Always pull both intake manifolds and the injectors as a single unit. 24 nuts plus a few hose attachments and the like. Cake.
1 Like
Maybe your 4A injector is leaking when shut.
Iāve always thought I should replace intake manifold gaskets, since theyāre so old and itās impossible to know if itās perfectly sealed, so Iām just going to do it. Like you said, cake.
I also have read your comments in the past on filling those air pump holes with nail anchors. I like that idea better than the way I did it. Will be easy too with the manifolds off.
Looks like I have another summer project! 
If an individual injector was leaking when closed, it would most likely be delivering a higher than spec flow.( ieā¦the pintle does not seal 100% on the seat, and leaks when closed AND is held slightly open when operating from whatever trash may be present) In either scenario, the ECU would respond to the O2 sensor voltage (which should be telling the ECU there is not enough O2 in the exhaust for the volume of fuel being deliveredā¦and the ECU should reduce fuel delivery to all injectors on that bank.
SD Faircloth
A vacuum leak or too much air is sounding more and more like your issue. You say the ECU is suddenly commanding fuel to go very rich, and you have dialed it back.
SD Faircloth
1 Like
Yes, the ecu fuel trim has been quite steady the last year, ive been clicking it just one click rich or lean trying to fine tune my car.
Suddenly last week, i had to click four times leaner to get 1.9V, and then yesterday 3 more clicks leaner to get 1.9V. i thought it was my new downpipes, but that may have been a red herring.
Ive since turned it back 3 clicks richer, because i dont want the other cylinders to run too lean. Turning it rich to where it used to be raises idle a bit too.
Iād start on A bank checking every vacuum hoseā¦front and rear of intake manifold, under the throttle body I think lies one, and checking the vacuum line sticker, and anywhere else you or someone else can think of. SD Faircloth
I have, and all look good. There is definitely a hiss coming around middle of A bank intake manifold in the VEE, but I just canāt locate it, and squirting soapy water does nothing, and like I said, Iām too nervous to spray carb cleaner or propane in that area due to fire.
I am pulling the trigger and replacing intake manifold gasketsā¦iāve been putting it off long enough!
I have never tried soapy water to detect an intake tract leak . It seems to me that it would suck the mixture in and not produce any tell tale bubbles as in a leak on a tire?/ Results, inconclusive/
OTH. a vacum guage might be quite indicativeā¦ ā¦
Carl
I believe the old school method was to use plain water gently poured onto an area that was thought to be sucking air into the engine. if there was a leak, the water gets sucked into a cylinder(s) resulting in a variation in running of the engine. In Gregās case, if the #4A injector to intake seal was leaking, the water would get sucked past the sealā¦with a change in engine sound and running. I think cold water again poured into a carb was used to blow out carbon baked on a cylinder head. SD Faircloth
That will tell you an absolute value, but you need to know what the actual value should be for comparison. On a V engine, comparison with the other bank will probably do it. In this case you also need to know where the leak is, to the cylinder. A vacuum gauge on the manifold will not help in identifying a local leak.
Aye, I recall and have done the latter. A crude means of water injection Enables the engine to burh the carbon deposits. Huge CAVEAT !! TOO MUCH AND YOU GET HYDROLOCK. SERIOUS ENGINE DAMAGE!!!
Hooray!
Got my new intake manifold gaskets in, misfire on 4A is gone! In fact, car is idling smoother than since Iāve owned it!
Sure enough, the ecu fuel mixture was now too lean, so i enriched it, pretty much back to where its been for most of this year.
I need to test drive - double check TPS, throttle linkage, idle rpm and ecu mixture, as everything was out of spec after replacing intake manifold.
Test drove, felt nice and smooth. Even my poly trans mount doesnāt feel that bad now. Throttle response is more precise. Overall power about the same as before.
So i guess my intake manifold gaskets needed replacing?!
3 Likes
Also wanted to mention, ECU fuel mixture voltage output is almost identical now between A and B banks, 0.05V difference! Before, it was about 0.1V. With the misfire, the difference was 0.3V!
Good observation ! ā¦and good troubleshooting tip.
Makes absolute sense.
So, have you concluded that you had a vacuum leak at the intake manifold gaskets?
An accurate diagnosis requires a patient who can relay accurate and complete information and then the ability of the Dr. to have enough knowledge and differential diagnostic capability to sort thru the possibilities, ruling each out one by one, using symptoms that either fit or donāt. Iād say you did well on the first and the collective group, including yourself, did well on the second. Vacuum leaks as a result of failed intake gasket. A vacuum leak was my choice back 3 weeks ago. I also like watching the TV series House. Keeps the brain active. SD Faircloth
3 Likes
I think House always took about three shots before he nailed it. I guess itās lucky that Jaguars cannot catch Lupus.
Liked House. Great show. Would have been better with him driving a Jag 
1 Like
Trained mechanics rival the ability of top docs, during the differential part of diagnosis.
We get/got paid, not by knowing each and every issueā¦but because we knew/know where to smack itā¦