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Ask Ricardo Hohl Your Own Question
Ricardo Hohl
Ricardo Hohl, Master Certified Tech
Category: Chevy
Satisfied Customers: 4204
Experience:  Automotive instructor at Porter and Chester institute
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Cold engine 19 in vacuum warm 12in slow decline in inches

Customer Question

cold engine 19 in vacuum warm 12in slow decline in inches engine changes pitch when warm seems to loud up then a few seconds later cleans up some
JA: How many miles are on the car? Is it an automatic or a manual transmission?
Customer: reman from local shop auto trans
JA: What is the make/model/year of your car?
Customer: engine 96 5.7 vortx
JA: Are you fixing your vehicle yourself? What have you tried so far?
Customer: fix myself ck replace map replace dist cap/roter with engine pcv engine temp egr valve tps ign coilwith moduel oil presure switch
JA: Anything else you want the mechanic to know before I connect you?
Customer: replace catveter fear of clog / restriction
Submitted: 2 months ago.
Category: Chevy
Expert:  Ricardo Hohl replied 2 months ago.
Hi welcome to just answers my name is***** see you replace a number of parts and still having the same problem, are there any codes stored on the engine? Is your engine compression good any lost of compression through the intake valves or pcv will drop your vacuum haw menu miles on this engine?
Customer: replied 2 months ago.
Engine has only a few miles sence rebulld I disconect driver vide o2 senser and can drive car ! with conected no power after warm will not pul itself down the street. I am at home with no scanner I I fear the o2 is retard timming loss of power I have varried the timming (graduel move dist to compensate but moving the dist _+ or - not increase vacuum on warn engine . with o2 disconnect no loss of vacuum warm engine compresion 105 to 115 all cyl Vacuum gauge vvery steady no pounce as if valve not close adjust to 3/4 turn after clack warm
Expert:  Ricardo Hohl replied 2 months ago.
Does it runs ok when is cold?
Customer: replied 2 months ago.
ENGINE COLD SOUNDS OK backes up in drive way but will stumble to drive forward .no power on powerstall (brakes /gas same time) tries to power up but just gets worse to lungeing louping as if going to die.
Expert:  Ricardo Hohl replied 2 months ago.
I notice compression is also low you should have 150 and up, are you opening the throttle wide open when doing the compression test?
Expert:  Ricardo Hohl replied 2 months ago.
You have not mention fuel pressure is good?
Customer: replied 2 months ago.
no open throttle i was by myself for compression test I have good pressure and great valume I replace electric pump and replace presure reg 60 lbs Presure reg not leak but unsure after warm enginre relace map for same reason replace knox sensor but still same problem until i unhook right side (driver) 02.
Expert:  Ricardo Hohl replied 2 months ago.
it runs good with the right upstream 02 sensor disconnected, you did replace this side 02 sensor right? ok let me look in to this and get back to you today ok thank you for been patient
Customer: replied 1 month ago.
Richard cking in any info for me : have you come up with something? not tryng too push Also i have a 1998 hombre that does not down shift soon enough for a 4cyl any way to adjust ! . seems to be getting worse over time (downshift) at slow speed to increase speed without going to almost full petal thank you Tony
Expert:  Ricardo Hohl replied 1 month ago.
Ok when you disconnect the 02 sensor the computer sees it as a full rich comand and makes injectors run rich that's why the vehicle runs better. The fact that you have less then 12 inches of vacuum this can cause the map sensor to affect timing . Are you share the timing on the distributor is where factory wans it to be?. Can you install a vacuum gage and verify how much vacuum you get when adjusting the timing to factory specs.
Customer: replied 1 month ago.
I took the car to a shop with scan tool and they set timming to o+ - no improvement i am sure the map is the reson the vacuum drops because the vacuum drops on any engine if timming is slow right? I dont know what causes the timming / I tIIslash vacuum to stay with added fuel (rich comand) . what changes on warm up with 02 connected for the timming to change and thus lose vacuum /power. The shop had to change cam sensor to get signal to read /adjust time. I have a vacuum gauge on all the time1 Dist slight movement does not change vacuum 02 distconnected Just cking to see if i could confuse map/ ecm When engine warm 02 connected vacuum low does.not improve with slight dist move These problem with timming @ 0 for sure. fresh fuel new Iridium spark plugs Tony(###) ###-####
Expert:  Ricardo Hohl replied 1 month ago.
Well like I said the map sensor is affected by low vacuum causing timing to retard and fuel to increase . But all this is cause by low vacuum you need to find out why vacuum is low there are maenyWell map sensor is affected by low vacuum the problem may not be the map sensor because is there just to tell the computer when there is low vacuum cause by the presence of pressure in the manifold so replacing the map sensor may not work. What you need to do is find out why vacuum is low, you need at least 14 inches of vacuum for a map sensor to be effective. There are a number of things that affect vacumm like timing chain not correctly align, valves not seated properly to their valve seats and leaking pressure in to the intake manifold, low engine compression, intake manifold leaking vacumm, low RPM,s engine misfires, EGR staying open at idle. You need to check them all one by one a process of elimination, believe me if you have low vacumm this has nothing to do with the sensors this is a mechanical problem.
Customer: replied 1 month ago.
Ihad the heads rebuilt @ machine shop replace guides to insure no problems now or later (years later) I remove plemtum inspect o ring /replace. EGRvalve not stuck I can push it open it spring close. I spray start fluid all along manifold to search vacuum leak. include throtle body Much time spent looking for vacuum leak. Engine rpm set by tps engine rpm higher on start but quickly returns to normal rpm. E ngine sounds good cold no misfire very good throttle response no vacuum leak can be herd useing small hose into y one side in each ear I know it sounds like vacuum leak but what if there is no vacuum leak. what effect would i notice if i unplug map so it would not see increase in manifold presure. any way to confuse map so it would not do its job. would i have good vacuum cold if timing chain one tooth off ! how can i tell if off. i cked valves closed TDC would timming set (coralate) cam /crank if chain off then change on warm engine to loose vac
Expert:  Ricardo Hohl replied 1 month ago.
Is this a Chevrolet Suburban or GMC truck
Expert:  Ricardo Hohl replied 1 month ago.
Are there any codes on the engine cam and crank sensor or any other codes that where not created by you like the 02 sensor disconnected?
Expert:  Ricardo Hohl replied 1 month ago.

Disconnect the CMP sensor.

2. If the engine runs good at that point, remove the distributor rotor.

3. Check the top of the vane cup for a "6" or an "8". This is not the "8" or "6" that the distributor is aligned to during installation.

4. If a "6" is present, the wrong distributor, one for a 6 cylinder engine has been installed in this 8 cylinder engine

Expert:  Ricardo Hohl replied 1 month ago.

if the distributor is correct then only thing there is valve adjustment to tight you said 3/4 is to much you should do 1/2 the most and see what happens to much will increase pressure on the intake and drop vacuum. make sure you have a vacuum gage attach so you can read vacuum as you doing it.

Customer: replied 1 month ago.
This engine 96 1500 chey pu complete w dist I will readjust valves again if you think i should , maybe sat morning ,to1/2. I did use vac gauge the times before to watch for bounce then settle to smoth netle to make sure no valves sticking or to slow to settle down!! I will need to return to shop to read codes How will i know if cam one tooth off, what will i look for as you sugested early.
Expert:  Ricardo Hohl replied 1 month ago.
You should have all the sprockets on the cam shaft lining up with the links on the chain I will send you the set up tomorrow from my job. And yes if your valves are to tight then vacumm will be low, try readjusting valve and try getting the highest vacumm you can get. Let me know before you start on Saturday in case I come up with other ideas instead ok.
Customer: replied 1 month ago.
Thanks Ricardo ?is there a symptum i can look for without remove front cover , balancer, oil pan ect to ck chain links ect let me know tomorrow
Expert:  Ricardo Hohl replied 1 month ago.

do not remove the timing cover yet lest confirm with the distributor first put the engine to top dead center on compression stroke then remove the distribuitor cap check the position of the rotor is it line up to #1 cylinder?

Expert:  Ricardo Hohl replied 1 month ago.

and if it is then get your self a vacuum gage let the engine worm up read vacuum is it less then 14 inches ?

Customer: replied 1 month ago.
I put tdc on compresion and remove cap. roter point to #1 on dist cap. acording to picture in moter manuel in proper place in general This cap has fire order on cap .( odd looking cap for that engine) ! timing set @ shop with propper tools. +- 0 Engine starts with vacuum gauge @ 18 +in Warn below 14 in
Expert:  Ricardo Hohl replied 1 month ago.
Ok, are you getting any codes for a map sensor? Or 02 sensors?
Customer: replied 1 month ago.
I took my car back to shop with scantool but it will be tuesday before they can scan and i find out other codes. now i have another problem # 7 cyl dead no pulse from spider what senser would stop fuel to one cyl
Expert:  Ricardo Hohl replied 1 month ago.
Sensors will not turn injectors individually, but the pcm computer will if it sees a problem with the injector or if you loose spark on that cylinder cause by spark plug, or coil, check for spark first see if is present. Then check resistance on the injector and if ok then do a compression test on that cylinder you should have over 150psi