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Dieselin tehot kateissa...
[03.09.2002]
Moro! Autoni on Caprice Classic ja siinä on 6.2D + TH700. Ongelma on moottoriin hiljalleen iskenyt tehottomuus. Kone kiertää kyllä hyvin ja käy tasaseen mutta jos lyö kaasun pohjaan niin auto ei sudi edes hiekalla. Sama juttu kiihdyttäessä, pirssiä ei tahdo saada ollenkaan kulkemaan jos on pienikin ylämäki. Polttoainesuodatin on vaihdettu ja mitään vuotoa ei näy? missä vika? Ps. koneella on ajettu 120tkm ja laatikolla 15tkm ja toimii virheettömästi eli vika ei ole siinä. odottelen innolla neuvoja kokeneemmilta harrastajilta!

Aktiivijäsen Liittynyt: 10.12.2003 Viestejä: 3669 Paikkakunta: Ylästö

Onko siis että kone reagoi kaasuun hyvin muttei voima välity liikkeeksi asti?
Luistaakohan laatikko siis niin rajusti?

Niin, kone P-asennossa ottaa hyvin kierroksia mutta vaihde päällä ei vain vedä! Eli siis turbiini ei luista vaan konetta vaivaa ilmiselvä tehottomuus. Muuten kulku on ihan normaalia mutta pirun laiskaa ja vika on ilmestynyt pikkuhiljaa.... en ole varma mutta olin kuulevinani pientä räpätystä kiihdyttäessä, mitä ei ennen ole kuulunut!!

Vakiokävijä Liittynyt: 19.08.2002 Viestejä: 678 Paikkakunta: Otalampi/Vihti

Onko ilmanputsari vaihdettu.Ottaako kone kierroksia vaikka ei kulje.Tämä aihe kiinnostaa mua.

Ilmanputsari on vaihdettu, kone ottaa kyllä kierroksia kun ensin vain jaksaa ottaa niitä! Menee aika kauan, siis vaihde päällä...

Yliaktiivinen jäsen Liittynyt: 17.10.2001 Viestejä: 6109 Paikkakunta: Hamina

Tukkoinen putsarihan ilmenisi mustana savuna perässä? Diisselihän tuottaa just sen verran tehoa mitä se saa löpöä eli jostain syystä kakku ei riitä. Fiksummat osaa varmaan neuvoa ruiskupumpun toiminnan tarkastamisesta.

Turbiinivika aiheuttaa vähän samanlaista vaivaa. Jos staattorin vapaakytkin hajoaa niin että se jumittaa staattorin niin käy juuri niin että auto hyytyy. Se vaikuttaa kylläkin enemmän ajonopeuksissa kuin liikkeelle lähdettäessä. Jos pumppu pimahtaa niin ei se kyllä kierrä vapaallakaan.

Vian täytyy olla ite koneessa tai apulaitteissa, ei laatikos tai turbiinissa...... Niin neuvoja odotellahan innolla edelleen!

Vakiokävijä Liittynyt: 19.08.2002 Viestejä: 678 Paikkakunta: Otalampi/Vihti

Chevyissä on aika usein siirtopumppuongelmia.Sammuilevat miten sattuu ja saa ihme kiihdytyshepuleita ja kaikki johtuu siirtopumpusta.Pumput vuotaa prässiliitoksesta.

[ Tätä viestiä muokkasi: mjo33400 2002-09-12 20:14 ]

Otin letkun siirtopumpun jälkeen käteen ja pistin letkun pään pulloon. Käynnistettäessä(kone ei käynnistä) naftaa tulee kahden sekunnin välein noin desi sykäyksinä! eli kuuluuko polttoainetta tulla tähän tyyliin? kaveri puhu, että olisko ohivuotomittauksesta jotain apua ja missä sen voi tehä?

joo...savua ei tosiaan paljoa tule. savuarvo kevään katsastuksessa oli 0,78. Voiko syöttöä muka itse säätää? oon ainakin kuullu, että se pitäs säädättää jossain muualla kuin kotona! no, joka tapauksessa, mistä sitä syöttöä voi säätää, vai onko se kenties mallista kiinni, että sitä ylipäätään voi säätää ollenkaan mistään ruuvista? Kannattaako ajoitusta lähteä säätämään ollenkaan, koska kone käy tasaisesti ja lähtee hyvin käyntiin kylmänä ja kuumana, ku vaan solenoidi tykkää pelata..heh! Kulutus kyllä on ihan normaali, että eikös kulutuksen pitäis pienentyä jos syöttö on pienemmällä?

Vakiokävijä Liittynyt: 27.09.2002 Viestejä: 864 Paikkakunta: Ylihärmä

tuli tos vaan mieleen et auto ei kesäkuumalla lähe kovin hyvin käymään jos ei hehkuta ollenkaan...vaikka kone olis seissy vaan viis minuuttia nii ei lähe ilman että polkasee vähän kaasua...kaverin auto lähtee monen tunnin seisomisenkin jälkeen heti käymään ilman hehkua viileemmälläkin ilmalla...eli mihin tällainen ilmiö viittaa? tietäjät kertokoon tietonsa!!

Vakiokävijä Liittynyt: 27.09.2002 Viestejä: 864 Paikkakunta: Ylihärmä

hehkut on iskus...tarkistin juur kun viriteltiin porukalla jälkihehku toimimaan..voiko kansipahvi vuotaa niin että se tekis moottorista tehottoman?

Sun kannattaa mitata puristuspaineet, pitäisi olla yli 25bar hyvällä akulla jos alle 20bar niin ei lähde helpolla käymään vaikka kuinka hehkuttais. suurin syy heikkoihin puristuksiin on jumittuneet männänrenkaat.

Aktiivijäsen Liittynyt: 10.12.2003 Viestejä: 3669 Paikkakunta: Ylästö

Toivottavasti näistä on apua, tee ihmeessä puristusmittaus!

Any cold 6.2L/6.5L GM diesel at ambient temperatures above 30° (-1° C) should start in less than 5 seconds of cranking, with 1-3 seconds being the norm for most GM diesel engines. The engine will then take another 5 seconds or so to settle down to a smooth fast idle after a cold start. A warm engine that has been recently run should start almost instantly with a smooth idle. An engine plugged in overnight should be at about 80-100° (26-38° C), but since the fuel pressure has had time to bleed down, it'll still take about 1-3 seconds of cranking to start and take a couple more seconds to settle down.

A cold DB2 equipped engine is normally started with about ¼-½ throttle and a warm recently run engine should start well with a throttle position just off idle. The computer on the DS4 equipped 94 and newer trucks makes the throttle application decisions for cold starting and does not require any input from the driver. Some diesel owners let the glow plugs go through 2 cycles or more before cranking a cold engine.

Fuel Filters

The very first item to be concerned about whenever a performance problem develops is the fuel filter(s). Filters are relatively inexpensive, and should be changed before you do anything else. Clogged fuel filters could contribute to hard starting by creating a fuel starvation problem during initial startup and before the fuel pumps have generated sufficient fuel pressure.

You can get a contaminated tank of fuel at any time. You shouldn't automatically rule out clogged fuel filters as the cause of your running or starting problems just because they were recently changed.

GM diesel trucks from 1984 to at least the early 90s incorporate a Stanadyne model 80 fuel filter assembly that uses a rectangular fuel filter cartridge. These filter assemblies can be sources of potential air or fuel leaks in a couple of ways:

The filter assembly base uses two plastic valves, one is used to drain water or fuel from the filter and the other to allow air to escape when installing a new filter. Ensure these valves are securely tightened after any service is performed. New valve seals are available from GM.
The filter base also incorporates a plastic water sensor probe that extends into the filter cartridge. This sensor probe is easily broken if the filter cartridge is rocked side-to-side when removing or replacing the filter. If the probe is cracked or broken, a poor sealing condition at the probe entry point will manifest itself as either a fuel or air leak.
The early model 80 filter base also incorporated a pressure switch that was used to monitor fuel pressure. When the pressure dropped below a certain pre-set level, a light on the dash illuminated indicating the filter needed to be changed. This pressure switch became a source of frequent air and fuel leaks, and was later dropped from production. GM even came out with a TSB instructing service technicians in how to eliminate this switch. The switch can be removed and the 3/16" hole in the filter housing can be tapped for a screw, eliminating this source of leakage.
Battery Voltage

Ensure your alternator is fully charging the batteries. The battery voltage at idle should be in excess of 14 vdc.

When batteries age, they lose a certain amount of their voltage capacity. They might have enough reserve cranking capacity to spin the engine normally, but the nominal voltage level of aging batteries can drop below an optimum level required to adequately light the glow plugs. Wattage is the product of voltage x amps.

To see if low battery voltage is contributing to hard starting, jump the driver's side battery with a known good battery. If you see a noticeable improvement in the way your truck starts, then you'll need to consider getting new batteries. Buy the highest capacity (1000 CA) maintenance free batteries that will fit into the battery mounts.

Glow plugs and controller circuit

A GM diesel will become somewhat more difficult to start cold with just one or two inoperative glow plugs.

See the following chapters for an in-depth examination of the GM glow plug system.

Fuel Lift Pump

The fuel lift pump (the one on the lower right side of the engine block on the 6.2s) could cause a hard starting situation. The 6.5 electric lift pump is located under the cab against the frame. If the pump is not developing adequate fuel pressure, the injection pump could be starved for fuel at startup. If the pump's check valve doesn't prevent fuel from being drawn from the injection pump while at rest because of the normal vacuum in the fuel tank, the injection pump could be starved for fuel during the first moments of startup. This problem is usually worse the longer it sits. A serious hard starting situation can develop when a leaky injector is combined with a bad check valve in the lift pump. Air will migrate up the injector line(s) when the engine is off. If air makes it's way to the injection pump, you'll have an air-lock. I recommend changing the fuel lift pump if your starting problem could be related to "fuel drain-back".

Since 1991, GM recommends using their new 6.2L fuel lift pump (P/N 25116503) which uses a "ventless" check valve to prevent fuel drain back. Any aftermarket brand should be of similar construction.

Adding an electric fuel pump to older 6.2L trucks originally equipped with a mechanical lift pump may help cold starting. An electric fuel pump would pressurize the fuel system before the starter is engaged.

All 6.5 diesels came factory equipped with an electric fuel pump. The electric fuel lift pump used in the newer fuel systems is powered by a relay while you're cranking the engine and powered through an oil pressure switch when the engine is running. Opening the fuel filter drain valve while either cranking the engine or with the engine idling will tell you if the electric fuel lift pump is functioning. Always eliminate the relay and oil pressure switch as the cause of no lift pump fuel pressure before replacing the electric fuel lift pump.

At a normal cranking speed, the minimum allowable pressure measured at the outlet side of the lift pump is 2 psi, and the flow volume should be at least 1/2 pint in 15 seconds. Having both the correct fuel pressure and pumping volume is equally important.

Fuel Line Air Leak

Any air that gets into the fuel system will dramatically increase the difficulty of cold starting. The most likely place for air to enter the fuel system is the fuel line from the primary lift fuel pump back to the tank because the fuel line on that side of the fuel pump is always under vacuum. From the primary fuel pump through the injection pump and to the injectors, the fuel is under pressure and you'll probably see evidence of a leak in the form of leaking fuel. Check all of the fuel line hoses, fittings, clamps and tank switcher from the primary fuel pump back to the tank for tightness and integrity. Replace any components that are questionable. At the same time, make sure the metal fuel line carrying fuel from the tank to the fuel pump isn't rubbing on anything that could wear a hole in it. Pressurizing the fuel tank with an air hose at no more than 10-15 psi could show a fuel line air leak in this area.

Air in the injection system will either make it's way through the injector nozzles or more likely be re-cycled back to the tank in the fuel return line (assuming your engine will run). The neoprene fuel return lines from the injection pump and the injectors can be temporarily replaced with suitably sized clear tubing. This will allow you to check for air bubbles that made their way through the injection system. After installing the clear tubing and running the engine for a couple of minutes, there shouldn't be any air in the system. If you see any bubbles, you need to track down the source of the air leak. As mentioned earlier, the source of most air leaks in a running engine usually occurs upstream from the injection pump. A blockage in the tank (water, algae or debris), plugged fuel filters or a defective tank switcher can cause a significantly higher than normal level of suction to be felt on these fuel supply lines which can cause a line or fitting to leak air where it normally wouldn't otherwise. A pressure and volume test done on the lift pump would highlight any problem in this area. Low volume and/or pressure would indicate a bad lift pump or a blocked fuel line supply.

If you only see air bubbles in the fuel return lines for the injectors after a cold start or after the engine has been off for a while, then one or more injectors are bleeding air back into the injection system. The injector nozzles are not adequately sealing when the engine is off. Installing a new set of injectors is the usual remedy. More information concerning injectors can be found elsewhere in this guide.

Cold Advance/Fast Idle Functions

At engine temperatures below 125° F a "Cold Advance" switch supplies 12 volt power to the HPCA (Housing Pressure Cold Advance) solenoid in the injection pump housing and to the "Fast Idle" solenoid that acts on the throttle arm of the injection pump. An energized cold advance solenoid will advance the injection pump timing approximately 3-5°. This additional timing advance and fast idle aids in both cold starting and warm-up.

Under normal circumstances, owners will notice more diesel engine "rattle" and a faster idle during warm-up. As soon as the engine temperature exceeds 125°, the "rattle" will diminish and the fast idle will be disengaged. This indicates the "cold advance" switch has removed power from the two previously mentioned solenoids. If you're not experiencing an increased "rattle" or a faster idle during warm-up, you should determine if the fault is with the "cold advance" switch or with the solenoids in the injection pump housing and the "fast idle" assembly. The "cold advance" switch is located in the lower rear corner of the passenger side head. The switch has an electrical connector with 2 wires running to it. This switch should pass 12 volt battery power through to the injection pump when the engine temperature is below 125° F. A voltmeter can be used to verify correct switch functioning. By disconnecting and re-connecting the electrical connector on the injection pump that powers the "cold advance" solenoid, you should be able to verify whether the solenoid is correctly activating the "cold advance" mechanism within the pump. The injection pump timing should advance and cause a more pronounced diesel engine "rattle", and the engine RPM should increase when these solenoids are energized.

Injection Pump and Injectors

These components represent some of the more expensive components that could contribute to hard starting and I recommend you experiment with some of the other possible contributors listed before replacing the injection pump or injectors. If your pump and injectors have in excess of 100,000 miles on them, you might consider changing them. Low time pumps and injectors should be tested at a rebuilding facility before replacement if you think they are causing your hard starting problem.

Over time, the injection pump timing will slowly retard due to wear of the timing components (timing chain, sprockets and gears). The timing should be checked and re-set every 50-100,000 miles. Injectors will wear over time as well. Many times, a mildly hard starting GM diesel will result from several relatively minor changes in the injection system. In this situation, I would have the injection pump re-timed and then have the injectors "POP" tested.

A new HPCA (Housing Pressure Cold Advance) regulator valve assembly (GM P/N-10149645) replaces the older style ball check valve in the fuel return section of the injection pump and was introduced in October of 1991 for installation in all earlier 6.2L DB2xxx pumps. This modification will help to reduce the fuel drain-back problem that leads to fuel starvation at a cold start. GM further recommends that the new mechanical lift pump (P/N 25116503) be installed (except those models with electric lift pumps) at the same time as part of a comprehensive fuel "drain-back" mitigation program.

A leaky injector could allow air to bleed back into the injection system when the engine is off, especially if the check-valves in the lift and injection pump aren't doing their job. This air bleedback will definitely cause your truck to start harder and the degree of difficulty usually increases the longer the truck sits between starts (more time=more air).

Elevation

Cold starts are more difficult at elevations higher than about 5,000 feet due to the lower concentration of oxygen in the atmosphere. A combustion enhancing fuel additive usually helps in these situations.

Fuel Quality

Contaminated or poor quality fuel is known to be a hard starting contributor. Diesel fuel available through high volume dealers is usually more fresh and is less likely to be contaminated. The smaller fuel dealers that don't see as much truck traffic could pose a problem with poor quality fuel. Most experienced diesel owners buy their fuel from high traffic fuel dealers as a precaution against having diesel injection system problems.

If you've been experiencing problems with contaminated fuel or are experiencing hard starting, a switch in diesel fuel stations may help.

Engine compression

Part of a hard starting troubleshooting plan should eventually include a compression check. New engines will have close to 400 psi of compression at cranking speed and a high-time engine could be as low as 275 psi. If your compression pressure is close to 275, then it's probably time to think about rebuilding the engine.

Starting Fluid

GM explicitly warns against using starting fluid in the 6.2L/6.5L. Starting fluid (ether) in combination with a glow plug system can create explosions powerful enough to blow head gaskets, damage pistons, or even stretch head bolts. Consequently, most diesel mechanics agree that WD-40 spray is the preferred alternative to an ether based starting fluid.

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