Diesel Compression & Pressure Test Adapters
Compression test adapters, fuel pressure and restriction gauges, and quick-connect diagnostic test fittings — the hardware that lets you put a real number on a diesel instead of guessing.
Diagnosing a diesel means reading pressures: cylinder compression, fuel supply and restriction, and high-pressure oil on the platforms that use it. Each of those readings needs an adapter that threads into a specific port — an injector bore, a glow plug hole, a fuel gallery test point — and seals properly at pressure. Use the wrong adapter and you either cannot connect or you get a reading you cannot trust.
This page collects Ferrum's test adapters and gauges by job: compression adapters for common engine families (CAT 3126/3126B/3126E, DT466E and Maxxforce DT, 3208), fuel pressure and restriction gauge sets, quick-connect test fittings compatible with Compucheck-style test points, and the high-pressure oil / IPR air test tooling for 6.0L and 7.3L Powerstroke.
A note on naming: "Compucheck" is a registered trademark of its owner. The fittings listed here are compatible alternatives designed to work with that style of test point — they are not Compucheck-brand products, and Ferrum is not affiliated with the trademark holder.
Shop Diesel Compression & Pressure Test Adapters
How to Choose
Start from the port, not the gauge
The gauge is usually the easy part — the adapter that threads into your engine is what determines whether the test is possible. Identify the engine family and the test port (injector bore, glow plug, fuel gallery test point) first, then pick the adapter that matches, then confirm the gauge range covers the pressure you expect.
Compression testing needs the right seat
A diesel compression adapter has to seal against combustion pressure, which is an order of magnitude above a gasoline engine. Adapters are cut for specific bores — a 3126B adapter is not a DT466E adapter. Using an adapter that almost fits produces a low reading that sends you chasing a problem that is not there.
Fuel restriction is a different test from fuel pressure
Supply pressure tells you what the pump is delivering; restriction tells you what the filter and lines are taking away. A restriction gauge reads vacuum on the suction side. Diagnosing a hard-start or power-complaint properly usually means measuring both, which is why they are commonly sold as a combined set.
Quick-connect test points save the repeat job
If you service the same fleet repeatedly, permanently-installed test fittings let a tech take a reading in seconds without cracking a line — no fuel spill, no air introduced into the system. That is the reason the Compucheck-style fitting exists and why fleets standardize on them.
Frequently Asked Questions
What is a Compucheck fitting?
It is a quick-connect diagnostic test point that lets a technician attach a gauge to a pressurized system without opening a line. "Compucheck" is a trademarked brand of that style of fitting; compatible alternative fittings from other manufacturers perform the same function. Ferrum stocks compatible alternatives and is not affiliated with the trademark holder.
What adapter do I need for a diesel compression test?
One cut for your engine's test port. Most heavy-duty diesels are tested through the injector bore, so the adapter must match that bore's thread and seat — for example, CAT 3126/3126B and International DT466E use different adapters. Check the OEM cross-reference listed on each product against your engine.
Can I use a gasoline compression tester on a diesel?
No. Diesel compression runs far higher than a gasoline engine, so the gauge range and the adapter sealing are both inadequate, and the readings are meaningless at best. Diesel testing requires a diesel-rated gauge and an engine-specific adapter.
What is the difference between fuel pressure and fuel restriction testing?
Fuel pressure measures what the supply system delivers on the pressure side. Fuel restriction measures the vacuum created by filters and lines on the suction side. A restricted filter can starve an engine while supply pressure still looks acceptable at idle, so both readings are usually needed for a complete diagnosis.
Shop by Engine
Looking for tooling for a specific platform? Browse the engine-specific ranges:
Need Help Identifying the Right Tool?
Our team works with these engines every day. Contact us with your engine model and OEM tool number and we'll confirm the fit.