Community Forums

schulzee · 06-19-2016, 08:40 AM

I have a 1990 454 runs rough, pull #2 plug wire off and runs smooth or pull #4 and it runs smooth. It over heated had a 165 thermostat put in still over heated. Put new water pump and clutch fan took care of the over heating. Temp was on the cold mark test drove it and the temp when to the middle. Guy has had it for 30 days 240 miles away, still not fixed. May be some one on here can help.

GraySeal65 · 06-19-2016, 08:48 AM

Quote:

Originally Posted by schulzee

I have a 1990 454 runs rough, pull #2 plug wire off and runs smooth or pull #4 and it runs smooth. It over heated had a 165 thermostat put in still over heated. Put new water pump and clutch fan took care of the over heating. Temp was on the cold mark test drove it and the temp when to the middle. Guy has had it for 30 days 240 miles away, still not fixed. May be some one on here can help.

New cap. rotor, plugs and wires ? Check the firing order maybe 2 and 4 are switched ?

OLYLEN · 06-19-2016, 08:53 AM

Sounds like a compression check is needed. Pulling a wire and it gets smooth, it should have a constant miss. If compression passes the a scope of some type to see the electrical system.

LEN

TR4 · 06-19-2016, 10:27 AM

Head gasket between 2 and 4?

Dan Osborne · 06-19-2016, 10:46 AM

Quote:

Originally Posted by TR4

Head gasket between 2 and 4?

I was thinking the same thing. Especially since there was a recent overheating issue.

jelag · 06-19-2016, 10:57 AM

Does your vehicle have an EGR valve & catalytic converter on it???

Please follow along... vehicles with EGR Valves can have issues with the valve and it leaking... or possibly a problem with the manifold...

If when you pull a plug wire... and the engine seems to run smoother.... here is what is going on... that raw fuel... is leaving the exhaust valve, crossing over the passage in the intake manifold... and flowing through the EGR valve that's bad... and that raw fuel is enriching other cylinders and making the engine run smoother as the mixture is richer....

The EGR valve system is designed to work ONLY when your running down the highway and its a method to displace some of the air/fuel mixture in the combustion chamber with inert gas.... this lowers temperatures and emissions.... if the valve/mounting gasket/etc is bad... and is off its seat during low speed or idle operation it can make the engine miss...

Remember that at idle and low speed the throttle plate is closed... thus an engine that would normally have 150 psi compression, now with the throttle plate closed will have maybe 75 psi.... and the air/fuel ratio must be exact for good combustion... with the EGR off its seat... this can't happen...

Hope this helps...

BTW - most people have long since pulled the vacuum line off this valve so it can't function... that doesn't mean the valve is bad... one of the simple tests is to put some propane or other chemical on the shaft of the valve... if the chemical runs down the shaft and the engine smooths out... the valve is bad... OR pull the valve off the engine and pour raw chemical (carb cleaner/brake clean) and see if the chemical migrates past the seat...

schulzee · 06-19-2016, 05:09 PM

Yes it does.

schulzee · 06-19-2016, 05:19 PM

92TNTRacing He put a new distributor and cap on, talked him Thrus. told him to put new plugs in it. He say the EGR was suite.

jelag · 06-19-2016, 05:23 PM

If the EGR is at fault... the only way to know that is to do the tests as I've suggested above... For years I taught mechanics quick tests to verify failures of components... if he hasn't pulled it off and tested it... than he's just "looked at it".... oh it sitting there... and the diaphragm works... so it must be good...

These of course are just my thoughts... and I have been wrong some of the time...

schulzee · 06-19-2016, 05:40 PM

I will call him tomorrow, and see what he says. I have get this fixed. Will let you know what he says. Thanks for the help, so hard to do any thing so far away.

jelag · 06-19-2016, 05:54 PM

we used to power balance the engine with killing each cylinder, one at a time... if you had a bag EGR valve and you killed that cylinder close to the valve... the engine would speed up and run smoother... the only time in 20 years of doing this that it wasn't an EGR valve was on a new car the owner drove (GM DEALER) and I called it a EGR Valve or intake manifold... the tech found a cracked intake manifold from a bad casting...

Have your tech do the additional test... start the engine and put a vacuum meter on the manifold... slowly raise the engine speed from idle to about 2200 rpm... he should consistent increase in vacuum, what he sees is not important... he might start at say 18" and it goes to 22" or maybe from 20" to 25", you get the picture... if as he raises the RPM and the vacuum stays the same or slightly increases have him look for a plugged up catalytic converter.. as the volume of air increases through the engine.... (throttle plate is open and the engine is reving higher) the efficiency increases and the vacuum should go higher.. if it doesn't, there is a good chance the catalytic converter is plugged... there are a lot of early RV's where the chassis builder didn't PLAN for the added volume of air with a MH chassis or trailer tow package... and the converter fails and plugs the exhaust.... THAN the temperatures are higher at the EGR valve and some of these engines have issues with heating.. as the engine can't exhaust the heat....

Geez I hope all this helps and make some sense to you... there are a lot of tech's who have gotten way past the basics with all the computer related test systems today...

Tha_Rooster · 06-19-2016, 06:08 PM

I had a 1994 454 mech. cleaned radiators, changed fan clutch ended up being a cracked exhaust manifold melting the temp sending unit.

Kiawah · 06-19-2016, 06:52 PM

Agree with the potential blown head gasket, between the #2 and #4 cylinders. Do a cylinder pressure test.

lonfu · 06-19-2016, 07:20 PM

Quote:

Originally Posted by jelag

Does your vehicle have an EGR valve & catalytic converter on it???

Please follow along... vehicles with EGR Valves can have issues with the valve and it leaking... or possibly a problem with the manifold...

If when you pull a plug wire... and the engine seems to run smoother.... here is what is going on... that raw fuel... is leaving the exhaust valve, crossing over the passage in the intake manifold... and flowing through the EGR valve that's bad... and that raw fuel is enriching other cylinders and making the engine run smoother as the mixture is richer....

The EGR valve system is designed to work ONLY when your running down the highway and its a method to displace some of the air/fuel mixture in the combustion chamber with inert gas.... this lowers temperatures and emissions.... if the valve/mounting gasket/etc is bad... and is off its seat during low speed or idle operation it can make the engine miss...

Remember that at idle and low speed the throttle plate is closed... thus an engine that would normally have 150 psi compression, now with the throttle plate closed will have maybe 75 psi.... and the air/fuel ratio must be exact for good combustion... with the EGR off its seat... this can't happen...

Hope this helps...

BTW - most people have long since pulled the vacuum line off this valve so it can't function... that doesn't mean the valve is bad... one of the simple tests is to put some propane or other chemical on the shaft of the valve... if the chemical runs down the shaft and the engine smooths out... the valve is bad... OR pull the valve off the engine and pour raw chemical (carb cleaner/brake clean) and see if the chemical migrates past the seat...

I like to start at the beginning. For me it saves time. 1. compression test 2. leak down test between #2 and #4. 3. Check plug wire order 4. If new plugs/cap/wires (no cross fire) then EGR valve(replace). 5. Propane gas intake manifold test 6. check distributor timing to cylinder #1(timing chain?) 7. Coil 8. exhaust manifold test(shop vac exhaust to tail pipe with check with soap bubbles) 9. More electrical tests if all of above are ok