Compressions/Leakdown Test results

[calciumdust]

Greetings! This website/forum has been an incredible source of knowledge and expertise. Thank you to everyone for being a part of this community!


I recently purchased a Geo Tracker, 96, 16v M/T, 160k miles, southern car, countless previous owners. It was somebody's converted huntin' rig and had the deer blood stains to prove it! I purchased it in a barely running condition. It would idle roughly, but die if given more than 10% throttle. The PO had put in a new fuel pump and replaced the MAP before giving up on it and selling it to me. I planned to do a full top end rebuild given the spotty maintenance history and picked up all of the gaskets/belts I would need to do that. 

The fuel pump had been improperly grounded. Once I fixed that it ran rough, but did not die under throttle. It smogged heavily however. OBD2 scan revealed the TPS was faulty, I assume the smog was due to it being in limp home mode. The TPS is stupid expensive so while I saved up for that part I set about doing the top end rebuild. Fel-pro gaskets and a Gates timing kit. Removed the head, gave everything a good clean. Removed and replaced the crank sproket to check the crank key. Everything was looking good. Checked the head with a decent straight edge, but did not send it to a shop. 

Reassembled everything and put the new TPS on it but could not get it to start. Spark/Fuel pressure was good. Did a compression test and got the following.

Dry
1-115
2-163
3-110
4-128

Wet
1-115
2-171
3-120
4-148

I then did a leakdown test on each cylinder to identify the problem areas:

1 - 80% loss, leaking from crankcase
2 - 10% loss
3 - 45% loss, leaking from crankcase
4 - 50% loss, leaking from crankcase

The Dry/Wet compression tests showed improvement in some cylinders but not all. Speaking about #1 specifically, would a massive gap in the piston rings prevent a wet test from improving compression? Or am I missing something on the head. 

I'm considering sending the head out to be more thoroughly checked but the local shop is $325 for a crack check, pressure check, and a resurface. If the valves are an issue I'll be spending more than that. If I also have to do a bottom end rebuild I might just start looking for a new engine.

Thank you in advance!

[fixkick]

Greetings! This website/forum has been an incredible source of knowledge and expertise. Thank you to everyone for being a part of this community!


I recently purchased a Geo Tracker, 96, 16v M/T, 160k miles, southern car, countless previous owners. It was somebody's converted huntin' rig and had the deer blood stains to prove it! I purchased it in a barely running condition. It would idle roughly, but die if given more than 10% throttle. The PO had put in a new fuel pump and replaced the MAP before giving up on it and selling it to me. I planned to do a full top end rebuild given the spotty maintenance history and picked up all of the gaskets/belts I would need to do that. 

The fuel pump had been improperly grounded. Once I fixed that it ran rough, but did not die under throttle. It smogged heavily however. OBD2 scan revealed the TPS was faulty, I assume the smog was due to it being in limp home mode. The TPS is stupid expensive so while I saved up for that part I set about doing the top end rebuild. Fel-pro gaskets and a Gates timing kit. Removed the head, gave everything a good clean. Removed and replaced the crank sproket to check the crank key. Everything was looking good. Checked the head with a decent straight edge, but did not send it to a shop. 

Reassembled everything and put the new TPS on it but could not get it to start. Spark/Fuel pressure was good. Did a compression test and got the following.

Dry
1-115
2-163
3-110
4-128

Wet
1-115
2-171
3-120
4-148

I then did a leakdown test on each cylinder to identify the problem areas:

1 - 80% loss, leaking from crankcase
2 - 10% loss
3 - 45% loss, leaking from crankcase
4 - 50% loss, leaking from crankcase

The Dry/Wet compression tests showed improvement in some cylinders but not all. Speaking about #1 specifically, would a massive gap in the piston rings prevent a wet test from improving compression? Or am I missing something on the head. 

I'm considering sending the head out to be more thoroughly checked but the local shop is $325 for a crack check, pressure check, and a resurface. If the valves are an issue I'll be spending more than that. If I also have to do a bottom end rebuild I might just start looking for a new engine.

Thank you in advance!

I compression test done warm or hot , hot = 180f (we do it warm, so now hot hands worked) and at WOT, if the throttle is not blocked open (fuel pump relay pulled)
there may be no air to pump, (IAC is only source and is only a source over 150f water temp) so never do compression with throttle closed, open it a tad to full)
let the needle peak, do not count crank turns, let it peak. (it will do that  in say 3 turns) battery fully charged and good, (im sure you know that)but others may not.

so the head was pulled and ,new head gasket put down, felfpro is good.?????
with head off and now rockers are free
the valve 16 valves must not leak ,now, the classic DIY test, is invert the head, and fill each combustion chamber 1/2 full of say paint thinner. and it must not leak to the ports. (even a new head will not leak gasoline tired)<<< the latter is fume and fire danger. (in shops they have fire proof solvent to do this test) Brake cleaner? if minor leakage the valves can be hand lapped in.

compression test:
the cylinders are fully round warm+ and not cold. (ring leakage happens cold)
but is a moot point the valves are bad. wet fails. as does the leak down prove fail and moot too. (but gee cracked Piston rings, or fully carbon packed up and compressed will fail all tests) but wet tests on good piston ring only worn do seal up wet.(normal wear that the carbon horror, running in limphome for 10 years. black smoke at the tail)

is lash at spec?
or someone set lash all wrong using the wrong way of 2 possible.  (suzuki book way and the classic, both cam lobs on the heels is closed valves for sure)
also the rocker keepers ID6 love to fall out as the there tiny springs  (horseshoe spring) fail.  (they crack) and ID11 are now hard to buy (source) or missing.
part ID 11
http://fixkick.com/engine/96-98%2016v%20...ngine5.jpg




Good luck on this motor.

[fixkick]

check rockauto.com for parts ,see brands and p/n there, yes TPS can be hard to find. http://fixkick.com/buy-parts#TPS
the FPR is bad on most of these cars. this old.
fuel pressure reg.
use a scan too (any OBD2 tool made works (USA car, 1998 canada car up)
see errors, you will if in limphome.
all DTC are listed at fixkick.com (search DTC) see em.

[fixkick]

yes the piston rings do fail. if head off, you see a slab of carbon thick top of piston
the engine was run in limphome forever.
or FPR was bad and ran rich as a pig forever. idle PSI is 10psi less than WOT, PSI, when failed if PSI is at WOT pressure all the time the FPR is stuck closed.
the carbon progresses to the lands. (piston)

and packs the rings up. and they sure can stick compressed and leak bad.
is the CAT missing if not the rich conditions make it glow RED hot and melts it and no engine power like that.

[calciumdust]

Thank you for the tips. I found a decently priced head check in town and got it resurfaced/cleaned etc. Got it running and compression is great on all cylinders! I leave this as a warning to other frugal (or cheap) home mechanics like myself. Just spend the money and have the professional look at it!

Currently I'm struggling with heavy smog while running, all plugs are getting equally blackened so I don't think it's one injector sticking open. Fuel pressure is 35 psi at idle. I did a lot of poking and prodding and finally noticed a cracked exhuast manifold on cylidner #4. Assuming that's tricking the O2 sensor into running rich. On the hunt for a new one or a fix and I'll update once it's replaced.

[Diennuocanhquan]

Thank the author for sharing this useful knowledge!

[fixkick]

yes the valves were bad but expected on any car this old.
ok its running rich as a pig. black tip spark plugs
so the scan tool dead. no DTC errors no check engine lamp on key on the goes out running????????????
16v engine the exh man stock loves to crank it does that in limphome mode easy, it gets too hot.
yes it sends 20% oxygen to the 1% max o2 sensors and it slamps to 0v and goes rich.
scanning the ECU with scan tools (real) show PIDS for fuel trim crazy high fuel.
and looping and graphing the 02 front shows it slammed to 0vdc. and does not swing say 6 times a second, that is hard failure for closed loop and the tool shows stuck in open loop. mode OL (not CL)

yes finding good new manifolds is not easy , i got one of the last ones ever. from suz. direct.
is this calif. smogged? CARB (air research board) tested?
if yes , they will reject any aftermarket exh manifold that is not CARB sticker certified.
but no state told and matters huge on cars this old
my 95 jeep is free of smog tests in TX.

the cat on the 1996 is called 3 way cat
and the 02 must work and swing correctly
and EGR must work or NOX fails.
28 year old cars many states do not do smog tests after 25 years old, so few left running it is not on theIR RADAR.

you can even drive the car with 02 front pulled and see it go way leaner and MPG goes WAY Higher.
UNPLUGGED IT FREEZES AT 0.45 VOLTS AND IS mid point.
hey good luck to you, hope it gets better soon.

[calciumdust]

I did some driving around today with a scan tool running and recording.

Only code was a P300, misfires detected, which makes sense as it is misfiring at idle, it smooths out at higher rpms but is never perfect.

The STFT was -25% at idle, and apprached 0 during acceleration, which makes sense given the smog, no question that it is running very rich. Does the very low STFT demonstrate that the ECM is receiving proper data from engine sensors and determining that the fuel input need to be reduced? Therefore should I start testing injectors? (fuel pressure is all within' spec, FPR is functionign properly)

I'm seeing zero movement on LTFT, is that normal?

O2 sensor stayed around 0.9v, which makes sense given how rich it is running. I didn't get much movement on it either. It would periodically drop to near 0 volts and then back to 0.9v. It did not swing back and forth multiple times a second. Is that a symptom of a bad o2? The high o2 sensor voltage also makes me question my theory that the ex manifold leak is causing the engine to think it is leaner than it is. If that was the case wouldn't my o2 sensor have a much lower voltage?

If I pulled the front o2 and the car ran better would that indicate the o2 is failing?

Thank you for the advice! I'm still going to seek out a new ex. mani but I want to be sure that's my only problem.

[fixkick]

You forgot Closed loop status word (PID)?
does it do in light hot cruise.  it must hold closed loop , if not and is in open loop  fuel trim is not on line , accelerating or at WOT>
only idle and light hot cruise.
seems the ECU is in limphome.
on a 1995 car it would be 10x more rich then horrible rich, in 1996 this effect was greatly reduced OBD2.
Id fix idle first. if not in close loop then (hot engine) fix that, as  car is parked and x10  more easy to fix any Parked car. and safer too.
in closed loop the PID scan and graphing (plot mode) of the front 02 it swings 6 times a second, this is the ECU hunting perfect combustion.
exh leaks any where near the 02 front is doomed to kill the 02,  and goes HORRIBLY rich, unplug the o2 and now 0.45vdc is hard fixed at 02 ECU input pins, (a voltage divider magic thing)  that will make it go learner, but not go closed loop like that, no 02.

no pulling the the 02 only shows it is too rich not way,  lots of why's for sure even a bad engine, dead maf,  or weak maf,
fuel pressure is good 31psi at idle  right?
wrong p/n injectors not on the engine right?
injectors cushions (base side at intake manifold) not sucking air.
p0300 is all 4 cylinder random misfiring, (means combustion is weak,  random) on all 4. (engine weak, fuel bad or spark bad caused)

that -25 STFT , my best guess, is old data stuck there not live at all.  it is  GHOST of the past.  (seen it I have)
learn to read the CL/OL  status PID first,  OPEN loop is fixed first. OL

the 16v,  take off the exhaust manifold shields yet see #3 cracked  as  they all did,  when driving with CEL glowing for 50,000 miles, and cheap #2 gas.? Lol

fix idle first
fix closed loop dead.
parked.

if injectors are good and pressure good at idle,  injectors can be pro cleaned, so they do no leak and full flow returned.
make sure the MAF is not dead/weak, (my MAF page shows the simple tests using any DMM )  i tested the snarf out of many to get the data seen here.
do know this the ECU does not report weak maf only the DEAD.
we do now the idle volts out.  for sure

more tests not done, scans for PIDS do them. even log them and share them is no better thing to do.
ECT reads what hot,  180 to 200f is the answer never 150 or OMG less with silly fail safe thermostat stuck in lame , failed mode. yah a pain.

YOUR MAP READS WHAT AT IDLE?

https://fixkick.com/sensors/92-95MAF/92-...sting.html

(exact specification is 1.7–2.0 volts) at idle !!!,  gunned it goes to 3v. (only flogged up hill hard will get max maf readings , I had to drive an log to see it) https://fixkick.com/sensors/92-95MAF/hills1.jpg

SEE MY GRAPHS THERE,  DRIVING AND PLOTTING MAF,  AND TP SENSOR SAME TIME.

MAF is a chicken and egg device, if weak  there will be no power from the engine seen at the high end of the maf .... (well if not stuck in limp home that is)

Your post did not tell how much power the engine had . now.
new head.
if the cat melts the power will be horrible even 20 mph limited
even dead. (as it melts more)
and vacuum gauge attached, the vacuum seen (needle) is all backwards and crazy, due to engine can not pump air now, cat melted and blocking 1/2 or more.

if you have full engine power (or as good as it can be rich) then CAT is ok.
the engine going rich the CEL flashes at you driving
the flash means the CAT IS SOON TO DIE (melt) even says in the book drive easy no tailer pulls and get  it fixed fast. (and is truth)
P0300s do that
the PCM knows fuel mix is rich and burning outside the engine, like rock engine, and all that unburned fuel extra burns the cat up and cracks the Exhaust manifold
just under those old cute shields, if still there. mine were.
my 96 day1 to me, I found mine cracked. (this also packed up the EGR full of carbon ,look like a wall of carbon)

good luck there are some tests there to do.
It can be fixed that is  for sure.

your 02 front may be poisoned now.
some can be recovered with propane torched to the tip. burning off the carbon.

your  ECU can not wake up the 02Front,  and most times its not the 02 fault. 
most times a bad 02F is just the heater is dead. super common fail that is.
my 96 would go closed loop fast, the 02 got hot and works correctly and swings, and CL sets in the PID status, fast.  I bet yours is dead CL !
even not at 180f yet it gains CL, it may do it just past 150, as 150F is the threshold of the IAC, valve, thermal fast idle closes at 150f.
OBD2 wants to get CL fast as that saves fuel, smog and and then engine,lasts longer. and CAT lasts longer too.

[calciumdust]

Got some time to work on it today.

I checked the MAF per your instructions.
-Blue/Black wire was 0.1v lower than battery voltage. Is this within tolerance? (12.3 v vs 12.4 v at the battery)
-Grey/Black wire was 1.623 v at key on/no start and 2.4 v at idle, it idles around 1200, I can't get it to idle lower. Voltage increases to 3v when racing the engine.

Fuel pressure is right at 31 psi at idle. It responds correctly to the throttle body vacuum line.

ECT was betwen 170-180

When I drove it around it felt a bit sluggish but not any worse than I could expect with it running so rich.

Still no o2 sensor swing, it just hangs out around .9v? Which indicates open loop right? Which means the ecu is gettign some signal it doesn't like, so it's not even taking the o2 sensor into account? Is that a correct reading?

Given that it has correct fuel pressure, I checked the resistance across all the injectors, they are all good to go. What's my next step to rule out any injector issues?

I've sourced a decent exhaust manifold and I'm planning to swap that out soon. I hope that's the big issue that solves everything.