Isuzu SUV Forum banner
41 - 60 of 63 Posts

·
Registered
Joined
·
9,708 Posts
aidan7777 said:
i get vacuum at the FPR on a cold start.
You SHOULD have vacuum on the FPR on a cold start (or any start). Some have hooked the FPR vacuum hose directly to the plenum chamber, and theirs ran okay that way.
What you DON'T want is vacuum to the EGR valve on a cold start and be sure your EGR transducer is working and plumbed properly. If you suspect you have an EGR issue, just unplug the vacuum hose at the EGR valve, plug the hose, and see if that makes a difference. Dennis
 

·
Registered
Joined
·
132 Posts
Discussion Starter · #42 ·
Fair enough. Most cars have constant vacuum to the FPR, anyhow.

Here's the thing, though. I don't HAVE an EGR. Either it wasnt standard equipment here in the first place, or it was removed when the calmini tri-y's went on.

One of my EVAP lines is going straight to the T joint on the end of the throttle body line, though. something's clearly wrong with the way this system is routed, and that single vacuum switching valve only makes me more suspicious.

I'll see if i can find a proper VSV from a wreckers yard up at my dad's place. If not, I have a terminal crimping tool and a wiring diagram, Any pair of valves from any make and model will do.
 

·
Registered
Joined
·
132 Posts
Discussion Starter · #43 ·
Checked spark plug wires today. I see a little cut on one, and long flat spots on the rest where the cables have been rubbing on things, but when i bend them around with the multimeter hooked up, I dont see the needle fluctuate. around 2 to 2.5 kilo-ohms per wire. None of them show conductors.

Only trouble is they fit sort of loose on the plugs. The wire on #3 is noticably looser than the rest, and has a distinct bend in the spark plug boot, like somebody stepped on it or something.

Just ordered a compression tester and a neat little chinese boroscope. When i get back from dad's place, i'll post compression test results + photographs of the combustion chambers and valves.

If i do find a burnt valve, I don't think i'm going to throw away this head. the rest of it is in really good condition.
 

·
Registered
Joined
·
132 Posts
Discussion Starter · #44 ·
Oh yeah, one piece of information i forgot to add earlier, if its of any use.

My dipstick keeps popping out, and the PCV valve on the top is wrong. its port is differently sized to the corresponding port on the plenum.

Can that cause problems with the vacuum system, or not? apart from plug wires, i am completely out of ideas.
 

·
Registered
Joined
·
132 Posts
Discussion Starter · #45 ·
Sorry for spamming up this board, just want to make a quick update on where i'm at right now.

I made a little homemade smoke machine out of a glass jar, a piece of hose, and an old schrader valve from a dry rotten inner tube. Lit up some shredded cardboard in there, made it smolder, then hooked up a little 12V air compressor and went to town.

That intake had more smoke in it than cheech & chong and i still couldn't find anything. both RUN and ACC gave me pretty much nothing at all.

The only smoke that came out was from the throttle body. Couldn't get that sealed perfect, even with tons of layers of glad wrap AND a nice tight constrictor knot. (i had so much pressure that the elastics kept blowing off). Didnt see smoke coming out of anything else at all.
It was well in the little hoses. pull one off the top of the FPR and it would BILLOW out.

It's got to be either misrouting (as i said before, the hoses do NOT match up with the diagrams), a leak in the PCV line, a result of it having the wrong PCV valve(even though it rattles. i can still suck a fair amount of air through the barb side, though.), or something very very serious. I have a reading of 17-18 in/Hg at 3500 feet, which should be well within the normal range.

EDIT: Just replaced a dodgy homemade cap on the intake with a proper rubber plug. It was an old battery terminal connector over a coil of tape tightly wound over the outlet, sealed off with a screw clamp. I dont think it'll help, but if not, it'll at least rule it out.

EDIT 2: It didn't
 

·
Registered
Joined
·
9,708 Posts
aidan7777 said:
Sorry for spamming up this board,
NOT! This is EXACTLY what this forum is about - helping people solve problems. There have been "problem child" problems that were SEVERAL pages long.
Now. First on the PCV - try just removing the valve and plugging the hose. This should give you a lower, rough idle.
Another thing. After re-reading this entire thread, I have to ask (suggest) are you absolutely sure the timing belt timing is right. A tooth either direction and they can run, but have all kinds of symptoms. It really isn't difficult to check, just the top cover and align the mark (if your balancer is still accurate (crank should be at zero). Just sayin. Dennis
 

·
Registered
Joined
·
132 Posts
Discussion Starter · #47 ·
Thanks, dennis.

I removed the PCV and just capped off the port yesterday, the high speed misfiring seemed to subside, but that could be because the engine wasn't stone cold. the issue is at its worst on a cold start. idle really didn't seem to change, still had an erratic 500rpm dip on high idle.
It's obviously the wrong valve. the barb is a different size to the port on the plenum. god knows how wrong the flowrate might be.

Timing, huh? i never would have thought of that, I'll check the timing today.
My balancer is seriously out of whack, though. will that be a problem, or no?

I remember getting this car to run well by spraying oil down the IAC line a few years ago, can't imagine what might've happened in the meantime. crank angle sensor still dirty? i couldn't get the sensor wheel off because the screw stripped.
I'll run another smoke test, too. this time i'll plug up the throttle body extra tight. Vacuum leaks still aren't ruled out.
Can misrouted hoses do the same thing as a leak? i've been having no end of trouble finding them.
 

·
Registered
Joined
·
1,375 Posts
You've Mentone a few times that the vac diagram doesn't match, but have you put any effort into trying to connect them the way the diagram shows? I assume you have, but thought I'd ask.
 

·
Registered
Joined
·
132 Posts
Discussion Starter · #49 ·
I only had one VSV for some odd reason, so I can't match the diagram in the first place. The EVAP canister line goes straight into the T on the end of the hose coming out under the TB instead of going through a VSV with a 'hat' on one end, but crimping that line doesn't seem to do any good.

The problems only really seem to manifest at high and low idle, and intermittently around 2500 RPM as a misfire. but above that everything runs just fine. I took it to 6000 on a test drive and it didnt complain about that at all.

The single VSV i DO have matches up just fine with the diagram, but the fact that i don't have another one on top is what's bugging me. Everything else seems to match ok.

I broke off the straight part of the "T" while i was taking it off, What looked like a nut holding its bracket onto the wheel well of it was actually a captive one, and i thought it was siezed, so stupidly, I put some muscle into it and broke it. Never work angry..
Can't find the piece anywhere on the floor, so it looks like i'll be buying one anyway. In the meantime, i'll route the fuel pressure reg straight to the intake plenum and run it that way if i need to do work around the property.
Despite that, i put it on my test bench and put power to it, it clicked, so it was working fine before i screwed it up, but the thing that interested me was the way it directed the airflow. powered off, it directed air from the 'bent' section of the T to the line behind the solenoid, and powered on, it directed it from the bent section to the plastic line INFRONT of the solenoid which i broke off.
This would give the ECU the choice of taking vacuum from either the intake manifold itself, or the port underneath the throttle body that goes into the T fitting. (NOT the one that if equipped, would go through a thermal vacuum valve, then through a back pressure transducer. word has it those ports have different characteristics of some kind.)

I don't understand what difference it would make. everything behind that butterfly valve is under the same vacuum, isn't it? is there something special about that particular port?

I also ran another smoke test, still didn't find anything. but there was smoke leaking out the top of the dodgy jar setup i was using, so maybe that could've covered something slight.
And as for timing, i'll have to take a bunch of things off to remove the lower part of the cover. Need to rely on both the timing mark up top and the one on the crankshaft pulley if i want to make sure everything's right.
The belt IS tracking a little to the side facing the engine, though. I don't know if that's bad.

All in all, thanks for the suggestions. each and every one counts, as i really don't know where to go next.
 

·
Registered
Joined
·
9,708 Posts
Is your truck a NON air conditioned one? Dennis
 

·
Registered
Joined
·
132 Posts
Discussion Starter · #51 ·
No, it's air conditioned, but it doesn't have the little AC idle solenoid.
Do the manual trucks not have that one?

I also noticed my throttle body has a little up and down play. I know worn throttle shaft is a classic area for vacuum leaks, but for whatever reason i didn't see any smoke come out of it.
Then again, my setup wasn't exactly the best way of doing that test.
 

·
Registered
Joined
·
132 Posts
Discussion Starter · #52 ·
Alright. i know i've replaced absolutely everything rubber and gasket related on the intake, but I swear to god i must still have some kind of crazy vacuum leak. Should i be getting 22 in/hg at 3500 feet? (Hey DSUZU! How high above sea level are you? From what i've seen your 22 in/hg seems to be the gold standard.)
Disconnecting the big hoses on the intake doesn't raise the idle or change the running condition of the car. nor the little ones. This 2500 RPM misfire only turned up AFTER i'd replaced the intake manifold gasket, so who knows. maybe i got it misaligned during the install and ripped it? I do see a part of the gasket sticking out from behind the flange, so it's a possibility.

Besides. maybe the gasket set was crap in the first place.They wanted 30 bucks for that stupid thing when RockAuto had a proper fel-pro for only 3 dollars AU, and the thermostat housing gasket i got in the pack they sent me weakened and tore after one cycle, like it got saturated and crumbled away.
The throttle body upon further inspection has a little side to side play, and only very slight up and down, but surely a bad throttle body'd have much worse wear than that. Is there o rings in there?

It doesn't seem to return to idle too quick, It starts trying to die off after 30 seconds to a minute of running, I have checked everything on the ignition side to no avail,
This thread also says that no idle + running as long as you give it gas means vacuum leak. https://forum.planetisuzoo.com/viewtopic.php?p=5309626

I'll end by posting this video again, it shows exactly how this car behaves at idle, as well as how long it takes to return. does this behaviour look like vacuum leak to any of you guys?

It's trying to rest at around 1000, Could probably chalk that up to the idle mixture screw being out too far, but I don't think it has anything to do with this.
a misadjusted screw SHOULD steadily go down and down as the air reg (IAC) closes until the engine dies, not waver its way down while popping out the exhaust.
And on top of this. wrapping the screw in teflon tape did not help the issue. The o ring is a little worn, but it doesn't have any compression set nor any nicks.

I have also not tested fuel pressure, but again. the car didn't complain about going 6000 RPM at WOT. Only weird thing is if i suddenly punch the throttle, the engine hesitates for a split second before revving up, but if i ease it in, it revs up just fine. I only bring this up as i found a video by this gentleman who seemed to be having a similar issue to mine, except his car bogged down completely at WOT.
Johnny-5 said that it sounded like his fuel pump was bad or the filter sock was clogged up. (damned if i know how a fuel pump can go bad without burning out.. cavitation? seals? voodoo?)

I will be going up to my father's place very soon and will be staying for a few months, when i come back, i'll have a compression tester and boroscope with me i can use to inspect this engine. considering all cylinders have healthy looking crosshatching, the car doesn't smoke, and the engine has only really done 20-30,000 kilometers since its rebuild, it should be roughly around 170 PSI for all of them. Will post the results here when the time comes.
 

·
Registered
Joined
·
9,708 Posts
aidan7777 said:
(Hey DSUZU! How high above sea level are you? From what i've seen your 22 in/hg seems to be the gold standard.)
I am all of about 16 feet.
Note that the 22" was with a fresh rebuilt engine. The tighter the engine, the better the vacuum.
An "IDLE AIR ADJUSTMENT SCREW" - the big slotted screw on the top rear of the throttle body (please tell me you haven't messed with the idle stop screw (on the shaft). Any way, idle air screw turned out too far will be very high idle (vacuum leak)
Worn throttle plates or bushings will cause vacuum leaks - would not show up on a smoke test if your TB was capped (maybe shafts, but maybe not)
Leaky gasket (lower intake to head) could easily be bad vacuum leak
The engine should be able to run with ALL vacuum hoses removed / disconnected and capped or plugged. Most of the myriad of vacuum hoses are for emissions or accessories. The only one that is really necessary is the FPR, and even THAT one isn't completely necessary (note: for troubleshooting purposes only). Dennis
 
  • Like
Reactions: aidan7777

·
Registered
Joined
·
132 Posts
Discussion Starter · #54 ·
Thank you very much for the insight.

Figured you might've lived around sea level, Explains the difference between our readings on fairly fresh engines.

Fortunately, i have NOT been fiddling with that stop bolt. I've been playing with the idle air screw on the back of the throttle body just like you're supposed to. (dont know if a dastardly previous owner has, though.)
And as for the throttle body, I can see daylight through it when i have it closed even after cleaning it, and also have that little bit of side to side play. Could something like that have such an adverse effect on the idle?
(thanks for pointing out the plates and the smoke test thing, by the way. i thought it was just throttle shaft bushings i had to worry about.)

If it turns out to be that intake gasket. at least the job won't be as horrible as it was first time. I replaced the upper studs with bolts, so i can easily take it off in the future. (hopefully that isn't the cause of it all, i have them nice and tight, and the intake lines up just fine)
Trick i found to get to the lower bolts off the manifold was to step up into the engine bay, stick my hand all the way down the side of the intake like i'm delivering a calf, get cut by all the razor tipped zip ties, and work completely blind with a ring spanner. Using a 1/4 ratchet with a long extension works too, but the AC hardlines are always going to get in the way of at least ONE of the bolts..

If this turns out to not actually be a mystery vacuum leak, next place to look is the fuel system. I'll buy a fuel pressure tester. This won't be the last car i'll work on.
 

·
Registered
Joined
·
9,708 Posts
That "daylight" is probably your vacuum loss. While usually on carburetors, I have seen a lot of throttle plates that have "grown ears". Dennis
 

·
Registered
Joined
·
132 Posts
Discussion Starter · #56 ·
Go figure. You'd think seeing light come over the edges of the butterfly valves wouldn't be such a problem for EFI, seeing as it should be airflow that will be reported and accounted for by the MAF sensor, But i don't know very much about the oddities of these old systems. Maybe they only want you taking in extra air through that screw?

Will the post 1994 throttle body bolt straight onto a 1990 plenum? The airflow increase would be a nice bonus on top of finally being able to hold idle.
 

·
Registered
Joined
·
9,708 Posts
Air flow meter measures FLOW, not vacuum. When the throttles are cracked open, is when there is flow. Vacuum, really isn't monitored on this system, but it is still necessary for the running. The later throttle only fits the later plenum or upper manifold, that system also has larger runners on the lower intake and uses different injectors. They tell me that the earlier body actually flows higher.
Here's a thought: With it running, try holding your hand (or something else) over the air inlet on the air filter. See what happens. If possible, try partly blocking that opening when revving the engine. Dennis
 

·
Registered
Joined
·
132 Posts
Discussion Starter · #58 ·
Ah well, whatever performs better is what i'll choose to run. The earlier plenum looks way cooler with the graphics on the side, anyway! :D

I thought the air flow meter would account for the worn out throttle plates, as the intake seems to be the only place that air can come from to leak past them. (isn't that also how the screw on the back works to set the idle?)
But i have been wrong many times before. When i get back to it i'll try partially blocking up the air filter, alongside a few other things.

Thank you very much for all your help, i've learned a thing or two about EFI.
 

·
Registered
Joined
·
132 Posts
Discussion Starter · #59 ·
Alright, i'm back. I've got a compression tester, a boroscope, a fuel pressure tester, and starting next week, a job.

Will be posting my results sometime soon. thinking this might actually be a problem with fuel delivery, not vacuum.

Having a look at my "tach 2" video, it seems like the RPMs hover around idle for a bit, start wavering a little, then suddenly drop off a cliff. This makes me think there may be a problem with the fuel pump circuit that's cutting power to the fuel pump, or giving it intermittent power at idle, and the engine continues to run off the residual pressure in the line + ECU compensation until the condition gets to the point it cant hold the idle. The pump itself is more than capable of supplying enough fuel for full throttle running, so i'm not going to point fingers at that just yet.

The only two things that are supplying power to its relay coil are an oil pressure switch, and some weird fuse that's hooked to something to the alternator, ostensibly to cut the fuel pump in a crash.

Both of these run through what looks to be a diode OR gate, which is housed in a little orange plug underneath the drivers side dash. you'd think an AND gate would serve better for that purpose, but maybe these are special diodes with a very high forward voltage, or whatever, that's the only way i can put it that makes any sense to me.

But since both of them are clearly responsible for powering the relay, that casts suspicion on the both of them, especially the oil pressure switch as it has a rubber diaphragm in it, and 30 years is enough time for them to fail.

I could go on, the only thing that can really prove this conspiracy theory of mine is my new fuel pressure gauge, so wish me luck!
 

·
Registered
Joined
·
132 Posts
Discussion Starter · #60 ·
Couple of worrying things came up with the tests.

The compression test looks to have confirmed my worst fears. I suppose i'm in for a valve job now.
If i can't do it myself, i'm at least going to save myself some labour cost by taking this cylinder head off first BEFORE i take it to a mechanic.
I will take borescope pictures and post them later.

#1 - 120 (!)
#2 - 165
#3 - 165
#4 - 160

And as for the fuel pressure test, The car would not start when i plumbed the test gauge into the system, and the pressure i DID get peaked at 32 PSI, and dropped down to 20 PSI within minutes.

If the system can't supply enough pressure to run a gauge on top of the regular fuel system, and the pressure leaks by that quick, that casts a lot of doubt on the fuel pump. (all 4 injectors were cleaned and tested, they're all perfect)

I feel terrible. but I've done too much with this project to give up now.
 
41 - 60 of 63 Posts
Top