1990 5.8L burnt plug boots.
 

Hi guys,

Having some trouble with my 1990 burning plug boots on cylinder # 2, 3 and 4. The engine has a block off plate for the EGR and a "dummy " plug inserted into the EGR sensor to keep the ECU happy (everything else is stock) However along with the burning plug boot issue on 2, 3 and 4 I also notice the air tubes to cyld 3 and 4 are hotter that the rest of them after a short period of time running. I am wondering if this condition could be caused by blocking off the EGR and if so why the air tubes to only these two cylinders are way hotter than others .

The van runs great at highway speed but does have a stutter at idle, especially with the A/C running. At first I suspected a vacuum leak but can not find one. The van has a new distributor, cap , wires, plugs , ICM and base timing was set at 12* The van only has 36k original miles.

Any Ideas on what could be causing this issue or what to try to diagnose it ?

Many Thanks,

Sounds like you have the hated spider manifolds on that motor, I don't understand why that mess even exists. Does your vehicle have to pass smog tests? If not the best thing you could do is delete the whole system but that means changing exhaust manifolds in your case and that won't be any fun in a van. Your EGR disable won't be the root cause of your problem but it may be contributing, where is the EGR blocked off and is it sealed air tight? Is the EGR tube still connected or been removed? If present what condition is it in? There cannot be any exhaust leaks from any part of the EGR or the air injection system as this will affect fuel mixtures. Also vacuum lines in these systems must be intact and there can be no leaks, the EGR valve could be a source of a vacuum leak if it's diaphram is broken, better to disconnect and cap this line.

The EGR was removed completly and a block off plate was installed at the intake, The EGR tube was also removed and the exhaust manifold was capped off so there would be no exhaust leak. I can find no vacuum leak anywhere in the engin bay and the air pump system is still intact. The vehicle does not have to pass a smog test but I don't have the time to remove everything . The only reason I deleted the EGR was because the tube rusted out and I didn't want to put any money back into a system I did not really need on the vehicle.

Any Idea what could be causing the condition of burnt plug boots on these cylinders ?

Could be dirty or leaking injectors. Have you looked at the plugs lately? If some of the injectors are leaking fuel then fuel pressure will drop immediately after the engine is shut off and those plugs would be black or dark compared to the others. The computer will try to compensate by leaning out the overall mixture but that will lead to some cylinders running lean and that would cause an uneven idle and a miss

Just got around checking the plugs today. They all look uniform in color ( light gray )with no carbon buildup but that being said I have only had this unit for 3 months and have put very little miles on it. The P.O. said he had new plugs and wires put on it but I do not know the milage that this was done. At this point, what do you guys recommend I do or check ?

Many Thanks,

Cheap wires do tend to get burnt, also consider adding silicone heat sleeves which will prevent the manifold from burning them.

Light grey plug is too lean.. should be tan brown, can you check fuel pressure? It should be 32-35 at idle and it should raise to about 40psi with vacuum removed from the regulator.

Just ordered some heat sleeves, will have to reserch how to check the fuel pressure and post results when completed.

There is a shrader valve on the drivers side fuel rail.. looks just like a tire valve. Auto parts stores will often have a tool rental/borrow program where you can get a gauge set.. usually a fluid filled gauge, a hose that screws onto the sharder valve and a bunch of adapters. You can also do it red neck style with a common tire pressure valve but you may get gasoline squirting everywhere which is dangerous to say the least.

I could not find the Shrader valve on the fuel rail, would it be towards the front or back of the motor ? I did make a video of the situation along with a " leaking down " noise that I cant seem to find, not sure if it is related or not :


Many Thanks,