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eric remington
eric remington,
Category: Cadillac
Satisfied Customers: 275
Experience:  mechanic/service advisor at topline auto
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I have a 1990 Cadillac Deville with the 4.5L V8 with 85K

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Hello, I have a 1990 Cadillac Deville with the 4.5L V8 with 85K miles. It's have a rough idle as well as a shake felt through the steering wheel and gas pedal when under light load. If I stomp / chop on the gas, it smoothes out. When coasting, there's no shake. A mechanic told me that cyl#3 is misfiring. He went through the spark plugs, wires, and dist cap and had confidence that it wasn't an electrical issue. If I pull the plug wire off of cyl#3 at idle, it runs rougher, so she's firing, but maybe not always.Can the injectors have these issues of intermittent missing under different load ranges?
JA: How often does the vibration occur, and when did you last have the tires balanced?
Customer: Under light load only. It goes away if I power through it. I'm pretty sure that it's not unbalanced tires. It's dead-smooth while coasting. It will shake at any speed. It's only dependent on the engine rpm's and load.
JA: Are you fixing your DeVille yourself? What have you tried so far?
Customer: Mostly myself. I took it in to have the mechanic to look everything over (just bought it) and he told me to run Chevron Techron injector cleaner through it, only to make the issue a little worse. I've also replaced the in line fuel filter with no change and he had changed the plugs.
JA: Anything else you want the mechanic to know before I connect you?
Customer: If I'm cruising at 70mph, it gives me a rhythmic shake about every couple of second it shakes for about half a second, smoothes out, and shakes again, mile after mile.
Customer: replied 4 months ago.
I've been eyeing up some rebuilt 4-hole injectors on ebay for only $104 for all 8. I was just going to replace them all, hoping that will clear things up. I'm also contemplating buying a new fuel pressure regulator while I'm changing out the injectors since it will be easy to change at that time. Would either the injectors or FPR cause these issues?
Customer: replied 4 months ago.
Or could it possibly be something like the TPS or MAP sensors? Something possibly sticking when I accelerate slowly, but when I chop the throttle, something moves inside of the sensors and it can pickup on the input accurately?

H​ell there are several thing s that can cause a misfire......do you have acess to a vacuum gauge or scanner

Customer: replied 4 months ago.
I picked up a fuel rail pressure gage that I have yet to try. I don't have a scanner or a vacuum gage. It's not throwing any idiot lights. What were your thoughts if I were to rent one or both of those tools?

v​acuum gauge can tell you if you have mechanical problem or vacuum leak scanner can give other info....but ck engine vaccum it should be steady 18 inches. if its not steady what is it doing and where is it at?

a​lso you can listen to the injector to see if it is engaging disengaging by a clicking sound....but that doesn't tell you if its clogged or unclogged...if your vacuum gauge reads low vacuum like 14 15 and it is oscillating extensively.....compression test...if vacuum gauge is rolling like 13 or 14 then up to 16 17 it is a vacuum leak and you must find it....scanner can give you codes....ohhhh I forgot you can access codes from the heating and Ac unit...ill show you how to do that but do these tests first

Customer: replied 4 months ago.
Do I check the vacuum off of the throttle body, the same port as where the FPR connects? Also,are we just talking about 18 while idling, steady throttle, or chopping? I'll need to remove a few things in order to get to the plugs to check the compression (kind of buried). I'll have to get back to you next week with the results.

w​ell if you have a smooth 18 inches no compression test necessary....you need a vacuum source where vacuum present at idle.....only if you get rapid oscillations.. turn key on and push off and warmer buttons on hvac unit key on engine off see if any codes pop up

Customer: replied 4 months ago.
Well I got around to testing the vacuum through the hose coming off of the TB for the FPR and she measured a fairly constant 17+/-1 in Hg. The needle would bounce rapidly but by only around +/-0.3 and 0.5 at its extremes. The vacuum pressure would go up to about 20 if I held the throttle steady, above idle (no idea RPM, manually operating throttle from engine bay).Then I tested the fuel pressure and it was at 41psi while engine off, key on. Over about 10-15mins of testing the static drop with engine off, it dropped from 41psi to 30psi. This seems a bit fast correct? Thinking fuel pump? I've just replaced the in line fuel filter with no change in performance and I would think that the car would run worse the harder I accelerate, not smooth out as it's doing.When idling, the fuel pressure stays steady around 36-38psi.

ok good swap injectors and or coils when you scan it and find out which cylinder is misfiring compression test?

Customer: replied 4 months ago.
I had it scanned at Orieley's through the OBD1 port today and nothing came up. That's what u mean by "scan" right? The only code that came up when I did the key on and pushed and held the off an warm buttons on the HVAC was a code F11 which looks like a problem with the upper A/C temp circuit. Nothing on my misfire issue, but any recommendations on the F11 code?

any problems with ac? what about misfire yu have misfire on no 3? correct? so have you done any diagnostic testing to locate that issue

Customer: replied 4 months ago.
Yup, A/C just blows hot air. I got a bottle of refrigerate recharge, thinking that it was just low, but turns out that the compressor never kicks on. If the F11 code says that there's a problem with the high-end circuit, does that mean that is a problem with one of the sensors on the A/C condenser canister? I saw a sensor or switch coming off the canister and another one mid-line.It's still doing its rough idle / rythmic shake misfiring. It's been spurattic though. It ran great for 5 mins on a drive last night, but then started acting up again.

o​k I would swap injectors and or coils for misfire...I'm really only supposed to address one issue but fr you I will look up that code and advise you

Customer: replied 4 months ago.
Understood. The A/C is much more of a back-burner issue. I will swap the injectors and let you know.Will I need any gaskets or new seals to swap the injectors? The new injectors already come with new orings, but I'm curious about gaskets for other components that I must move out of the way to get the rail free like the power steering pump or anything else?

If you take any power steering componenets loose change orings

Customer: replied 4 months ago.
I was able to get the power steering assembly off to the side without disconnecting anything. Luckily the lines are JUST long enough to move the whole thing out of the way.Boy did I ever find out how many vacuum lines there are! Of coarse I snapped an elbow and there are some hoses that are very dry and in need of replacing.So now I've got everything out of the way, the fuel rail is loose, and I disconnected the gas lines and electrical harness. What's the best way to get the whole assembly out with all of the injectors pitched at different angles from eachother? Gingerly pull up on each injector at a time until the orings are out of each port and lift the entire assembly out?
Customer: replied 4 months ago.
Do you recommend any spray lube to help them pop out? They seemed a little stuck in there, but I didn't pull too hard. I didn't want to damage the rail at all and it's not the easiest to get a hold of the injector bodies with your hands...

I​f the only thing holding injector is an old oring you may have to put a little persuasion but I would soak it with some penetrating oil for a couple of hours

so how is it going?

Customer: replied 4 months ago.
Sprayed some penetrating oil and used a wide and dull chisel wrapped with a rag to pry up on the fuel rail by each injector.Ohm tested all of the injectors and found both cyl# ***** & 5 to be WAY out of spec!
#1 = 15.5
#2 = 12.8
#3 = 3.0
#4 = 14.5
#5 = 3.6
#6 = 15.4
#7 = 11.3
#8 = 10.8
All of the new injectors measure between 14.3 - 14.6. Very consistent....unlike the old ones. These new injectors don't quite seat as for into the fuel rail though, roughly 3mm less. Hopefully we don't have any leaks! I'm going to be installing it now.I've also gone and replaced the fuel pressure regulator while I have the rail off. Also replaced all of the old rubber vacuum lines. They were all cracked up once I touched them. Look fine from the outside, but the inside is cracked 3/4 through!

ok so replacing injectors is first step hopefully no damage to pcm as a result

yes good job a vacuum leak can cause huge problems sounds like you are on track...so let me know if it runs good at that point or whether we need to do more...sometimes its a step by step process, till all problems are resolved

Customer: replied 4 months ago.
Success!!! She's running nice and smooth, has much more get-up. No more shake under load. I'll keep an eye on the injectors for a leak, but it looks promising in the first few miles. Thanks for the help!

no problem that is why I am here and at least part of the reward is knowing that your issue s are resolved thanks for using just answer. please do rate me as my compensation depends on that

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