some sensors at it..

You could unplug every sensor,, map tps, temp, o2 etc.. It would sit there and run, rev a bit, no power.. It would lose the 5v reference.. If i removed 2 sensors I would see the 5v reference come back.. strange.. the manifold temp sensor we found shorted ,, but that was partial issue.
Story ends with bad caps in ECM, changed it, ran great, stumble gone.. new owner has 210k and still running..
He did have an exhasut mis after I sold it, it was heat shelids on plugs, missing, fell off, plus wire would get hot and fail. mis fire..


OH back to the ECM caps,, they bad one were part of the volatge for 5v reference.. If way back, when it ran ok but stumbled,, a look at the 5v reference on a scope would have showed the mis/skip at the pattern was breaking down.. the computer rebuilder told me that....
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Old 08-02-2022, 02:32 PM   #6
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Quote:
Originally Posted by sibe View Post
Mine i had was a 94, had a small skip, stumble at idle,, for years .. it was random.. I had my snap on scanner on it many time,, readings dead on or for a 140K plus unit..

You could see the idle change a tad..

That I did find was my TPS voltage at idle was way off.. They are mon adjustble other than twisting the throttle plate shaft..
I actually oval ed the holes a bit and got the idle voltage at .87-.92 ish.. still stumble but, shifting improved.. and it ran better..

one day, it stalled as it would on occasion.. It started up,, chugged, black smoke .. would move, that was it.... Well pin out box was borrowed after tossing some sensors at it..

You could unplug every sensor,, map tps, temp, o2 etc.. It would sit there and run, rev a bit, no power.. It would lose the 5v reference.. If i removed 2 sensors I would see the 5v reference come back.. strange.. the manifold temp sensor we found shorted ,, but that was partial issue.
Story ends with bad caps in ECM, changed it, ran great, stumble gone.. new owner has 210k and still running..
He did have an exhasut mis after I sold it, it was heat shelids on plugs, missing, fell off, plus wire would get hot and fail. mis fire..


OH back to the ECM caps,, they bad one were part of the volatge for 5v reference.. If way back, when it ran ok but stumbled,, a look at the 5v reference on a scope would have showed the mis/skip at the pattern was breaking down.. the computer rebuilder told me that....

Interesting.... I found a rebuilder on ebay... They want $250 You send it in and they rebuild it and update flash if needed.

I'll check the module out this week and post some pics
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Old 08-02-2022, 02:46 PM   #7
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Pics

Here's how far the timing was off. White marks are where it was set to.

Load of bad gas? Per my previous post
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Old 08-03-2022, 05:11 AM   #8
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Quote:
Originally Posted by kctrading View Post
Interesting.... I found a rebuilder on ebay... They want $250 You send it in and they rebuild it and update flash if needed.

I'll check the module out this week and post some pics
If you find it bad,
Auto ECM Computer Exchange
124 Wynchurch CirPittstonPA18640 has one on the shelf.. he is online.. too
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Old 08-03-2022, 05:35 AM   #9
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A bad intake manifold gasket will give you grief.

Remove the PCV valve from the valve cover and then cover both the oil fill and PCV holes.

If you get any suction, that's a sign of bad gaskets.
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Old 08-03-2022, 11:02 AM   #10
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A bad intake manifold gasket will give you grief.

Remove the PCV valve from the valve cover and then cover both the oil fill and PCV holes.

If you get any suction, that's a sign of bad gaskets.

Good idea to check. But wouldn't the oil consumption go up as well? I don't use any oil
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Old 08-03-2022, 11:02 AM   #11
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Originally Posted by sibe View Post
If you find it bad,
Auto ECM Computer Exchange
124 Wynchurch CirPittstonPA18640 has one on the shelf.. he is online.. too
I'll check them out... Thanks!
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Old 08-03-2022, 11:13 AM   #12
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As mentioned above here are some pics

I did have two big bottles of Chevron Techron added to the gas... Wonder if that discolored it somewhat too?

Anyone got some laying around to check?

Jar on right is two month old gas that was in a sealed container.

The white marks was were the timing as set at 10ATDC with spout disconnected and engine turn off and restarted.

This is where 10BTDC is.... Make a huge difference in lost power... Most likely the last person who timing it did not disconnect the spout when setting it :/ Should of check this sooner than later.

Trip up to 7,000 feet was pretty awesome as it now has more power than it did down at 1,200 feet. No pinging either

Just got to figure out the stumble then I'll be set....going to get the rest of my tools today so I'll post some findings later this week.
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Old 08-03-2022, 10:14 PM   #13
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I had a 94 Nissan few yrs back, CHECK ENGINE, OBD-1, read codes thru flashing lights on the CPU Box for EGR, decided to start checking hoses/ vacuum lines and replace; finally found a 1/2x 2" long VACUUM LINE HIDDEN behind a device next to EGR that was fried and crispy, and replacing cured issues.
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Old 08-04-2022, 04:43 PM   #14
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Well... I blocked off the EGR with aluminized tape... Still stumbles.
Check for intake manifold leak on inside and outside... Pinched off pcv hose got the nice pulsation-back and forth on the paper I placed on the fresh air intake hose to the valve cover. No leaks found with car spray or using a 3/8" gas hose to the ear trick.
IAC sounds constant at idle via TBI hoses.
I also pulled the PCM and the circuit board looks normal with no capacitor leaks.... I'll post some pics.
Still has the same stumble when the fuel regulator is disconnect... has good vacuum signal to it.
Did not make any difference when I shorted out each spark plug wire.
Compression was consistent at 145/150 dry. Good strong first pump on all holes.
Has fresh premium gas... Timing set at 10BTDC with gray spout disconnected and tested on a restart... Timing reading remains constant at idle even with stumble.

Has new premium wires and Autolite copper plugs... Fuel filter is new and recheck it... Ok.

I can't find my fuel pressure test kit so I may have to buy one...
Will test the fuel pressures soon. May also have an injector issue?

Ah, I forgot to attach my vacuum gauge.... Will do that in a bit and report back.... Maybe video it.
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